northern territory department of …...most other definitions may be found in jackson (1997). mga...
TRANSCRIPT
NORTHERN TERRITORY DEPARTMENT OF BUSINESS, INDUSTRY AND RESOURCE DEVELOPMENTNORTHERN TERRITORY GEOLOGICAL SURVEY
Government Printer of the Northern Territory Darwin, May 2002
AYERS ROCK, Northern Territory (Second Edition)
Sheet SG 52-8
1:250 000 GEOLOGICAL MAP SERIES EXPLANATORY NOTES
DN YOUNG, N DUNCAN, A CAMACHO, PA FERENCZI and TLA MADIGAN
SG 53-1HENBURY
SG 52-3BLOODS RANGE
SG 53-9ALBERGA
SG 52-7PETERMANN RANGES
SG 53-5KULGERA
SG 52-11MANN
27˚00'27˚00'129˚00'
129˚00'24˚00' 24˚00'
133˚30'
133˚30'
SG 52-4LAKE AMADEUS
SG 52-12WOODROFFE
SOUTH AUSTRALIA
NORTHERN TERRITORY
MT OLGA5047
CURTIN5247
ALLANAH5046
BRITTENJONES5146
AYERSROCK5147
AYERS ROCKSG 52-8
MULGAPARK5246
ii
NORTHERN TERRITORY DEPARTMENT OF BUSINESS, INDUSTRY AND RESOURCE DEVELOPMENT
MINISTER: Hon Paul Henderson, MLA
CHIEF EXECUTIVE OFFICER: Peter Blake
NORTHERN TERRITORY GEOLOGICAL SURVEYDIRECTOR: Dr R Dennis Gee
BIBLIOGRAPHIC REFERENCE: Young DN, Duncan N, Camacho A, Ferenczi PA and Madigan TLA, 2002. Ayers Rock, Northern Territory (Second Edition). 1:250 000 geological map series explanatory notes, SG 52-8. Northern Territory Geological Survey, Darwin.
(1:250 000 geological map series, ISSN 0814-7485)Bibliography
ISBN 0-7245-7009-8 (Hard copy) ISBN 978-0-7245-7140-6 (CD version) 559.429
KEY WORDS: Geological mapping, Structural geology, Metamorphism, Geochronology, Geochemistry, Economic geology, Sedimentary geology, Northern Territory, Mesoproterozoic, Neoproterozoic, Palaeozoic, Mesozoic, Cenozoic, Ayers Rock, Uluru, Mount Olga, Kata Tjuta, Musgrave Block, Fregon subdomain, Mulga Park subdomain, Amadeus Basin, Musgravian Event, Petermann Orogeny, Alice Springs Orogeny, Granite, Gneiss, Charnockite, Dolerite, Pseudotachylite.
For further information contact:Reference GeologistNorthern Territory Geological SurveyGPO Box 3000Darwin NT 0801Phone: +61 8 8999 5281Web site: http://www.minerals.nt.gov.au/ntgs
© Northern Territory Government 2002
Printed and published for the Northern Territory Geological Surveyby the Government Printer of the Northern Territory
DisclaimerThis information is provided on the understanding that the user agrees to release and indemnify the Northern Territory, the Commonwealth of Australia, companies who supplied and acquired the data, and their employees, agents and contractors, in respect of all liability for actions, claims, costs, expenses, loss, damage or injury, which may be suffered by them, or any other persons, arising from the users use of the data, or as a consequence of any unlawful or negligent act or omission of the user.
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ABSTRACT
AYERS ROCK1 is located in the arid southwest of the Northern Territory. It features a largely granitic Mesoproterozoic basement complex in the south (northern part of the Musgrave Block plus some interthrusted and metamorphosed lower units of the Amadeus Basin) and Neoproterozoic to Palaeozoic sedimentary rocks in the north (largely unmetamorphosed Amadeus Basin rocks). The Musgrave Block in AYERS ROCK is composed of two subdomains of granite and granitic gneiss; these are the amphibolite facies Mulga Park subdomain and the granulite facies Fregon subdomain. Cenozoic sediments form a sur cial cover over the majority of the sheet.
The oldest rock unit recognised (Allanah Gneiss) is granitic and in places migmatitic due to amphibolite facies metamor-phism. It has yielded U-Pb zircon dates of 1550 Ma, interpreted to be the igneous age, and 1200 Ma, interpreted to be the age of Musgravian Event metamorphism. Large outcrops of Allanah Gneiss are rare; it generally forms roof pendants and xenoliths within younger granites in the Mulga Park subdomain. The Fregon subdomain is thrust over the Mulga Park subdomain and consists of gneiss, which is mainly of granitic and lesser metasedimentary and intermediate compositions. Granulite facies gneiss may be a deeper crustal equivalent of the Allanah Gneiss. A succession of amphibolite facies schist, quartzite and ma c amphibolite (Opparinna Metamorphics) occurs in the Kelly Hills (Mulga Park subdomain) in southeastern AYERS ROCK. This succession may be as old as 1600 Ma and is intruded by granite that is probably 1150 Ma in age. The schist contains Mn-rich minerals such as viridine (Mn-andalusite).
An extensive series of granite intrusions (Kulpitjata Granite Complex) were emplaced at 1200-1150 Ma, following the Musgravian Event. The Kulpitjata Granite Complex is dominated by biotite granites of variable grain size but with similar mineralogy and geochemistry. Additional granitic and charnockitic magmatism occurred at 1060 Ma, as is recognised from rocks in a small area in southeastern AYERS ROCK (Michel Nob Granite and Nulchara Charnockite) and from rhyolitic clasts in the Mount Currie Conglomerate.
Numerous dolerite dykes cut granite and gneiss in southwestern AYERS ROCK and these belong mainly to the 1080 Ma Alcurra Dyke Swarm (Edgoose et al 1993). Some ma c dykes are considered to be equivalent to the Mummawarrawarra Basalt of the 1080 Ma Tollu Group (Sheraton and Sun 1997). It is possible that equivalents to the 820 Ma Amata Dyke Swarm (Zhao and McCulloch 1993) may also be present.
Neoproterozoic Amadeus Basin sediments were deposited from about 830 Ma and comprise the basal Dean Quartzite and overlying Pinyinna beds, Inindia beds and Winnall beds. In parts of southern AYERS ROCK, the lower two units are deformed and metamorphosed with granite and gneiss of the Musgrave Block. The Inindia and Winnall beds are preserved as gently folded strike ridges in northern AYERS ROCK, along with Cambrian and Ordovician sedimentary rocks and small outcrops of the Bitter Springs Formation (equivalent to the Pinyinna beds).
During the north-vergent 560-530 Ma Petermann Orogeny, a weak to pervasive mylonitic foliation was developed in all granitic and gneissic rocks of the crystalline basement. The Dean Quartzite and Pinyinna beds were interthrusted and meta-morphosed with Musgrave Block granitic rocks. In places, kyanite formed in the Dean Quartzite and secondary minerals, such as muscovite and garnet, formed in granitic rocks. Granulite facies rocks were thrust over amphibolite facies rocks along the south-dipping Woodroffe Thrust. This regional-scale structure is a zone of mylonite and ultramylonite and has extensive development of pseudotachylyte.
In the southern Amadeus Basin, the Petermann Orogeny interrupted latest Neoproterozoic to Cambrian sedimentation. Deposition of the syn-orogenic Mount Currie Conglomerate and Mutitjulu Arkose took place in high-energy uvial settings adjacent to the emerging Petermann Ranges. Sedimentation within the basin was terminated by the Alice Springs Orogeny at approximately 350 Ma.
1 Names of 1:250 000 and 1:100 000 map areas are given in large and small capitals respectively; eg AYERS ROCK, MULGA PARK.
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CONTENTS
Abstract .................................................................................................................................................................................... iiiIntroduction ...............................................................................................................................................................................1
Terminology ......................................................................................................................................................................... 1Location and access ............................................................................................................................................................. 1Climate ................................................................................................................................................................................. 2Vegetation ............................................................................................................................................................................ 2Physiography ........................................................................................................................................................................ 3Early exploration .................................................................................................................................................................. 3Geological and geophysical investigations .......................................................................................................................... 3
Regional geological setting ..................................................................................................................................................... 5Musgrave Block ......................................................................................................................................................................... 8Fregon subdomain ........................................................................................................................................................................ 8
Felsic granulite gneiss (LPfg) ................................................................................................................................................. 8Nulchara Charnockite (LPgn)................................................................................................................................................. 8Mylonite and pseudotachylyte (LPm) .................................................................................................................................... 8
Mulga Park subdomain ................................................................................................................................................................ 8Older units ................................................................................................................................................................................ 8
Allanah Gneiss (LPnga) ......................................................................................................................................................... 8Basement quartzite (LPq) ....................................................................................................................................................... 9Opparinna Metamorphics (LPop) ........................................................................................................................................... 9Undivided granite and gneiss (LPgu) ................................................................................................................................... 10
Kulpitjata Granite Complex ................................................................................................................................................... 10Yununba Granite (LPgky) .................................................................................................................................................... 10Katiti Granite (LPgkk) .......................................................................................................................................................... 10Undivided Kulpitjata Granite Complex (LPgk) ................................................................................................................... 11
Younger igneous rocks ........................................................................................................................................................... 13Michell Nob Granite (LPgm) ............................................................................................................................................... 13Dolerite dykes and gabbro (LPdl) ........................................................................................................................................ 13Amphibolite (LPam) ............................................................................................................................................................. 13
Amadeus Basin ........................................................................................................................................................................14Dean Quartzite (LPde) .......................................................................................................................................................... 14Pinyinna beds (LPpi) ............................................................................................................................................................ 14Bitter Springs Formation (LPbi) ........................................................................................................................................... 15Inindia beds (LPin) ............................................................................................................................................................... 16Winnall beds (LPwi) ............................................................................................................................................................. 16Mount Currie Conglomerate (–Cc) ...................................................................................................................................... 17Mutitjulu Arkose (–C m) ..................................................................................................................................................... 19Stairway Sandstone (Os) .................................................................................................................................................... 20Stokes Siltstone (Ot) .......................................................................................................................................................... 21Carmichael Sandstone (Oc) ............................................................................................................................................... 21Horseshoe Bend Shale (Dh) ............................................................................................................................................... 22
Mesozoic and Cenozoic sediments .........................................................................................................................................22 Mesozoic Sediments .................................................................................................................................................................. 22Cenozoic Sediments ................................................................................................................................................................... 22
Non-exposed Cenozoic sediments ..................................................................................................................................... 22Sandstone (Czs) ................................................................................................................................................................. 22Talus and scree (Czt) .......................................................................................................................................................... 22Skeletal residual soil (Cz) .................................................................................................................................................. 22Ferricrete (Czf) ................................................................................................................................................................... 22
Quaternary Sediments ............................................................................................................................................................... 23Calcrete (Qc) ...................................................................................................................................................................... 23Talus (Qt) ........................................................................................................................................................................... 24Playa sediments (Qp) ......................................................................................................................................................... 24Gypsiferous deposits (Qpg) ............................................................................................................................................... 25Colluvium (Qr) ................................................................................................................................................................... 25Aeolian sand (Qs) .............................................................................................................................................................. 25Alluvium (Qa) .................................................................................................................................................................... 25
Structure and metamorphism ............................................................................................................................................... 25Musgravian Event .............................................................................................................................................................. 26
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Petermann Orogeny ........................................................................................................................................................... 26Alice Springs Orogeny ....................................................................................................................................................... 26
Geochemistry ........................................................................................................................................................................... 26Granitic rocks ............................................................................................................................................................................. 26
1550 Ma granitic gneiss ..................................................................................................................................................... 261150 Ma granitic rocks....................................................................................................................................................... 261050 Ma granitic rocks ...................................................................................................................................................... 26
Ma c rocks ................................................................................................................................................................................. 28Quartzite ..................................................................................................................................................................................... 28Geochronology ......................................................................................................................................................................... 28U-Pb zircon geochronology ....................................................................................................................................................... 28
1600 Ma zircons in Opparinna Metamorphics ................................................................................................................... 281550 Ma granitic gneiss ..................................................................................................................................................... 281150 Ma granites ................................................................................................................................................................ 291050 Ma magmatism .......................................................................................................................................................... 29
Sm-Nd isotopic data ................................................................................................................................................................... 29K-Ar and Rb-Sr isotopic data .................................................................................................................................................... 29Geological history .................................................................................................................................................................... 29Economic geology .................................................................................................................................................................... 30
Hydrocarbons ..................................................................................................................................................................... 30Phosphate ........................................................................................................................................................................... 30Zeolites ............................................................................................................................................................................... 30Metalliferous potential ....................................................................................................................................................... 30Groundwater ...................................................................................................................................................................... 30
Acknowledgements ................................................................................................................................................................. 30References ............................................................................................................................................................................... 31
APPENDICES
1 De nitions of new stratigraphic names .............................................................................................................................. 362a Geochemical analyses of gneiss, granite, charnockite and rhyolite clasts .......................................................................... 402b Geochemical analyses of Kulpitjata Granite Complex ....................................................................................................... 412c Analyses of ma c dykes ..................................................................................................................................................... 442d Rare earth element analyses of quartzite ............................................................................................................................ 452e Samarium-Neodymium and Rubidium-Strontium analyses of selected samples ............................................................... 46
TABLES
1 Rock units of the Musgrave Block in AYERS ROCK .......................................................................................................... 62 Stratigraphy of the Amadeus Basin in AYERS ROCK ......................................................................................................... 73 Summary of geochronological data for AYERS ROCK ..................................................................................................... 28
FIGURES
1 Location of AYERS ROCK .................................................................................................................................................. 12 Mean temperature and rainfall data for Uluru ...................................................................................................................... 23 Uluru ..................................................................................................................................................................................... 44 Kata Tjuta ............................................................................................................................................................................. 45 Kelly Hills, viewed from the east ......................................................................................................................................... 46 Pseudotachylite veins cutting granulite gneiss ..................................................................................................................... 97 Gneissic layering in Allanah Granitic Gneiss ..................................................................................................................... 108 Medium megacrystic granite in Kulpitjata Granitic Complex............................................................................................ 119 Medium granite in Kulpitjata Granitic Complex ................................................................................................................ 1210 Coarse granite in Kulpitjata Granitic Complex .................................................................................................................. 1211 Mylonitised granite in Kulpitjata Granitic Complex .......................................................................................................... 1312 Tight folds in Dean Quartzite ............................................................................................................................................. 1413 Sandstone lenses in lower member of Mount Currie Conglomerate .................................................................................. 1714 Thick exposure of upper member of Mount Currie Conglomerate .................................................................................... 1815 Close up of polymictic conglomerate from upper member of Mount Currie Conglomerate ............................................. 1816 Near-vertical beds of Mutitjulu Arkose at Uluru ................................................................................................................ 1917 Trough crossbeds in Mutitjulu Arkose ................................................................................................................................ 20
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18 Photomicrograph of Mutitjulu Arkose, showing coarse, angular feldspar-rich grains ....................................................... 2119 Isopach map showing thickness of Cenozoic deposits ....................................................................................................... 2320 Regional extent of playa lake system and major drainage channels ................................................................................... 2421 Selected Harker variation diagrams for granitic rocks ....................................................................................................... 27
� �
IntroductIon
These Explanatory Notes were compiled from the work of various NTGS geologists and are based on field mapping and geophysical interpretation. Airborne geophysical surveys were flown in the south and west in 1986 and 1988, and completed in the northeast in 2000. Mapping commenced on pastoral areas, which comprise the eastern third of the area, during 1989-90. The remaining four 1:100 000 map sheets, which include Aboriginal Land Trust areas, were mapped mainly during 1992-95 and additional field checking was undertaken in 1996-97. Mapping utilised 1:25 000 colour and 1:50 000 colour and black and white aerial photographs. The original work is featured in NTGS technical reports (Camacho 1991, Young 1992) and in internal reports written during 1995-98 that are available in digital form from NTGS Alice Springs. First Edition mapping of AYERS ROCK was conducted by the Bureau of Mineral Resources2 in the early 1960s (Forman 1965).
The rock descriptions in these explanatory notes are considered to be an accurate portrayal of the geology of AYERS ROCK, within the limits of available access. They are accompanied by high quality new geochronological and geochemical data. For a full interpretation of the Musgrave Block in the Northern Territory, including its structure and
metamorphism, refer to reports on nearby areas (Edgoose et al 1993, Camacho and Fanning 1995, Camacho et al 1995, Scrimgeour et al 1999) and to a forthcoming NTGS summary (Edgoose et al 2002).
Terminology
Igneous rock nomenclature follows Le Maitre (1989). Sedimentary rock terminology follows Pettijohn et al (1973). Most other definitions may be found in Jackson (1997). MGA grid references are based on the GDA94 datum, and are quoted in the text as universal grid references (UGR: see map face for explanation). Chronometric ages are given in Ma (millions of years before present). Where a specific age determination is used, the error range and author attribution is given. Where a general chronometric age or age range is used, the figure in Ma is rounded, no error is given and an approximate value is implied.
Location and access
AYERS ROCK lies between 25º00’S and 26º00’S, and 130º30’E and 132º00’E, to the north of the Northern Territory-South Australia border (Figure 1), and is centred 330 km to the southwest of Alice Springs. The four western 1:100 000
Railway
Vehicle track
Town, settlement Homestead
24 00’133 30’O
O
27 00’133 30’O
O
26 00’
25 00’O
O
Imanpa
Erldunda
Kulgera
Lyndavale
De Rose Hill
VictoryDowns
PalmerValley
HIG
HW
AY
ST
UA
RT
James Ranges
HIGHWAY
River
FINKE
RIVER
129 00’24 00’O
O
27 00’129 00’
O
O
25 00’
26 00’O
O
130 30’ 132 00’O O
130 30’ 132 00’OO
Mt EbenezerCurtinSprings
Pukatja
AngusDowns
Ranges
Ker rotRanges
LASSETER
Palmer
George Gill
(Agnes Creek)
MtCavenagh
Amata
Yulara
NORTHERN TERRITORY
SOUTH AUSTRALIA
Pipalyatjara(Mt Davies)
AVEGRMUS RANGES
Finke GorgeNational Park
ABORIGINAL
LAND
TRUST
NORTH-WEST ABORIGINAL RESERVE
25 50 75 100km0
HenburyHenburyMeteoriteCraters
Mulga Park
Fregon
Sealed highway/road Minor unsealed road
WE
ST
ER
N A
US
TR
ALI
A
NO
RT
HE
RN
TE
RR
ITO
RY
Watarrka National Park
AMADEUS
LAKE
Kaltukatjara(Docker River)
NEALELAKE
Areyonga
UluruUluru National Park
Figure 1. Location of AYERS ROCK
2 BMR, now Geoscience Australia.
2
map sheets are located mainly within Aboriginal Land Trust areas. These Land Trust areas enclose Uluru - Kata Tjuta National Park, for which freehold title was handed back to Traditional Custodians in 1985. The park was then leased back on a 99 year term to the Federal Government. An area abutting the Park and enclosing Yulara resort and airport is freehold land held by the Ayers Rock Resort Company. The two eastern 1:100 000 map sheets largely coincide with the Curtin Springs and Mulga Park pastoral properties.
The sealed Lasseter Highway links Yulara to Erldunda on the Stuart Highway, which is 245 km to the east of Yulara. To the west of Yulara, the sealed road continues for 48 km to Kata Tjuta. Beyond this point, a formed-gravel road continues westwards to the WA border as the Docker River (Kaltukatjara) road. The old formed-gravel Petermann road, which is the original link between Curtin Springs and Uluru, still exists in relatively good condition, to the south of and parallel to the Lasseter Highway. Two other formed-gravel roads provide access to the Amata community in South Australia. One is Amata road, which is oriented north-south next to Britten Jones Creek. This road connects with the old Petermann road to the east of Uluru. The other road connects the Lasseter Highway east of Curtin Springs to Amata via Mulga Park. Within the two pastoral properties, a network of station tracks and some cleared seismic lines on Curtin Springs provide vehicle access. Elsewhere, there are a number of either graded or unformed tracks. In many places, thick mulga scrub or sand dunes limit access to both Aboriginal and Pastoral land.
Climate
AYERS ROCK has a semi-arid climate with low humidity and is subjected to long hot summers and mild winters. A summary of the temperature and rainfall data for Yulara is shown in Figure 2. January is the hottest month with an average daily maximum temperature of 37.5ºC and a minimum of 21ºC. July is the coldest month with an average daily maximum of 20ºC and a minimum of 3.5ºC. The average annual rainfall is 300-350 mm, most of which falls in summer. The rainfall is highly variable and recorded annual totals vary from 84-936 mm. There is an average of 47 rain days per year. Rainfall either in ltrates the ground or is lost by evaporation; it rarely forms a surface ow. The average potential evaporation is in the order of 10 times the average rainfall. Snowfalls were recorded at Uluru for the rst time in the modern era on July 11 1997.
Vegetation
The vegetation of AYERS ROCK mirrors, to a degree, the physiography of the area. The following summary is based upon Thompson and Kube (1990) and Urban (1990). Open plain woodlands and scrublands support a ora dominated by various Acacia species. Of these, the common mulga (Acacia aneura) is abundant, together with ironwood (Acacia estrophiolata) and witchetty bush (Acacia kempeana). A variety of Eucalyptus species occurs within the plains environment. Blue mallee (Eucalyptus gamophylla) is dominant and can be found concentrated in single species groves. Sharp-capped mallee (Eucalyptus oxymitra) is common, but has a scattered distribution. In sandy areas,
desert oak (Allocasuarina decaisneana) forms large groves or may be scattered. Desert grevillea (Grevillea juncifolia) and honey grevillea (Grevillea eriostachya) are also found in sandy areas, as are rare isolated groups of desert grass trees (Xanthorrhoea thorntonii) and rare isolated desert kurrajong (Brachychiton gregorii). Rare quandong (Santalum acuminatum) are found dotted over the plains or concentrated near drainage lines in the southeast. A variety of emu bush (Eremophila sp) and Cassia species, including desert cassia (Cassia nemophila) and grey cassia (Cassia desolata) are found on plains and to a lesser degree in hills.
Adjacent to hills and in areas of runoff, bloodwood (Eucalyptus centralis) is present, and fork-leafed corkwood (Hakea eyreana) and long-leafed corkwood (Hakea suberea) may also be found. Along the generally dry watercourses, river red gum (Eucalyptus camaldulensis) is common, and to the southeast amongst ranges and hills, the inland tea-tree (Melaleuca glomerata) is locally numerous. Low spindly Acacia species are the most abundant ora on hills and ranges, and the holly grevillea (Grevillea wickhamii) is locally common. Stands of native g (Ficus platypoda) grow amongst hills
Figure 2. Mean temperature and rainfall data for Uluru (data from Bureau of Meteorology)
DegreesCelsius
40
30
35
25
20
15
10
5
0Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Millimetres
100
90
80
70
60
50
40
30
20
10
0Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Mean maximum temperature Mean minimum temperature
Uluru average temperatures
Data used: 1968-1983
Uluru average rainfallData used: 1964-1983
48 46
52
2522 21
913
19
24
35
19
21.1 20.5
17.3
12.6
7.9
5.13.4
5.5
9.1
13.5
17.219.8
36.834.1
31.5
26.4
22.620.320.2
23.4
28.8
33.435.8
37.5
3
in places with suf cient water. Rare Eucalyptus species are also found.
Varieties of native grasses inhabit plains, sand dunes and water drainage lines. Of these native grasses, probably the best known is spinfex and in particular hard spinifex (Triodia basedowii). Several of the “softer” grasses are restricted to the immediate vicinity of signi cant runoff areas and are classi ed as rare and endangered species. These are only known from Uluru, Kata Tjuta and Mulya Iti. Elsewhere in the plains and sand dunes, are found species of daisy, Hibiscus parakeelya, pussytail, saltbush and solanum (including native tomato).
Physiography
AYERS ROCK is dominated by sand plains and dunes, and has scattered ranges and hills. In the west, both Uluru (Ayers Rock) and Kata Tjuta (Mount Olga) rise abruptly from sand plains (Figures 3, 4), as does Mount Conner (Atila) in the east. Ranges and low hills (eg Kelly Hills, Figure 5) dominate in the south near the border with South Australia. Low hills and strike ridges also occur in the northeast in CURTIN. There is a regional gradient of decreasing height from the southern ranges northwards to Lake Amadeus.
Forman (1965) described the physiography of AYERS ROCK, and recognised three types of ranges and hills:
• Ranges and hills of the south. These form a watershed, from which creeks generally drain northwards. They are a southeastern extension of the Olia Chain on PETERMANN RANGES, are dominated by granite and gneiss and commonly have a quartzite capping. The higher peaks rise 200-300 m above the surrounding plains and have elevations of up to 1086 m.
• Ranges and hills of the east. Mount Conner is a large mesa that has an elevation of 859 m. It consists of at lying sandstone (Winnall beds) in the core of a basinal structure and is surrounded by concentric ridges of sandstone (Inindia beds) that dip more steeply in toward Mount Conner.
• Ranges, hills and inselbergs of the centre and northwest. With the exception of Uluru, which is composed of Mutitjulu Arkose, these features are composed of Mount Currie Conglomerate. Uluru (863 m) is a solitary inselberg, whereas Kata Tjuta (1066 m) is part of a group. Both are distinctive and rise 300 m and 400 m, respectively, from the surrounding sand plains and dune elds. Mount Currie (664 m) in the northwest is similar in form to Kata Tjuta.
Low ridges and hills also occur in northeastern AYERS ROCK. Sand dunes are particularly common in central AYERS ROCK but occur throughout. They range in height from 6 m in the west to 12 m in the east. Salt lakes and associated calcrete and gypsum deposits occur mainly in the north as part of the Lake Amadeus chain of lakes.
Streams in the area are intermittent and only ow for a short period after signi cant rain. Britten Jones Creek drains northwards towards Lake Amadeus and is the largest drainage system. Only a few permanent-water rock holes of any consequence exist. Smaller rock holes provide only
a limited water supply after rain. Due to the lack of surface water, a large number of boreholes have been sunk for the pastoral industry, Yulara township, Mutitjulu community and Aboriginal outstations.
Early exploration
John Stuart, in 1865, was the rst non-Aboriginal man to traverse Australia from south to north via a route to the east of AYERS ROCK. In 1872, Ernest Giles traversing from the north, became the rst non-Aboriginal man to see Kata Tjuta when he encountered the northern edge of Lake Amadeus, which he was unable to cross. A year later, Henry Gosse visited and proposed the names Ayers Rock (for Uluru) and Mount Conner (Gosse 1874). Returning again in 1873 to 1874, but approaching from the south, Giles travelled north from the Musgrave Ranges to Kata Tjuta. He then proceeded west-southwestward to Stevensons Peak and through the Olia Chain and Petermann Ranges in an attempt to nd a route westwards. This attempt failed and ended with the death of expedition member Gibson in the Western Australian desert that is now named after him (Giles 1889). In Giles’ fth expedition (1876) he again passed through the southern part of AYERS ROCK on a successful journey west from the overland telegraph line to the Indian Ocean.
Geological and geophysical investigations
The rst scienti c venture in Central Australia was the Central Australia Exploring Expedition, under the command of WH Tietkins, in 1889. This expedition travelled from Bloods Range to Mount Currie en route to Charlotte Waters on the Overland Telegraph Line. Although some rock samples were collected, only basic geological observations were made (Tietkins 1891). This was followed in 1896 by the Horn Expedition, which concentrated on the ranges to the north, although a visit was made to both Uluru and Kata Tjuta (Tate and Watt 1896). In 1903, the South Australian Government Northwest Prospecting Expedition traversed AYERS ROCK as part of an evaluation of the mineral potential of the Musgrave Block. Basedow (1905) made a series of geological observations at Kata Tjuta, Uluru and Mount Conner, and was the rst to undertake petrological descriptions of rocks, including arkose at Uluru.
In 1905-06, a Government Prospecting Expedition was despatched from South Australia to the southwestern Northern Territory to assess gold potential (George 1907). Only cursory geological observations were made. Heat and lack of water made prospecting dif cult and the expedition met with no success. Although Alice Springs was reached at the end of March 1906, George died soon afterwards on the 4th April. These explorers were followed in subsequent years by a number of bushmen and prospectors looking for mineral or pastoral opportunities. Basedow and Mackay passed through the area during 1926 with the intention of evaluating the gold potential of the Petermann Ranges. At Kata Tjuta and Mount Currie, cursory geological observations were made and Basedow (1929) noted that “the beds consist essentially of metamorphic conglomerate of Ordovician Age”.
In 1930, Michael Terry carried out a reconnaissance eld trip to the Petermann and Tomkinson Ranges and passed
4
Figure 3. Uluru
Figure 4. Kata Tjuta
Figure 5. Kelly Hills, viewed from the east (from near GS460380)
5
Mount Conner, Uluru and Kata Tjuta. He concluded that “no evidence of any mineral of commercial value exists in this area”. Thomas Blatchford, a Western Australian Government Geologist followed in 1931 and inspected Uluru and Kata Tjuta. He concluded of Kata Tjuta; “there is little doubt that the deposit has been transported and dumped by a glacier” (Ellis 1937).
The ill-fated Border Gold Reefs Ltd Expeditions of 1935 and 1936 searched for Lasseter’s Gold Reef and passed through the southern part of AYERS ROCK en route to its alleged location over the border in Western Australia. Their journey was along the informally established route, Erldunda to Mount Conner, then south into South Australia, then northeast to Gordon Hill, Stevensons Peak and the Petermann Ranges. MA Ellis, from the Western Australian Geological Survey accompanied the 1936 expedition, but only cursory geological observations were made (Ellis 1937).
Modern exploration commenced in 1959 with the Frome-Broken Hill Company embarking on reconnaissance oil exploration in the Amadeus Basin (Gillespie 1959). During 1960-61, the Institut Français du Petrole, under contract to the BMR, prepared a photogeological interpretation of the Amadeus Basin, including AYERS ROCK (Scanvic 1961). Also in 1960, the BMR flew an aeromagnetic traverse from Mount Davies to Alice Springs that passed over AYERS ROCK (Goodeve 1961). In 1962, regional gravity measurements were collected from an 11 km grid (Lonsdale and Flavelle 1963), and in 1963, two eld parties from the BMR mapped the outcrop on AYERS ROCK and produced the rst geological map of the area (Forman 1965, Wells et al 1966).
In the late 1970s, the NT Power and Water Authority3 investigated water resources by drilling over 200 exploratory holes in the Yulara-Uluru area (Read 1978, Jolly 1979, Knott 1981). In addition, the BMR has undertaken hydrological studies of the Amadeus Basin on AYERS ROCK (Jacobson et al 1988, 1989, English 1998). Other workers have investigated playa lakes (Arakel 1987), calcrete (Arakel and McConchie 1982, Arakel 1991) and gypsum deposits (Chen et al 1991, Chen 1994). Since 1961, a number of investigations have been conducted into geomorphological aspects of Uluru and Kata Tjuta (Ollier and Tuddenham 1961, Twidale 1978, Harris and Twidale 1991, Sweet and Crick 1992, Stüwe 1994).
In 1984, the Australian National University undertook teleseismic work across the Amadeus Basin with two north-south lines that ended in South Australia. The more extensive Central Australian line began north of the Ngalia Basin and passed along the Curtin Springs-Mulga Park road, whereas the shorter Musgrave line commenced at Lake Amadeus and passed along Britten Jones track (Lambeck 1991). This was followed in 1985 by a BMR deep seismic line, which crossed the Amadeus Basin from the northeast and ended near Curtin Springs (Wright et al 1991).
The NTGS collected aeromagnetic and radiometric data for the Kulgera West survey in 1986, covering BRITTEN JONES and MULGA PARK (Aerodata 1989). In 1988, the Ayers Rock survey covered MOUNT OLGA, ALLANAH and the western 35% of AYERS ROCK (Austirex 1988). In 2000, the Amadeus Central
survey covered the remainder of AYERS ROCK, except for part of the eastern Uluru-Kata Tjuta National Park. Surveys were own at 100 m altitude and 500 m line spacing, except for the Amadeus Central survey, which was own at 80 m altitude and 400 m spacing (Slater 2001). Gravity surveys have been completed by the NTGS in eastern AYERS ROCK (Simons 1990, Clifton 1994a, b) and the data have been added to the national Geoscience Australia gravity database. Geological mapping of MULGA PARK and CURTIN was carried out in 1989-90 (Camacho 1991, Young 1992) and the remaining sheets were mapped mainly between 1992 and 1995, including minor eldwork up to 1997.
Exploration activity has been con ned to investigations of the oil and gas potential within the Amadeus Basin in the northeast of AYERS ROCK. Paci c Oil and Gas completed a number of seismic lines in northern CURTIN (Menpes 1990) and drilled the dry exploratory well Murphy 1, 65 km to the east on KULGERA (Menpes 1991). In basement areas in the south, there are no known prospects or areas of mineralisation. To date, minimal significant exploration work has been reported.
REGIONAL GEOLOGICAL SETTING
Two major provinces are recognised in AYERS ROCK: a Mesoproterozoic basement complex in the south that represents the northern margin of the Musgrave Block; and Neoproterozoic to Palaeozoic sediments of the Amadeus Basin that are exposed mainly in the north. Key features of mapped units from these areas are summarised in Table 1 and Table 2 and de nitions of newly named units are given in Appendix 1. Most formations of the Amadeus Basin were de ned during the original BMR mapping program (Wells et al 1970).
The total Musgrave Block covers an area of 135 000 km2, the majority of which is in Western Australia and South Australia. In AYERS ROCK, the Musgrave Block is composed of two subdomains of granite and granitic gneiss. These are the amphibolite facies Mulga Park subdomain and the granulite facies Fregon subdomain (Camacho and Fanning 1995).
The Mulga Park subdomain covers much of southern AYERS ROCK and consists mainly of granitic rocks formed during three magmatic episodes at 1550 Ma, 1150 Ma and 1050 Ma (see Geochronology). The original crustal rocks, into which the oldest granites were intruded, are not exposed, but may be represented by ma c xenoliths within the older granitic unit, the Allanah Gneiss. Cores of zircon crystals from two samples of granitic gneiss have been dated at 1700 Ma and 2000 Ma, and may have been inherited from these earlier rocks.
The Fregon subdomain occurs in southernmost AYERS ROCK. It overlies and is separated from the Mulga Park subdomain by mylonites and ultramylonites of the Woodroffe Thrust (Camacho et al 1995). Zircon data are consistent with Fregon subdomain gneiss being 1550 Ma in age and equivalent to the Allanah Gneiss (Camacho and Fanning 1995). Metamorphism to granulite facies took place during the 1200-1170 Ma Musgravian Event. During and following
3 Now Department of Infrastructure, Planning and Environment.
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this event, the dominant 1150 Ma granites were intruded. Further granite and charnockite intrusions took place at 1050 Ma and formed the Michell Nob Granite, Nulchara Charnockite and possibly other plutons that have not been recognised within the extensive Kulpitjata Granite Complex.
During the Petermann Orogeny, the Fregon subdomain was thrust over the lower grade Mulga Park subdomain. The zone of thrusting is up to 1000 m thick and is part of the Woodroffe Thrust. It is well de ned by mylonite at the base and has a thick upper zone that contains a variable amount of pseudotachylyte. Upper greenschist to lower amphibolite facies metamorphism, which was contemporaneous with thrusting, resulted in a mylonitic fabric that variably overprinted basement rocks (Edgoose et al 1993, Camacho et al 1995, Camacho and Fanning 1995).
The Amadeus Basin (see Korsch and Kennard 1991) is a large east-west elongate intracratonic structure, which is 800 km long and 300 km wide. It extends across the western two-thirds of the southern Northern Territory into Western Australia, and contains up to 14 km of Neoproterozoic
and Palaeozoic sediments (Shaw 1991). The Amadeus Basin succession has been correlated with those in the Ngalia and Georgina Basins (Preiss et al 1978) and with that in the Of cer Basin (Zang 1995). Walter et al (1995) proposed the existence of a large superbasin, based on these stratigraphic similarities. Lindsay and Korsch (1991) recognised two periods of complex extensional events and thermal recovery within the Amadeus Basin. Shaw et al (1991) suggested that the basin was sensitive to changing forces acting at the scale of the continental plate.
The two earliest sedimentary units of the Amadeus Basin, the Dean Quartzite and Pinyinna beds (siltstone and dolostone), were deposited at about 830 Ma over part of the Musgrave Block basement. Further marine sedimentation took place in the Neoproterozoic and formed the Bitter Springs Formation (dolostone and evaporite; a lateral equivalent to the Pinyinna beds), Inindia beds (sandstone, siltstone and chert) and Winnall beds (sandstone and siltstone). Coarse uvial sediments (Mount Currie Conglomerate and Mutitjulu Arkose) were deposited in small sub-basins during the Petermann Orogeny, and were followed by
Table 1. Rock units of the Musgrave Block in AYERS ROCK, excluding rocks dominated by mylonite and pseudotachylite generated in the Petermann Orogeny; 1Glikson et al (1996); 2Zhao and McCulloch (1993)
UNIT, MAP SYMBOL AND LITHOLOGY DISTRIBUTION COMMENTS, AGE
MESO- TO NEOPROTEROZOICDolerite Dykes (LPdl)
Fine to medium with ophitic texture Widespread throughout basement areas
May include three generations, correlated with Alcurra dyke swarm (1080 Ma), Tollu Group (1078 ± 5 Ma1) and Amata dykes (824 ± 4 Ma2)
MESOPROTEROZOIC POST-MUSGRAVIAN EVENT GRANITES Michell Nob Granite (LPgm)
Coarse, porphyritic, garnet- and hornblende-bearing biotite granite with mylonitic fabric
Nulchara Charnockite (LPgn) Medium to coarse, weakly to strongly porphyritic orthopyroxene granite, generally non-foliated
Restricted to southeast
Restricted to southeast
Topographically overlain by Nulchara Charnockite. No clear field evidence as to order of intrusion. Dated at 1068 ± 6 Ma
Topographically overlies Michell Nob Granite. No clear field evidence as to order of intrusion. Dated at 1044 ± 5 Ma
Kulpitjata Granite Complex (LPgk)Includes Yununba and Katiti Granites. Biotite granite and mylonitized equivalents. Fine to coarse, less commonly megacrystic. In places, equigranular, more commonly porphyroblastic in sheared rocks. Lesser hornblende-biotite granite, pegmatite and aplite
Widespread throughout basement areas
Zircon crystallization ages in the range 1197-1150 Ma; inherited 1550 Ma cores. Contains xenoliths of Allanah Granitic Gneiss and intrudes Kelly Hill Beds
Musgravian Event (1200-1170 Ma)
Opparinna Metamorphics (LPop) Thin sequence of andalusite schist, quartzite and amphibolite Restricted to
southwestern Kelly Hills in BRITTEN JONES
Intruded by dykes of Kulpitjata Granite Complex and pegmatite; hence older than 1150 Ma. Quartzite carries a single age population of zircons, 1603 ± 36 Ma
Syn-granite metamorphism (1550 Ma suggested by Camacho 1997)
Felsic Granulite Facies Gneiss (LPfg) Medium quartzofeldspathic gneiss (mainly granitic), metamorphosed to granulite facies, contains pseudotachylite adjacent to thrust plane
Occurs in south, above Woodroffe Thrust
Precursor age 1563 Ma; correlated with Allanah Gneiss by Camacho and Fanning (1995)
Allanah Gneiss (LPnga) Banded, fine to medium quartzofeldspathic gneiss, migmatitic Infrequent small
exposures and xenoliths scattered through basement outcrop area in the south
Crystallization age of gneiss precursor 1590-1539 Ma. Inherited zircon cores of 2000 Ma and 1700 Ma
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Table 2. Stratigraphy of the Amadeus Basin in AYERS ROCK
UNIT, MAP SYMBOL AND LITHOLOGY DISTRIBUTION FIELD RELATIONSHIP DEPOSITIONAL ENVIRONMENT
DEVONIAN Horseshoe Bend Shale (Dh)
Interbedded micaceous shale, siltstone, rare fine sandstone
Limited area in northeast, north of Curtin Springs
Overlain by Cenozoic sediments; lower contact not observed
Lacustrine and fluvial
ORDOVICIAN Carmichael Sandstone (Oc)
Quartz sandstone, clayey, minor silty sandstone and siltstone, minor pebble horizons including chert; crossbeds, ripples and pseudomorphs after halite
Restricted to northeast; ridge-forming
Conformably overlies Stokes Siltstone
Shallow marine to fluvial
Stokes Siltstone (Ot) Kaolinitic and micaceous quartz sandstone, and minor interbedded dolomitic siltstone and dolostone; fossiliferous
Restricted to northeast, recessive
Conformable on Stairway Sandstone.
Shallow marine
Stairway sandstone (Os) Medium to coarse quartz sandstone, interbeds of fine kaolinitic sandstone and siltstone, occasional pebble conglomerate layers; bioturbated; contains some phosphatic pellets
Restricted to northeast; ridge-forming
Unconformable on Inindia Beds
Shallow marine
NEOPROTEROZOIC TO CAMBRIAN Multitjulu Arkose (LPzm)
Arkose; dominantly coarse but ranges from poorly sorted with fine pebble conglomerate horizons to fine and well sorted; multidirectional crossbedding, scour and fill troughs and ripples
Only known from type area at Uluru; restricted to small sub-basin
Lower and upper contacts not observed
Fluvial
Mount Currie Conglomerate (LPzc) Cobble to boulder conglomerate, oligomictic at base with clasts of Winnall Sandstone; polymictic above with clasts of rhyolite, dacite, granite and basalt
Widespread in northwest
Unconformable on Winnall Sandstone; upper contact not observed
Fluvial, high-energy environment
NEOPROTEROZOIC
Winnall Beds (LPuw) Interbedded quartz sandstone (white to brown, micaceous or clayey in part) and siltstone, which may be dolomitic or calcareous; shallow water features
Ridge-forming in north
Lies unconformably on Inindia Beds; contact not seen in AYERS ROCK; overlain unconformably by Mount Currie Conglomerate
Shallow marine to fluvial
Inindia Beds (LPun) Dominantly quartz sandstone, kaolinitic, strongly ferruginized in part; subordinate siltstone, chert and jasper, "tillite" and dolomitic limestone
Ridge-forming, restricted to northeast; interpreted from water drillholes in vicinity of Uluru
Disconformably overlies Bitter Springs Formation; overlain unconformably by Winnall Beds
Varied; shallow to deep water marine and fluvial
Basic volcanic rocks Porphyritic basalt and dolerite in upper part of Bitter Springs Formation; only known from drill core
Porphyritic basalt to the west of Curtin Springs; dolerite in vicinity of Uluru
Porphyritic basalt appears to be conformable with Bitter Springs Formation; dolerite appears to crosscut Bitter Springs Formation
Porphyritic basalt is dated at 800 Ma (Zhao et al 1994);dolerite is intrusive of same age
Bitter Springs Formation (LPub) Dolostone, evaporite-rich at base, stromatolitic at top; minor limestone and chert
Restricted to cores of anticlines in northeast and drillholes near Yulara
Conformable on Dean Quartzite
Shallow marine to terrestrial
Pinyinna Beds (LPui) Micaceous siltstone, minor kaolinitic sandstone Interfolded with Dean
Quartzite in southeast Conformable on Dean Quartzite; possible lateral equivalent of Bitter Springs Formation
Lacustrine to shallow marine
Dean Quartzite (LPud)Quartzite, sericitic at base, kaolinitic in part; phyllitic interbeds; rare crossbeds and ripples
Widespread in south and southwest
Lies unconformably on crystalline basement; tightly folded and repeated by thrusting
Shallow marine
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continued marine sedimentation during the Ordovician. The Petermann Orogeny strongly affected the Dean Quartzite and Pinyinna beds, interthrusting them with basement rocks and causing metamorphism to amphibolite facies in places (see also Scrimgeour et al 1999). The Devonian to Carboniferous Alice Springs Orogeny also caused signi cant deformation (Shaw 1991). Tingate (1990) provided apatite ssion track data to constrain uplift ages for Amadeus Basin rocks.
MUSGRAVE BLOCK
FREGON SUBDOMAIN
Felsic granulite gneiss (LPfg)
This Mesoproterozoic unit consists of homogeneous layered quartzofeldpathic gneiss, which has been metamorphosed to granulite facies. It outcrops as moderate to high hills covered by sparse vegetation and thin soil cover. The gneiss is light to dark grey, ne to medium, equigranular and felsic. It is mainly granitic in composition and contains orthopyroxene as the main ma c mineral. Small-scale sedimentary layers and structures have been overprinted, but large-scale compositional layers, up to 50 m thick, are interpreted to represent primary lithological layering (S0). These rocks may have originally been interlayered peraluminous felsic volcanics and greywackes, possibly associated with contemporaneous granite and ma c intrusions (Camacho and Fanning 1995).
Further south in WOODROFFE, Camacho (1997) reported a high proportion of felsic granulite gneiss containing quartz, K-feldspar, garnet and plagioclase + magnetite ± biotite ± spinel within this unit. Chemical compositions are peraluminous, which is consistent with a sedimentary origin, and some outcrops contain cordierite and sillimanite. However, peraluminous gneiss is minor in AYERS ROCK and is subordinate to granitic gneiss and to intermediate orthopyroxene-bearing gneiss.
Camacho and Fanning (1995) correlated the felsic granulite gneiss with amphibolite facies granitic gneiss of the Mulga Park subdomain, here named the Allanah Gneiss. The granulite gneiss is thought to have undergone the same deformations as the Allanah Gneiss during the Musgravian Event at 1200 Ma, although the metamorphic grade was higher and reached granulite facies. A sample of granulite facies gneiss (BJ96/280), from GS408564 to the north of Kelly Hills, has been dated at 1563 ± 22 Ma and has 1135 Ma metamorphic rims (see Geochronology). These dates are similar to those for granulite gneiss sample S5 from KULGERA, which is also from the Fregon subdomain (Camacho and Fanning 1995).
Granulite gneiss has been thrust over deformed granite and amphibolite facies rocks in southern AYERS ROCK. A zone of mylonite beneath the granulite gneiss represents the Woodroffe Thrust and separates these rocks from underlying granites of the Mulga Park subdomain. Pseudotachylyte veins that were formed during thrusting at the time of the Petermann Orogeny are common in this unit and have been described in detail by Camacho et al (1995).
Nulchara Charnockite (LPgn)
This igneous charnockite (pyroxene-bearing granite) is restricted to the southeast of AYERS ROCK and outcrops as resistant hills. It forms a low-angle sheet that at one location (GS733215) topographically overlies the Michell Nob Granite. There is no clear eld evidence as to the order of intrusion (Camacho 1997), but the age of the Nulchara Charnockite is younger than that of the Michell Nob Granite (see Geochronology). The charnockite is dark grey to green when fresh, medium to coarse, and weakly to strongly porphyritic. Weathered tors are darker than other granites in the area. The charnockite is mostly unfoliated, apart from a shallowly dipping foliation that becomes stronger close to the contact with the underlying Michell Nob Granite. Camacho (1997) interpreted this as a ow foliation.
The charnockite contains perthitic K-feldspar phenocrysts up to 5 cm long that carry a variety of inclusions including zircon, magnetite, ilmenite, apatite and clinopyroxene. The K-feldspar is dark green, euhedral and elongate to equant. It has embayed margins and in places is rimmed by plagioclase (rapakivi texture) and myrmekite. Smaller phenocrysts of subhedral plagioclase and lesser subrounded quartz are up to 1 cm across. The unzoned plagioclase is dusted with ne opaques and exhibits multiple twinning and antiperthitic exsolution. The groundmass is medium-coarse and contains equant K-feldspar, plagioclase, quartz, and ma c clots of clinopyroxene, orthopyroxene, hornblende and biotite. Accessory apatite, zircon, magnetite and ilmenite also occur. Hornblende occurs as granoblastic aggregates of equant crystals, and as rims on clinopyroxene. Orange-brown biotite is present in minor quantities and most commonly replaces hornblende and black opaque iron oxides. The texture is granoblastic and considered to be of igneous origin (Camacho 1997).
Camacho (1997) reported a SHRIMP U-Pb zircon date of 1044 ± 5 Ma for a sample of Nulchara Charnockite.
Mylonite and pseudotachylyte (LPm)
This unit is found in major low-angle thrust planes in the south of AYERS ROCK. Mylonitised granite and gneiss occur in the lower part of the thrust planes, whereas granulite facies felsic gneiss, which is cut by abundant pseudotachylyte veins, occurs above the thrust (Figure 6). Camacho (1989, 1997) and Camacho et al (1995) provided detailed descriptions of the rock types of thrust zones.
MULGA PARK SUBDOMAIN
Older Units
Allanah Gneiss (LPnga)
The Allanah Gneiss is a non-porphyritic, ne to medium granitic gneiss, which is migmatitic in places. It was metamorphosed to amphibolite facies during the 1200 Ma Musgravian Event. The Allanah Gneiss is exposed in many places in southern AYERS ROCK, sometimes as large outcrops, but more commonly as rafts or xenoliths within younger and more voluminous granite. It is dark grey on
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fresh surfaces and typically contains biotite and muscovite. Exposures vary from low to rounded hills that contain prominent tors and pavements.
This unit includes rocks previously mapped by Camacho (1991) as Mulga Park Gneiss in MULGA PARK, as well as outcrops designated as amphibolite facies gneiss in generalised maps by Camacho and Fanning (1995) and Camacho et al (1995). It is also possible that granitic gneiss of the former Mulga Suite in MULGA PARK (Camacho 1991) may correlate with the Allanah Gneiss. However, these outcrops have been shown on the map as undivided granite and gneiss because of uncertainty about whether their gneissic fabric is due to the Musgravian Event or to the Petermann Orogeny.
Gneissic layering in the Allanah Gneiss probably resulted from deformation during the Musgravian Event. In places, it is strongly overprinted by zones of a younger intense mylonitic fabric, which was associated with the Petermann Orogeny. The gneissic fabric in some outcrops appears to be quite planar, although in places, there is some open to tight folding of the fabric. Many outcrops have undergone partial melting and are variably migmatitic (Figure 7). In some outcrops (eg MP43 at GS821222), leucosome veins cut the gneissic foliation and are commonly subparallel to later upright fold axes. Minerals within the gneiss include quartz, K-feldspar, plagioclase, biotite and garnet. Crystallisation of new grains of garnet, muscovite, sphene and epidote is con ned to these zones.
Minor components of the Allanah Gneiss include small lenticular bodies of black-green, ne to medium amphibolite and pelitic gneiss in southern MULGA PARK. The pelite contains quartz, K-feldspar, plagioclase, garnet, biotite and muscovite. Alternating bands of migmatitic veins and biotite-rich layers de ne the foliation within the pelite, which is generally weathered in outcrop.
Two samples of Allanah Gneiss yielded a range of U-Pb zircon dates from 1591-1539 Ma and this is probably the age of igneous crystallisation. One sample has a 1206 Ma zircon rim, and this probably represents the age of gneissic
deformation and amphibolite facies metamorphism during the Musgravian Event. Both samples have older zircon cores: MP43 has one core at approximately 2000 Ma and A94/1378 has cores at approximately 1700 Ma (see Geochronology).
Basement quartzite (LPq)
Well layered, foliated outcrops of quartzite are intercalated with coarse granite, pegmatite, quartz-mica schist and lesser amphibolite. They are probably remnants of an older basement sequence within the Kulpitjata Granite Complex. The basement quartzite in southeastern AYERS ROCK forms ridges up to 30 m high and low outcrops that are partially covered by sand. In thin section, the quartzite has a granoblastic texture of quartz and minor muscovite, garnet, biotite, opaques and plagioclase.
Opparinna Metamorphics (LPop)
The Opparinna Metamorphics are restricted to the southwestern margin of Kelly Hills in southeastern AYERS ROCK. They dip to the east at 15° and comprise a lower (assuming no overturning) andalusite schist, overlain by quartzite and then by conformable meta-igneous amphibolite.
Camacho and Fanning (1995) rst described the unusual mineralogy of these metamorphics. Andalusite schist occurs as a layer up to 30 m thick that overlies sheared granitic gneiss of the Kulpitjata Granite Complex. The schist contains muscovite, quartz, viridine4 and opaques. Muscovite is straw coloured and occurs as subparallel lamellae and disseminated akes. Fine opaques and anhedral irregular viridine are generally associated with the lamellae. Viridine comprises up to 15% of examined thin sections and occurs as medium to coarse, strongly poikilitic porphyroblasts and as ne anhedral grains located at the margins of quartz grains. The porphyroblasts have highly irregular margins and numerous inclusions of very ne quartz, muscovite and black opaques in parallel sigmoidal trails.
Figure 6. Pseudotachylite veins cutting granulite gneiss in low-angle thrust plane in southern AYERS ROCK (GS640270)
4 Green, Mn-rich andalusite.
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A resistant quartzite overlies the andalusite schist and has a maximum thickness of 15 m. It is strongly foliated, but relict bedding is visible. It contains quartz, muscovite, opaques, and accessory euhedral spessartine garnet and anhedral piemontite. Traces of microcline and zircon are present.
Amphibolite occurs in the Opparinna Metamorphics as a 50 m thick body that is interleaved with the underlying quartzite. It was derived from a protolith of basalt or dolerite. The amphibolite is dark grey to green, massive, ne and equigranular. It is composed mainly of hornblende, lesser plagioclase, minor quartz and titanite, and accessory opaques, pyrite and apatite.
Coarse granite and pegmatite dykes intrude all rock types and are mainly sub-parallel to layering and foliation. These dykes are probably part of the Kulpitjata Granite Complex and this indicates that the metamorphics are older than 1150 Ma, which is the minimum age of crystallisation of the granite complex. A U-Pb isotopic study of quartzite (sample BJ75, GS416289) found a single zircon population at 1603 ± 36 Ma. No younger ages were obtained. This provides a maximum age for the metamorphics.
Undivided granite and gneiss (LPgu)
This unit is applied to outcrops formerly mapped as “Mulga Suite” (Camacho 1991) in MULGA PARK. It consists of medium, non-porpyritic granitic gneiss that contains biotite and muscovite. It is not certain whether the gneissic fabrics are due to the Musgravian Event or to the Petermann Orogeny, and hence these rocks may correlate either with the Allanah Gneiss or the Kulpitjata Granite Complex.
Kulpitjata Granite Complex
This extensive unit consists mainly of biotite granite (Figures 8-11), sheared derivatives (mylonitic granitic gneiss and schist), plus lesser hornblende granite, aplite, pegmatite, granitic dykes and quartz veins. It includes two formal units in MULGA PARK, the Yununba Granite and Katiti Granite (Camacho 1991). The majority of outcrops
mapped as the Kulpitjata Granite Complex are probably about 1150 Ma in age, but due to incomplete access and a strong deformational overprint in places, it is possible that our mapping of the unit has included some areas of older or younger granitic material (eg 1550 Ma Allanah Gneiss or 1050 Ma granites). Outcrops of this complex in western AYERS ROCK may correlate with the Mantarrur Suite of Scrimgeour et al (1999).
SHRIMP U-Pb zircon isotopic work has provided a range of dates from 1197-1150 Ma and these are interpreted as the age of igneous crystallisation (see Geochronology). Several samples have zircon with older inherited cores that were dated at around 1550 Ma.
Yununba Granite (LPgky)
The strongly foliated Yununba Granite was described by Camacho (1991) from MULGA PARK. Although similar to the undifferentiated Kulpitjata Granite Complex, it is retained as a separate unit. It comprises medium, variably porphyritic granite, grading to coarse, strongly porphyritic granite. It is typically grey to white on fresh surfaces and contains crystals of elongate white K-feldspar up to 2 cm long, and plagioclase and quartz up to 1 cm across. The groundmass contains quartz, feldspars, biotite, secondary muscovite, and accessory apatite, zircon, magnetite, ilmenite, allanite and sphene. Fluorite occurs in places, as does metamorphic garnet.
Aplite and pegmatite dykes occur in places, but are uncommon. Late joints cut the foliation and in places are lled with epidote. The foliation is mylonitic and de ned by a penetrative, shallowly dipping, anastamosing schistosity that in places wraps around lower strain boudins up to 30 m across. A sample of the Yununba Granite was dated at 1159 ± 20 Ma (Camacho and Fanning 1995).
Katiti Granite (LPgkk)
This granite is located in MULGA PARK. It is grey to pink when fresh, medium-grained, porphyritic and has a strong
Figure 7. Gneissic layering in Allanah Granitic Gneiss (GS819224)
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mylonitic fabric de ned by thin anastamosing bands of green biotite (Camacho 1991). Porphyroblasts of K-feldspar up to 3 mm across remain within the fabric and are relict magmatic grains. In high strain zones, plagioclase is extensively altered to ne, randomly oriented muscovite, epidote and green biotite. Accessory amphibole, apatite and zircon occur within biotite-rich bands. A deformed, iron-rich and sul de-bearing sample gave a U-Pb evaporative zircon age of 1172 ± 4 Ma (see Geochronology).
Undivided Kulpitjata Granite Complex (LPgk)
The Kulpitjata Granite Complex forms a northwest-trending belt in southern AYERS ROCK of low, rugged, sparsely vegetated hills and small, rounded bare hills, tors and pavements. More prominent hills within this belt have a cap of Dean Quartzite. Between these hills and elsewhere through the plains, isolated tors and pavements occur within a thin cover of alluvium. The main rock type is biotite granite, but hornblende granite also occurs. A deformational overprint varies from rare undeformed granite through to strongly deformed and mylonitic granitic gneiss and schist. In places, the granites carry ma c to intermediate enclaves or xenoliths, as well as xenoliths of Allanah Gneiss, quartzite, hornblende-biotite granite, and metagrabbro. These rock types are crosscut by pegmatite and medium-grained aplite dykes, and by quartz veins.
Biotite granite and deformed granite
Biotite granite varies from light-medium grey where fresh to red-grey where weathered. The rock is ne to coarse and weakly to strongly megacrystic. This granite and deformed equivalents contain the primary minerals K-feldspar, quartz, biotite and plagioclase. Accessory minerals include zircon, opaques and apatite and in some rocks, hornblende, allanite and uorite. Secondary metamorphic minerals include muscovite, garnet, sphene, epidote, haematite and chlorite.
K-feldspar is present as small anhedral grains and coarse subhedral to euhedral phenocrysts and megacrysts up to 30 mm across in the augen gneisses. All grains exhibit irregular corroded margins, especially where they are in contact with ne-grained matrix in shears. Areas of myrmekitic texture are developed at some grain margins and are probably associated with deformation. Inclusions of corroded and altered K-feldspar and plagioclase, rounded quartz, needle-like euhedral epidote, biotite, anhedral to euhedral sphene and chlorite are present. Within the larger ovoid K-feldspar phenocrysts and megacrysts, small biotite inclusions may be present in a pattern of concentric rings. Sericite alteration is common and epidote and calcite are also present. In rock sample A94/519 (FS566663), laths of green amazonite are present.
Quartz is recrystallized, generally elongate and ne-grained. Biotite varies from being an accessory mineral to 12%. In weakly deformed granite, the biotite is disseminated, but has a weak subparallel orientation. Biotite-rich layers occur in strongly deformed granite. Garnet is present (maximum 3%) in disseminated subhedral to euhedral grains that commonly have numerous inclusions. Other accessory minerals include uorite, black opaques, subhedral to euhedral allanite (in places rimmed by sphene) and hornblende as anhedral or corroded crystals. Traces of apatite, zircon and chlorite (as an alteration product) are present.
Moderately deformed granite is characterised by K-feldspar augen set within semicontinuous felsic and ma c segregation bands. Strongly deformed granite is characterised by stretched K-feldspar augen set within more continuous, planar, parallel felsic and ma c segregation bands. Both types feature S-C fabrics.
Intense deformation occurs in thin (1-3 m thick) protomylonite zones within some granite outcrops. Mylonite zones are common in southeastern ALLANAH, where they occur at the bases of hills and inselbergs and are parallel to a generally at-lying or gently dipping foliation. Mylonite zones have resulted in the formation of grey, medium-grained muscovite-biotite-quartz schist, in extreme cases of which feldspars have been converted to mica.
Figure 8. Medium megacrystic granite in undivided Kulpitjata Granitic Complex (GS376617)
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Hornblende granite
Hornblende granite is relatively common in southeastern ALLANAH. It occurs as 100 m wide zones within biotite granite and as xenoliths elongated parallel to the foliation (eg rock sample A93/191 from FS882347). Elsewhere on AYERS ROCK, it is uncommon and occurs in outcrops generally too small to differentiate on the map.
Hornblende granite is grey to very dark grey, medium to ne and typically equigranular, but occasionally it is weakly porphyritic and has simply twinned phenocrysts of K-feldspar. Contacts with biotite granite are generally sharp. Hornblende granite is moderately to strongly foliated and in places has a strong lineation. The major minerals are K-feldspar, quartz, hornblende, biotite, plagioclase and opaques. Accessory minerals include sphene, epidote, apatite, chlorite and zircon.
Aplite
Aplite dykes, which are generally less than 40 cm wide, intrude the Kulpitjata Granite Complex. They are ne-grained equigranular and felsic. Short, thin elongated patches of ma c minerals highlight a weak foliation, consistent with the enclosing deformed granite.
Pegmatite
Pegmatitic dykes are found with varying frequency within deformed granite. They also form boudins up to one metre wide, parallel to the foliation. They are quartz-rich, contain a variable amount of subhedral to euhedral K-feldspar and may carry small books of biotite or rare muscovite to 5 cm, plus some ilmenite and magnetite. Fluorite and deformed coarse euhedral tourmaline were recognised in pegmatite from ALLANAH.
Figure 9. Medium granite in undivided Kulpitjata Granitic Complex (FS892387)
Figure 10. Coarse granite in undivided Kulpitjata Granitic Complex (FS578526)
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Quartz veins
Quartz veins within the Kulpitjata Granite Complex are associated with granite magmatism and are also probably related to the Petermann Orogeny. Veins associated with granite magmatism are parallel to the foliation and generally 2-5 m wide. The quartz is white and massive and may show a faint foliation parallel to that in the enclosing granite. The quartz veins only rarely carry ilmenite or magnetite. Veins related to the Petermann Orogeny are generally thinner (<1 m), unfoliated and crosscut the foliated granite.
Younger Igneous Rocks
Michell Nob Granite (LPgm)
This granite is exposed in a small area to the south of Mulga Park Station along the SA-NT border. Camacho (1997) reported further outcrops in South Australia. It forms smooth rounded inselbergs and at one locality (GS733215) is overlain by the Nulchara Charnockite, which has yielded a younger U-Pb age (see Geochronology). However, There is no clear eld evidence as to the order of intrusion (Camacho 1997).
The Michell Nob Granite is coarse and porphyritic. It contains primary K-felspar, plagioclase, quartz, biotite, garnet and amphibole plus accessory sphene, epidote, apatite, zircon, magnetite and ilmenite. Large (up to 3 cm) simply twinned crystals of K-feldspar are present. A strong anastomosing mylonitic fabric wraps around coarse K-feldspar augen. The fine mylonitic matrix consists of recrystallized quartz, K-feldspar, palgioclase and elongate clots of biotite and hornblende. Biotite and hornblende de ne a mineral elongation parallel to the stretching lineation. Shear zones range from a few mm to 1 m in width and have a steep stretching lineation. Plagioclase contains inclusions of euhedral epidote. A SHRIMP U-Pb zircon date of 1068 ± 6 Ma was interpreted as an igneous crystallisation age by Camacho (1997).
Dolerite dykes and gabbro (LPdl)
On AYERS ROCK, thin dolerite dykes most commonly intrude the Kulpitjata Granite Complex in BRITTEN JONES. They occur either individually or in swarms that are parallel or subparallel to foliation. The dolerite generally is massive, ne to medium and dark green to black. Metagabbro occurs as dark blocky outcrops that intrude granite in southern ALLANAH.
Some dolerite dykes are correlatives of the 1080 Ma Alcurra dyke swarm (Zhao and McCulloch 1993, Edgoose et al 1993). These dykes are tholeiitic and range from pristine to strongly altered. They have ophitic textures and contain plagioclase, clinopyroxene (titanaugite), olivine and opaques. Chlorite alteration products and secondary calcite are present, expecially in ne dolerite.
Other ma c dykes and a metagabbro (A93/121, FS829321) are correlated with the Mummawarrawarra Basalt of the 1078 ± 5 Ma Tollu Group (Glickson et al 1996, Sheraton and Sun 1997, see Geochemistry). These are more siliceous and potassic than the Alcurra dolerites and have clinopyroxene and plagioclase as phenocrysts, plus a distinctive granophyric texture in the groundmass. Opaques include magnetite and pseudomorphs after magnetite plus pyrite and pseudomorphs after pyrite. Apatite is present in trace amounts as small needles within feldspars. Secondary epidote is also common in metagabbro.
Younger dolerite dykes were recognised in PETERMANN RANGES and were correlated by Scrimgeour et al (1999) with the 820 Ma Amata dyke swarm in South Australia (Zhao and McCulloch 1993). No Amata dolerite dykes have been recognised in AYERS ROCK, although ma c intrusions and volcanics within the Bitter Springs Formation may correlate with this episode of ma c magmatism (Zhao et al 1994).
Amphibolite (LPam)
Amphibolite occurs mainly within granite in AYERS ROCK and forms thin elongate bodies parallel to the foliation. These are metamorphosed dykes, generally only a few metres wide and up to several hundred metres long. Only rarely do
Figure 11. Mylonitised granite containing relict feldspar porphyroblasts in undivided Kulpitjata Granitic Complex (FS750536)
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irregular, wider bodies occur. At some localities, amphibolite bodies are complexly folded and may be boudins or xenoliths in the Kulpitjata Granite Complex. The amphibolite represents either a syn-granite phase of ma c magmatism, or Alcurra dolerite dykes that were metamorphosed during the Petermann Orogeny.
The amphibolite is dark greenish-black and is ne-grained. A foliation is de ned by the preferred orientation of elongate hornblende and biotite, and a strong continuous gneissic banding is also recognisable in places. Major minerals include hornblende, plagioclase, quartz and black opaques. Epidote and biotite are accessory minerals and zircon and titanite occur in trace amounts. Minor sericitic alteration is present. The opaques are probably magnetite and pseudomorphs after magnetite, and occur as disseminated grains and inclusions. Fine euhedral cubic grains of pyrite? were observed within hornblende in one thin section.
AMADEUS BASIN
Dean Quartzite (LPde)
The Dean Quartzite (Figure 12) occurs in southwestern AYERS ROCK, where it forms prominent ridges and escarpments. It is thinly to thickly bedded and typically consists of massive, clean white quartzite, lesser schistose sericitic quartzite and conglomerate in places at the base. The unit unconformably overlies basement gneiss and granite, and the contact may be strongly sheared. In AYERS ROCK, the formation is typically 30-50 m thick, but many sheared exposures are less than 30 m thick. At Mount Gordon in southwestern AYERS ROCK, the Dean Quartzite reaches 200 m in thickness, due to structural repetition. Many exposures of the Dean Quartzite have been isoclinally folded and are repeated by thrusting. Some exposures contain phyllite layers that have the appearance of interbeds, but similar outcrops in PETERMANN RANGES were interpreted as Pinyinna beds that have been interthrusted with the Dean Quartzite (Scrimgeour et al 1999).
The Dean Quartzite (Wells et al 1964, Forman 1966) and its correlative in the north, the Heavitree Quartzite (Lindsay 1991), are the oldest preserved sedimentary units in most parts of the Amadeus Basin. Correlation of the two is based upon their stratigraphic position and upon lithological similarities. These quartzites and the slightly younger Bitter Springs Formation form a continuous sheet within the Amadeus Basin and were deposited over a large area that extends beyond the present margins of what is essentially a structural basin (Wells et al 1970). The Dean Quartzite is undated, but Lindsay (1999) suggested an age of 800-760 Ma for the equivalent Heavitree Quartzite.
Generally, the Dean Quartzite consists of clean white orthoquartzite, but in the vicinity of shear zones, this may be dark grey in colour. Rare cubic voids are possibly after halite. An elevated sericitic content at the base is interpreted as re ecting the original clay matrix of the quartzite. At the base and in bands above the base, a coarser rock-type occurs that may be a granule conglomerate with deformed stretched pebbles. A similar basal rock unit in PETERMANN RANGES was interpreted as being Bloods Range beds (Scrimgeour et al 1999). Tight folds that have axial planes parallel to bedding also occur near the base of the Dean Quartzite.
In thin section, quartz is dominant and accessory muscovite de nes the foliation. Trace quantities of kyanite, spinel, zircon, black opaques and tourmaline? are present in some locations. Fine-grained sheared horizons contain quartz, muscovite, opaques, zircon, allanite, tourmaline, spinel and epidote. The presence of metamorphic kyanite indicates that parts of the Dean Quartzite have been subjected to high pressures (see also Scrimgeour et al 1999). Lindsay (1991) recognised burrow-like structures similar to Skolithos from the Heavitree Quartzite in the northeastern Amadeus Basin and this is consistent with a shallow marine or tidal depositional setting.
Pinyinna beds (LPi)
The Pinyinna beds conformably overly the Dean Quartzite and occur in southern AYERS ROCK as a 10-20 m thick sheared
Figure 12. Tight folds in outcrop of Dean Quartzite (FS847395)
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phyllitic unit that is rarely exposed. This unit is a lateral equivalent of the Bitter Springs Formation, but a separate name is justi ed, as the phyllite is distinct from dolostone assigned to the Bitter Springs Formation in northeastern AYERS ROCK.
The type area is Pinyinna Range in BLOODS RANGE, where Forman (1966) reported 245 m of grey, brown and white laminated micaceous siltstone. Elsewhere, the unit is interbedded with crystalline dolostone and limestone. In AYERS ROCK, the phyllitic foliation is parallel to the prevailing mylonitic fabric within the Dean Quartzite and granitic basement. Phyllite has acted as a décollement during thrusting associated with the Petermann Orogeny and mostly occurs as interlayers with Dean Quartzite and granite in thrust duplexes. Read (1978) identi ed phyllitic material from water bores east of Kata Tjuta as Pinyinna Beds. He interpreted these strata as having been thrust over the Mount Currie Conglomerate during the Petermann Orogeny.
Bitter Springs Formation (LPbi)
The Bitter Springs Formation outcrops extensively within the limits of the Amadeus Basin. Joklik (1955) originally named the thick sequence of mainly dolostone, dolomitic siltstone and evaporitic rocks that conformably overlies the Heavitree Quartzite in the northeastern Amadeus Basin as the Bitter Springs Limestone. Wells et al (1967) revised the name to Bitter Springs Formation and divided it into the Gillen and Loves Creek Members. Dolostone and evaporites are the main rock types in the Gillen Member, whereas the overlying Loves Creek Member contains a greater proportion of dolomitic siltstone and stromatolitic dolostone.
In AYERS ROCK, the formation is exposed in the core of an anticline in two locations to the northwest of Curtin Springs, where it forms low hills that are partially masked by calcrete or aeolian sand. These exposures form part of an extensive sheet deposit, which is largely concealed beneath Cenozoic sediments, but which reaches a thickness in excess of 130 m, as determined from water drillholes adjacent to Yulara. North of Curtin Springs, exposures of the formation consist of monotonous grey to brown thinly bedded dolostone with occasional thin veins of calcite that are oriented parallel to bedding. Elsewhere, the unit is composed of grey dolostone, as determined from drillhole cuttings. The lower contact is not observed, but the unit is assumed to be conformable on the Dean Quartzite. The Stairway Sandstone unconformably overlies the formation in Curtin.
The thickness of the formation is dif cult to determine from surface outcrop, but can be estimated from oil wells. In KULGERA, the drillhole Erldunda 1 intersected 350 m of Bitter Springs Formation, which consisted of dolostone, sandstone and siltstone. Gypsum and halite became more common as depth increased (Pemberton and McTaggart 1966). Drillhole Murphy 1 in central KULGERA intersected 1650 m of a similar sequence, the lower 840 m of which consisted of halite and anhydrite. This hole was completed at 2879 m without encountering Dean Quartzite at the base and a re-evaluation of seismic results after completion of
the hole suggested that the contact was 500-1000 m below the completion depth (Menpes 1991). Wells et al (1970) considered the Gillen and Loves Creek Members to be conformable. However, evidence from Paci c Oil and Gas seismic surveys and from Murphy 1 suggested the existence of an angular unconformity between these units (Menpes 1991). An erosional surface between the members that was detected by Magellan Petroleum in the northeastern Amadeus Basin was interpreted by Southgate (1991) to be a disconformity.
In the Dune Plains bore eld to the south of Yulara, water bore cuttings indicate that the Bitter Springs Formation consists mainly of grey to brown dolostone. However, the high sulfate content of water from some boreholes also suggests the presence of evaporite minerals (Read 1978 and unpublished water bore logs examined by N Duncan). Cores containing Bitter Springs Formation were recovered from the 1981 BMR drillholes Ayers Rock 1 and 2, which were designed to test small but intense aeromagnetic anomalies (Bladon and Davies 1982). Beneath Cenozoic cover, approximately 40 m of porphyritic basalt was encounted and this appeared to be conformable on Bitter Springs Formation sedimentary rocks. Bladon and Davies reported that these rocks consisted of light grey to black indurated microcrystalline dolostone (possibly stromatolitic in part) that was interbedded with finely crystalline dolomite, minor limestone, chert and gypsiferous microcrystalline dolostone.
Wells et al (1967) proposed that the cyclical repetition of lithologies within the Bitter Springs Formation indicates an alternation of depositional environments, particularly water depth. Menpes (1991) interpreted a stable, shallow marine evaporitic environment. Isotopic C13 analyses carried out on cutting samples of subsurface Bitter Springs Formation5 in the Dune Plains Bore eld area and in areas adjacent to Uluru have been used to determine depositional environments in these areas (A Hill, Macquarie University, pers comm 1996). A sample from drillhole RN7001 indicated a shallow marine, stromatolitic environment consistent with the Loves Creek Member. That from drillhole RN11577 was distinctive of the upper Loves Creek Member and indicated a uvio-lacustrine environment, whereas that from drillhole RN10692 was inconclusive.
Mafi c extrusives and intrusives
Basaltic intrusives and dolerite dykes occur at a few localities within the Bitter Springs Formation. At Curtin Springs in AYERS ROCK, extrusive porphyritic basalt, which is approximately 40 m thick, was encounted in BMR drillholes Ayers Rock 1 and 2. Geophysical modelling of the magnetic anomalies in this area indicates that the basalt dips at 45° to the south-southeast (Bladon and Davies 1982). The basalt from Ayers Rock 2 is medium-grained, contains numerous amygdales and has been altered to a chlorite-sericite rock. Clumps of chlorite are interpreted as having replaced olivine, whereas a ubiquitous light grey mottling could indicate altered devitrified glass. Abundant fine opaques include pyrite, magnetite, chalcopyrite and possibly ilmenite. Interpreted pillow structures are present and indicate subaqueous eruption.
5 Drillholes, depths and locations are: RN7001, 44.8-45.7 m (15 km to the east of Uluru); RN10692, 102-105 m (Dune Plains Bore eld); and RN11577, 147-150 m (immediately to the south of Uluru).
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A sample of basalt from Ayers Rock 2 has been dated using a Sm-Nd mineral isochron at 800 Ma (Zhao et al 1994).
Near Uluru, a dolerite intrusion within the Bitter Springs Formation was recognised from water drillhole RN10694. The hole was cored from 40-172 m and dolerite was encountered between 148-172 m. The dolerite is a strongly altered medium-grained rock with a recognisable typical doleritic texture. Adjacent calcareous rocks have been contact metamorphosed to chlorite marble and forsterite-sericite marble. Prior to these mafics being discovered in AYERS ROCK, the only other known interbedded basaltic volcanics in the Bitter Springs Formation were from an outcrop 100 km to the east-southeast of Alice Springs, and from oil exploration drillhole Ooraminna 1, which intersected an oligoclase-albite spilite (Wells et al 1970).
Inindia beds (LPin)
The Inindia beds are a thick unit of sandstone and lesser siltstone, chert and jasper that outcrops in Curtin. Ranford et al (1966) defined the unit and estimated its thickness to be 2130 m. It disconformably overlies the Bitter Springs Formation and is in turn overlain, probably unconformably, by the Winnall beds. Outcrop and drill hole data from the Amadeus Basin indicate a basinal thickening of the Inindia beds to the southwest in AYERS ROCK (Wells et al 1970). The unit is terminated abruptly against fault-controlled uplifted basement in the south.
Wells et al (1970) designated the reference areas for the Inindia beds to be the northern ridges around Mount Conner for the upper part, and an outcrop 20 km to the north of Curtin Springs for the lower part. At Mount Conner, sandstone with pronounced tabular crossbeds forms well defined concentric ridges that are 5-50 m in height. To the north, in the core of an anticline 20 km to the north of Curtin Springs, the lower beds outcrop as low ridges of sandstone, mudstone and chert that dip at a low angle and are partly covered by scree. Open folds on small- and large-scales exhibit north- to northeasterly-trending fold axes that may have been formed by the Petermann Orogeny (Young 1992). A variable veneer of calcrete obscures outcrop in places. Elsewhere on AYERS ROCK, drillhole cuttings of dark brown siltstone near Yulara are considered to be upper Inindia beds. During 1996, excavations at a locality some 2.5 km to the east of Uluru struck saprolitic material at shallow depth that may be weathered Inindia siltstone.
Wells et al (1964, 1970) correlated the Inindia beds with the Areyonga Formation in the northeast, and tentatively with the Carnegie Formation and Boord Formation in the west of the Amadeus Basin. The Inindia beds have since been divided into three informal units: a lower unit of possible tillite that is correlated with the Areyonga Formation, a middle unit that is correlated with the Aralka Formation and an upper unit that is correlated with the Pioneer Sandstone (Preiss et al 1978). Only the upper two of these outcrop in AYERS ROCK. In KULGERA, the three units have been recognised in Exoil drillhole Erldunda 1 and Pacific Oil and Gas drillhole Murphy 1 (Menpes 1991). Elsewhere in the Amadeus Basin, conglomerate beds of a similar age to the possible tillite horizon have been interpreted as recording a Late Proterozoic glacial event
(Wells et al 1967, 1970) that has been correlated with the Marinoan glaciation (Preiss et al 1978).
Dolostone from the top of the exposed section of lower Inindia beds, 20 km to the north of Curtin Springs, varies from massive to thinly bedded and laminated, and is white, or dark grey to green or red in colour. Chert, chert breccia and jasper are present. Sandstone beds at this locality contain interbeds of siltstone, chert, jasper and dolostone. Sharp lateral variations occur with beds lensing out over short distances.
A possible tillite bed at a location 6 km to the northeast of Mount Conner was reported to contain striated and faceted clasts and dropstones (Field 1991). It shows no obvious bedding and carries pebbles of chert, quartzite, siltstone and quartz that are rounded, up to 3 cm across, and in places broken. These are set within a light grey, poorly sorted, silty matrix. Angular quartz ranges from coarse sand to fine gravel. At Yulara, siltstone is the dominant lithology in water drillhole cuttings and there is also minor sandstone and dolostone. However, these are difficult to differentiate from dolostone of the underlying Bitter Springs Formation.
Wells et al (1970) considered the Inindia beds to have been initially deposited in shallow marine conditions, becoming deeper, but in the upper section the environment changed to a terrestrial braided fluvial setting. This change is reflected in a general absence of crossbedding in the middle unit, in contrast with the abundantly crossbedded upper unit, which forms the inner concentric ridge around Mount Conner.
Winnall beds (LPwi)
The Winnall beds are a sequence of sandstone and siltstone that were named by Ranford et al (1966) after Winnall Ridge in southern LAKE AMADEUS. They recognised four sub-units: a basal siltstone, followed by sandstone, siltstone, and sandstone. No complete section was found in the central part of Amadeus Basin, but the minimum thickness was determined to be 1524 m. Wells et al (1970) suggested a maximum exposed thickness of 2130 m. The lower siltstone (LPwi1) and sandstone (LPwi2) are exposed in the east of AYERS ROCK at Mount Conner, where the sandstone forms a resistant mesa that overlies siltstone. The lower sandstone is also exposed in the northwest, along with the upper sandstone (LPwi4) and these form prominent strike ridges in “The Sedimentaries”, a series of hills to the northwest of Yulara. The recessive upper siltstone (LPwi3) also occurs in the northwest but is poorly exposed. The Winnall beds appear to be thicker to the southwest in the Amadeus Basin and AYERS ROCK (Wells et al 1970), as are the underlying Inindia beds and are terminated abruptly against fault-controlled uplifted basement in the south.
The Winnall beds unconformably overlie the Inindia beds, but the contact is poorly exposed in AYERS ROCK. In the northeast, erosion has completely removed the formation and the Inindia beds are unconformably overlain by the Ordovician Stairway Sandstone, whereas in the northwest, the Winnall beds are unconformably overlain by the Mount Currie Conglomerate. Stewart (1993) considered open, west-trending folding of the Winnall beds at Mount Conner to be due to the Alice Springs Orogeny. In the west
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of AYERS ROCK, similar folds in the Winnall beds trend to the northwest. However, to the east of Kata Tjuta, some folds plunge shallowly to the northeast and may be due to the Petermann Orogeny.
The basal unit (LPwi1) is 150 m thick in the type area. It consists mainly of thinly bedded siltstone and fine, slightly calcareous silty sandstone. In AYERS ROCK, it outcrops adjacent to Mount Conner as low rounded hills with thin calcrete cover. Good exposures are found in creeks. The unit is generally micaceous and friable, and varies from dark brown when fresh to light brown on weathered surfaces. North of Mount Conner near the base of the unit, dolomitic and calcareous siltstone is exposed.
The second unit (LPwi2) is an orthoquartzite, which is 550 m thick at the Mount Conner type section. It is medium to coarse, poorly sorted and silicified. Thin sections reveal spherical quartz grains, many of which exhibit overgrowths, plus detrital tourmaline and zircon. The sandstone is dominantly thickly bedded but has some internal laminations. Several 1-2m thick interbeds of conglomerate occur immediately above the basal siltstone and these carry chert fragments. The sandstone has low-angle crossbeds, ripple marks, flute casts, and current streaming lineations. Sand casts that may represent synaeresis cracks are also present. These are typically 3-5 mm wide and 10-40 mm long and are generally straight, but in places are curved. The sand casts are pale in colour, in contrast with the light brown to red bedding surfaces, and are either slightly raised or depressed relative to the bedding surface. They crosscut and interconnect with one another, and are composed of smooth sand with no fine surface markings. They appear to be quite different to bioturbations in the overlying Stairway Sandstone.
The third unit (LPwi3) comprises thinly bedded, variegated siltstone and silty sandstone and is poorly exposed in AYERS ROCK. In the type area, it is 335 m thick. The uppermost unit (LPwi4) is a dark brown, poorly sorted, medium bedded sandstone. It forms strike ridges, ranges from silicified to friable, and contains weathered out clay pellets, chert fragments, small crossbeds, ripples and slumps. In the type area it is 180 m thick.
The Winnall beds and its correlatives occur widely within the Amadeus Basin. Wells et al (1964, 1966, 1970) correlated the unit with the Pertatataka Formation in the northern Amadeus Basin and with the Maurice Formation, Sir Fredrick Conglomerate and Ellis Sandstone in the west.
Wells et al (1970) considered the Winnall beds to be of shallow marine origin. They considered the unit to have been deposited in a subsiding depression with initial sedimentation commencing in an environment of restricted water circulation.
Mount Currie Conglomerate (–Cc)
The Mount Currie Conglomerate is exposed in northwestern AYERS ROCK, along the southwestern margin of the Amadeus Basin (Figures 13-15). Forman (1963) defined this unit of pebble, cobble, and boulder conglomerate, which unconformably overlies the Winnall beds at Mount Currie. Its age is probably latest Neoproterozoic or Cambrian, and this may correspond to the 560-530 Ma Petermann Orogeny (Scrimgeour et al 1999). Gillespie (1959) estimated a thickness of 1590 m but Forman (1963) estimated 6100 m, and this was supported by Sweet and Crick (1992). At Kata Tjuta, 650 m of Mount Currie Conglomerate is exposed. Cuttings from water drillholes confirm its presence beneath Cenozoic cover between major exposures and its subsurface extension eastward into the Dune Plains borefield adjacent to Yulara.
At Mount Currie, “The Sedimentaries” and to the west of Kata Tjuta, the Mount Currie Conglomerate unconformably overlies the Winnall beds. However, in the southern part of “The Sedimentaries”, beds are essentially parallel and an unconformity is not obvious. Wells et al (1970) correlated the Mount Currie Conglomerate with the Arumbera Sandstone elsewhere in the Amadeus Basin. The unit is also correlated with the Multitjulu Arkose (Sweet and Crick 1992). Forman (1963) recognised changes in clast types up-section from exclusively sandstone at the base, to porphyry-dominated followed by granite-dominated phenoclasts. This has been confirmed by current mapping. Three informal members (–Cca-c) are recognised.
Figure 13. Sandstone lenses in lower member of Mount Currie Conglomerate (FT570330)
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Basal member (–Cca)
A basal member with distinctive sandstone clasts is restricted to the northern margin of the Mount Currie-Kata Tjuta exposures at Mount Currie and “The Sedimentaries”. Outcrops form low ridges with densely packed cobbled surfaces.
Forman (1963) recognised the oligomictic nature of the basal unit and considered it to be thin. However, NTGS mapping at Mount Currie has indicated the existence of over two kilometres of outcrop normal to strike, and southerly dips of 15° near the base, which increase to 50° in outcrops further to the south. From these observations, a thickness of at least 1000 m is indicated.
The sandstone clasts are mostly 5-20 cm in diameter (cobbles to boulders), but can range up to 100 cm. They are typically very well rounded, many almost spherical, and are well packed. Sandstone clasts are thought to have
been derived from the Winnall beds, as they consist of densely packed, well rounded, medium to coarse quartz grains, which are well cemented with silica. Between the clasts is a medium-grained to granular white quartz sand; this also forms thin lenses and interbeds. A typical sample from an interbed (O94/87, FT579333) is a fine to coarse poorly sorted subarkose. This is composed dominantly of quartz, but has 15% clay, which has apparently been derived from the weathering of feldspar. Quartz grains are subangular to subrounded and range from 0.1-2 mm; some are of sheared metamorphic quartz. Disseminated opaques are present, together with traces of tourmaline. Rare lithic grains of possible rhyolite and phenoclasts of vein quartz and quartzite also occur.
Small rare chert and weathered tuff layers occur in the upper section of the member on the northern flank of Mount Currie. In the northern part of “The Sedimentaries”, the upper section is characterised by interbeds of medium- to coarse-grained and granular
Figure 14. Thick exposure of upper member of Mount Currie Conglomerate. Note boulder-sized clasts. Figure for scale (FT750010)
Figure 15 . Close up of polymictic conglomerate from upper member of Mount Currie Conglomerate, showing sub-rounded to rounded clasts of rhyolite, granite and basalt (FT750010)
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sandstone, feldspathic arenite, coarse chert conglomerate and thin red-brown haematitic siltstone. Chert clasts in the conglomerate were probably derived from the Inindia Beds. They are commonly angular, grey to black and banded. A typical sample of the chert conglomerate (O94/41B, FT731244) is poorly sorted, immature and contains clasts of banded chert, feldspar and altered basalt. The fine sandy groundmass contains microclasts and grains of 30% quartz, 10-15% feldspar (largely altered to clay), 10-15% chert and minor basalt (largely chloritised), and 40-50% of a very fine matrix. Quartz grains, some of which are rutilated, vary from elongate and angular to well rounded. Occasional pebbles to 6 mm in diameter are present. The feldspars are largely altered to clay, which is partially silicified. Chert grains are sub angular and have a dark banding, which is caused by opaques.
Middle member (–Ccb)
The middle member is a polymictic conglomerate with an igneous provenance. It overlies the basal member with a sharp contact that is obscured by soil cover. The member is dominated by phenoclasts of porphyritic rhyolite, and occurs around Mount Currie and west of Kata Tjuta, adjacent to the Docker River road. At Mount Currie, this member has a clast content of 70% porphyritic rhyolite, 20% basalt and 10% sandstone. However, variation does exist and on the northern flank of Mount Currie (O94/90, FT579319), the basalt content is 45%.
The basal member is not present to the northwest of Mount Currie or in the southern part of “The Sedimentaries”. In these localities, the middle member contains a high proportion of sandstone derived from the Winnall beds. Cobbles and boulders of sandstone are concentrated in particular lenses and beds and no other rock types are present as clasts. The typical composition of clasts from locality O94/125 (FT527328) is 55% sandstone, 35% porphyritic rhyolite and 10% basalt.
Phenoclasts in this member are poorly sorted. They range in size from pebbles to boulders (5-25 cm) and are subangular to well rounded. Phenoclasts are set in a dark, poorly sorted, medium to coarse lithic arenite, which also forms thin discontinuous lenses. These lenses have been more readily eroded than conglomerate layers and form indentations in otherwise rounded outcrops, so as to highlight the bedding. A typical sample of lithic arenite (O94/92, FT572314), from a lens on the northern flank of Mount Currie, contains microclasts and grains composed of 75% basalt, 7% quartz, 5% epidote and 2-3% rhyolite fragments, as well as traces of feldspar and chert, and 10% matrix. Basalt grains are altered and epidotized, but a quench texture is still visible. Quartz grains are angular and rhyolite grains are subangular to rounded.
Clast imbrications in outcrops at the microwave link tower (locality O94/57, FT598086) and to the west of Uluru-Kata Tjuta National Park indicate a northeasterly palaeocurrent direction, consistent with a source from the southwest. In the southern area, sand lenses are present and at locality O94/77 (FT675049), a felsic-mafic mineral segregation layering is developed in a sandstone interbed.
Upper member (–Ccc)
The upper member has more granite than rhyolite phenoclasts. The proportion of granite phenoclasts increases up-section from 30% to 50%, and defines a transitional boundary with the middle unit. A typical clast mix is 60-80% granite, 20-40% basalt, minor porphyritic rhyolite, and rare sandstone and granitic gneiss. As in the middle member, imbricated clasts are indicative of northeast palaeocurrent directions. Phenoclasts are tightly packed and are set in a dark intergranular sand matrix, which also forms thin discontinuous lenses between conglomerate layers. These lenses are similar to those at Mount Currie, in that they are preferentially eroded and have beds that dip to the southwest at 15°.
Mutitjulu Arkose (–Cm)
The Mutitjulu Arkose (new name, see Appendix 1) was previously informally named the “Uluru arkose”. It is considered to be latest Neoproterozoic to Cambrian in age
Figure 16. Near-vertical beds of Mutitjulu Arkose at Uluru, showing differential erosion and distinctive corrugated outcrop silhouette
because of its syn-orogenic nature (Forman 1966, Sweet and Crick 1992, Scrimgeour et al 1999). The main exposure of this unit rises abruptly from the surrounding plain at Uluru and forms an isolated but famous inselberg, approximately 3 km by 2 km in plan and 300 m high (Figure 3). Strata dip steeply to the southwest at 85°and reach at least 2400 m in thickness.
2020
Cuttings from water drillholes indicate that the subsurface extent is restricted to the vicinity of Uluru itself, which is a massive outcrop largely free of jointing. Differential erosion of the steeply dipping beds has resulted in the distinctive corrugated outcrop silhouette (Figure 16). Forman (1965) and Sweet and Crick (1992) considered the arkose to be a lateral variant of the Mount Currie Conglomerate. It may also be equivalent to the Arumbera Sandstone in the northern Amadeus Basin.
The Multitjulu Arkose is classified as an arkosic arenite, using the scheme of Pettijohn et al (1973). IP Sweet (pers comm 1994) reported an average composition of 50% feldspar, 25-35% quartz and up to 25% rock fragments. The freshest material at Uluru is found under overhangs and is grey in colour, with pink or green tinges. Sweet (pers comm 1994) recognised four rock facies, based on lithology, grain size and sedimentary structures. These are:
• well sorted, planar bedded or ripple laminated, very fine to medium sandstone;
• trough crossbedded sandstone to granule conglomerate;• planar bedded and crossbedded granule to pebble
conglomerate; and• massive conglomerate.
The trough crossbedded sandstone to granule conglomerate facies is the most common (Figure 17). Sweet (pers comm 1994) reported that the finer arkosic beds are well sorted and generally darker in colour, and this reflects a higher content of opaque minerals. Coarser arkosic beds are poorly sorted and grade into pebble conglomerate (pebbles up to 40 mm). Grain sizes within the Mutitjulu Arkose appear to coarsen to the southwest.
In thin section, K-feldspar and quartz are dominant (Figure 18). Minor plagioclase, opaques, microclasts of basalt and rare grains of probable rhyolite, orthopyroxene and sphene also occur. Clasts and grains generally range from 2-4 mm and are set within a matrix of polycrystalline quartz. Grains are angular to subangular and are closely packed. K-feldspar occurs as angular to subangular perthitic grains. Quartz is
angular and only lightly dusted with inclusions. Rare spherical grains are interpreted to be quartz amygdales from basalt. Plagioclase occurs both as individual subrounded grains and as highly altered inclusions within K-feldspar. Basalt clasts are subrounded and have a quenched texture. They are invariably replaced to some degree by chlorite and epidote.
Sedimentary features include multidirectional crossbedding, scour and fill troughs and ripples. These indicate a high-energy fluvial environment of broad shallow channels or sheet floods. Sweet (pers comm 1994) interpreted the four-fold facies as reflecting progressively higher energy of transport. The highest energy massive conglomerate facies may have resulted from debris flows.
Stairway Sandstone (Os)
This unit is Ordovician in age and is widespread under the greater part of the Amadeus Basin, although it has only limited exposure. A thickness of 600 m has been measured in the north, but this decreases to the south. Prichard and Quinlan (1962) originally defined the Stairway Greywacke from the northern Amadeus Basin in HERMANNSBURG. Wells et al (1965) amended the name to Stairway Sandstone. Along with the overlying Stokes Siltstone and Carmichael Sandstone, this unit is part of the Larapinta Group.
On AYERS ROCK, the Stairway Sandstone is confined to the northeast, where Young (1992) estimated a thickness of 70-100 m. It outcrops in rubble-covered strike ridges that are up to 40 m high. Outcrops are commonly silicified. Cook (1966) divided the sequence in the northern Amadeus Basin into lower, middle and upper units on the basis of lithology. Only the upper unit is exposed in the south of the basin, which occurs in AYERS ROCK.
The Stairway Sandstone contains interbeds of red sandstone, dolostone and siltstone. It unconformably overlies the Inindia beds 20 km to the north of Curtin Springs. Young (1992) described the unit in AYERS ROCK as a white to grey, medium to coarse quartz sandstone that contains interbeds of fine kaolinitic sandstone and siltstone. The sandstone is very coarse in places, and has
Figure 17. Trough crossbeds in Mutitjulu Arkose (width of view approximately 4 m)
21
occasional small pebbles and thin pebble conglomerate layers. Bedding planes frequently display bioturbation in the form of burrows, tracks and trails.
Prichard and Quinlan (1962) and Wells et al (1966, 1970) noted that trace fossils are abundant in the Stairway Sandstone. They include Diplocraterion (vertical U-shaped burrows) and Cruziana. Wells et al (1970) noted the presence of grey phosphate pellets, up to 2.5 cm diameter, from a 30 cm thick coarse sandstone bed, located 19 km to the northeast of Curtin Springs. Wells et al (1966) reported pseudomorphs after halite at Mount Ebenezer on KULGERA. Wells et al (1970) suggested that the unit was deposited in a wide low-energy epicontinental sea that was bordered by a narrow high-energy environment on the northern side. They further noted that the presence of phosphate indicates slow rates of sedimentation, as would be consistent with a lagoonal environment.
Stokes Siltstone (Ot)
This unit was formerly part of the “Stokes Formation” as originally de ned by Prichard and Quinlan (1962). The “Stokes Formation” was subsequently divided and rede ned by Wells et al (1970), who named the lower, siltstone-dominated section the Stokes Siltstone and the upper part, the Carmichael Sandstone. Like the Stairway Sandstone, this unit is thick in the northern Amadeus Basin (650 m), but thins signi cantly in the south to an estimated 100 m in CURTIN. In AYERS ROCK, it is a poorly exposed recessive unit that forms a valley and low hills between ridges of Stairway Sandstone and Carmichael Sandstone. It is interpreted as being conformable with both of these units. Wells et al (1970) reported that in the western Amadeus Basin, the Stokes Siltstone unconformably overlies the Bitter Springs Formation, whereas elsewhere, it is conformable on the Stairway Sandstone. It is unconformably overlain by the Mereenie Sandstone in the east of the Amadeus Basin.
The Stokes Siltstone comprises siltstone and mudstone, and minor limestone and sandstone. Pink and grey-green limestone is more common in the lower part (Wells et al 1970). The limestone is moderately resistant to erosion
and is generally composed of fossil fragments that include brachiopods, trilobites, gastropods, pelecypods, echinoderms, nautiloids, conodonts and some trace fossils. Pseudomorphs after halite are also present. In CURTIN, Young (1992) reported minor ne kaolinitic sandstone and minor thin interbedded dolomitic siltstone and dolostone. Wells et al (1970) proposed that the depositional setting was a shallow epicontinental sea with restricted circulation that covered the area of the present Amadeus Basin.
Carmichael Sandstone (Oc)
This unit comprises red-brown, yellow, purple-brown and pale brown sandstone, which is kaolonitic and feldspathic in part and thinly to medium bedded. The sandstone is ne to medium and moderately to poorly sorted, and is interbedded with red-brown or green siltstone, which is micaceous in places. Wells et al (1970) named and de ned the Carmichael Sandstone which, along with the Stokes Siltstone, had previously been de ned as part of the “Stokes Formation” (Prichard and Quinlan 1962). The type section is located in George Gill Range, 100 km to the north of Curtin Springs. In common with the underlying Ordovician sediments, the unit is relatively widespread beneath the Amadeus Basin, but is poorly exposed. However, in contrast with these units, it thickens signi cantly from less than 30 m in the north to more than 150 m in the south (Wells et al 1970). In AYERS ROCK, it is con ned to the northeast where it outcrops as sinuous ridges. Young (1992) reported a thickness of 120-200 m, as determined from aerial photographs. The Carmichael Sandstone in AYERS ROCK conformably overlies the Stokes Siltstone and is unconformably overlain by Cenozoic sediments. Elsewhere in the Amadeus Basin, it is unconformably overlain by the Mereenie Sandstone (Wells et al 1970).
Wells et al (1970) noted that the Carmichael Sandstone is coarser in the southern part of the Amadeus Basin and contains pebbles that include minor chert. Crossbedding and ripple marks are common and there are occasional halite pseudomorphs. They also reported the presence of Cruziana and other trace fossils and proposed that the unit was deposited in an estuary or delta that had periods of high salinity.
Figure 18. Photomicrograph of Mutitjulu Arkose, showing coarse, angular feldspar-rich grains (width of view approximately 10 mm)
22
Horseshoe Bend Shale (Dh)
The Devonian Horseshoe Bend Shale is part of the Finke Group (Wells et al 1966, 1970) and is con ned to the eastern end of the Amadeus Basin. In AYERS ROCK, it outcrops in a few places to the northeast of Curtin Springs, but is poorly exposed and is masked by calcrete and playa lake sediments. The formation contains interbedded micaceous shale and siltstone, and rare ne sandstone. Its colour varies from red-brown to light green or off-white. Wells et al (1966) reported abundant biotite in the shale, the presence of gypsum, pseudomorphs after halite, ripple marks and mud cracks. The unit was deposited in a uviatile or estuarine environment and the presence of mica indicates a contribution from granitic basement.
Wells et al (1966) estimated a thickness of 91 m at the type locality. Wakelin-King (1990) reported a thickness of 215 m from the NTGS stratigraphic drillhole K3, which is located in the far west of KULGERA. In this drillhole, it is underlain, apparently conformably, by the Langra Formation. Paci c Oil and Gas drillhole Murphy 1 in KULGERA intersected 566 m of the unit (Menpes 1991). Further east in FINKE, the Horseshoe Bend Shale overlies the Langra Formation and is unconformably overlain by the Idacowra Sandstone (Wells et al 1970).
MESOZOIC AND CENOZOIC SEDIMENTS
MESOZOIC SEDIMENTS
Sediments of this age are not exposed on AYERS ROCK, but they are known from drillholes in the vicinity of Uluru. The nearest recognised outcrop of Mesozoic age is approximately 200 km to the east of Uluru, in KULGERA (Edgoose et al 1993). Two water drillholes (RN10598 and RN11577) reveal coarse, moderately well sorted quartzose sandstone with interbedded lignitic sandstone and siltstone. Palyno oras from the lignite are Upper Cretaceous (Macphial 1997). The Mesozoic sediments are overlain by an undivided sequence of Palaeogene-Neogene sand and clay.
CENOZOIC SEDIMENTS
In AYERS ROCK, Palaeogene-Neogene sediments occur as thin sheets of limited areal extent and as thick units in palaeo-drainage valleys (Figure 19). They are overlain by an extensive thin Quaternary cover.
Non-exposed Cenozoic sediments
Non-exposed sediments occur in palaeovalleys etched out along structural corridors. Palaeogene-Neogene sediments form an important aquifer in AYERS ROCK and drilling has intersected up to 100 m of sediment. These overlie both older basement rocks and Amadeus Basin sedimentary rocks.
Jacobson et al (1988, 1989) delineated the thickness of Cenozoic strata from available drillhole data. The accumulations re ect a depression that stretches over 500 km from Lake Hopkins in Western Australia to Erldunda on the Stuart Highway in the east. This depression de nes an old regional drainage system that owed from west to east. Playa lakes now de ne the modern internal drainage system, which
is known as the central Australian groundwater discharge zone.
In the Dune Plain bore eld area immediately to the west of Yulara, up to 100 m of sediments were deposited in a palaeodrainage valley etched along a northeasterly structure (English 1998). The orientation of Inkanunna Creek in southwestern AYERS ROCK lies parallel to this trend. Another palaeovalley with signi cant sediment accumulation occurs beneath the northerly owing Britten Jones Creek within granitic basement (Jacobson et al 1988).
Logs and cuttings from Dune Plains bore eld drillholes reveal that dolostone and evaporites of the Bitter Springs Formation form the pre-Cenozoic basement. Depth to the paleaovalley oor is variable even within short distances. Cuttings from drillholes include sand, clay, gravel and laterite (English 1998). Laterite occurs in the northern half of the bore eld at a depth of 33-35 m. The laterite is generally 5-6 m thick, but in some holes it reaches 22 m (Knott 1981). Clay beneath laterite is generally white, whereas that above the laterite is brown. This laterite layer may represent an old Palaeogene-Neogene peneplain surface, which has been largely eroded in the south.
Sandstone (Czs)
This unit is known from one location (FS938757), which is 20 km to the south-southwest of Uluru. It outcrops as a thin rubbly at sheet that is unconformable on granitic basement. The sandstone is composed of ne, closely packed quartz grains, minor intergranular muscovite and minor ne sericite, which may be set in a matrix (up to 50%) of weathered and ferruginized muscovite and sericite. Chert grains to 1% are present and accessory minerals include opaques, detrital tourmaline and zircon. The ne quartz is rounded to angular, but a few medium to coarse grains are angular. Many grains have silica overgrowths.
Talus and scree (Czt)
This unit consists of dissected talus fans that are found along the anks of ranges as wedge-shaped deposits (as at Mount Conner). It also occurs around the base of the ranges as low rounded rises and hills. The fans reach an estimated thickness of 30 m and consist of poorly sorted pebbles and boulders of local derivation that are set in a sandy, clayey matrix. At Mount Currie, scree that consists of reworked Mount Currie Conglomerate occurs along the northern ank of the range. Recent erosion has removed nes from the surface layer, so as to leave a surface veneer of loose clasts.
Skeletal residual soil (Cz)
These are present in the southern half of AYERS ROCK, and are limited to areas proximal to Musgrave basement rocks. The soils are generally thin and consist of coarse sand to pebbles of the underlying rocks in a variable sandy or clayey matrix.
Ferricrete (Czf)
Laterite is developed over some basement units and is exposed in a few places in southern AYERS ROCK.
23
QUATERNARY SEDIMENTS
Calcrete (Qc)
Calcrete is a secondary cryptocrystalline form of low-Mg calcite that has varying proportions of detrital quartz, feldspar and clay minerals (Milnes and Hutton 1983). It is extensively
developed in northern AYERS ROCK, where it overlies sediments of the Amadeus Basin, but is commonly obscured by aeolian sand. The calcrete is mainly white and occasionally grey or pink. On aerial photographs, it shows as pale white areas commonly riddled by rabbit burrows. In playas north of Curtin Springs, calcrete forms duricrust caps on low scarps above the Horseshoe Bend Shale. Evidence from drillholes
Figure 19. Isopach map showing thickness of Cenozoic deposits in AYERS ROCK and southern LAKE AMADEUS (after Jacobson et al 1988)
Uluru
Kata Tjuta
Mt Connor
Yulara
Lake Amadeus
o o o o
o
o
o
100
8060
4020
20
100
20
20
80
60
4020
80
80100
40
40
20
20
40
20
20
20
20
20
20
20
2040
40
20
20
20
80 Thickness of Cainozoic deposits (m)
Less than 20mGreater than 100m 80-100m 60-80m 40-60m 20-40m
30 km0
130 30’ 131 00’ 131 30’ 132 00’24 30’
25 00’
25 30’
26 00’o
SpringsCurtin
24
on Curtin Springs station indicates that the calcrete may be over 10 m thick. Veins of chalcedony (opaline silica) up to 10 cm thick are present in the calcrete.
Jacobson et al (1988) and Arakel (1991) gave detailed descriptions of two calcrete types. Phreatic calcrete, which is commonly associated with chalcedony, was dated at 75 000-34 000 ybp (years before present) by electron spin resonance (Jacobson et al 1988). Younger, higher level and more widespread vadose calcrete was dated at 27 000-22 000 ybp (Jacobson et al 1988) and overprints phreatic calcrete in places. Recent Carbon-14 dating of calcrete from “The Sedimentaries”, to the northeast of Yulara, yielded 6390 ± 80 ybp and 12 070 ± 100 ybp (G Jacobson pers comm 1996) and this indicates more recent periods of calcrete formation.
Calcretes are reliable shallow aquifers in areas overlying the Amadeus Basin in northern AYERS ROCK. Groundwater resources that are associated with calcretes are found near to Lake Amadeus and playa lakes where the water table is at a depth of 4-6 m (Jacobson et al 1988, 1989).
Talus (Qt)
This younger talus unit forms thin deposits (generally less than 10 m thick) on the anking slopes and bases of large ridges. Unlike older talus deposits, these are not dissected by modern drainage systems. The talus consists of unconsolidated, poorly sorted and generally sub-angular particles ranging in size from sand to boulders. The lithology
of the source ridge determines the composition of the talus deposits. At Mount Conner, talus boulders of Winnall Sandstone are up to 5 m in diameter. Talus deposits are commonly too small to show at map scale and the underlying basement lithology is usually depicted.
Playa sediments (Qp)
Playa lakes along the northern boundary of AYERS ROCK form part of the Lake Amadeus chain, which is regionally located in an east-west depression from Lake Hopkins in Western Australia to Erldunda in the east (Figure 20). These playa lakes are part of the modern internal drainage system known as the central Australian groundwater discharge zone (Jacobson et al 1989). Playa lake sediments consist of reddish-brown lacustrine clay and sand, and gypsiferous layers. They are generally less than one metre thick and are similar to those investigated by NTGS in KULGERA (Wakelin-King 1989). However, some playa lakes contain sediments that are more than 10 m thick.
The central areas of playa lakes are at and are overlain by a thin halite crust that relates to ood surfaces. These appear as distinct white areas on aerial photographs. The underlying mud carries a range of evaporite salts including sulfates and chlorides of calcium, magnesium and potassium. Of these, gypsum is the most common and forms crystals up to 5 mm. The playas host a variety of evaporite minerals, including zeolites at Spring Lake, which is located to the northeast of Curtin Springs (Arakel
Figure 20. Regional extent of playa lake system and major drainage channels; box shows location of AYERS ROCK (after Chen et al 1994)
25
1987). A narrow fringing beach of gypsum sand (kopi) de nes the playa margin. In places, there may be bordering gypsum dunes that have anking gypcrete crusts, beyond which is red dune sand.
An investigative program on evaporative playa minerals at Spring Lake commenced in 1984 (Jacobson et al 1989). A drilling program was followed by groundwater observations and levelling, petrographic studies of drillcore (Arakel 1987) and dating of core and surface samples. Drilling intersected a dolomite layer containing 35% zeolites at a depth of 9.5 m. The zeolite species analcime and chabazite were most common, and minor phillipsite and mordenite were also present. The dolomite was considered to be unrelated to the modern hydrological regime (Arakel and Wakelin-King 1991). Dating of playa deposits from Spring Lake by electron spin resonance yielded 16 000-8000 ybp for the gypsite and gypcrete deposits (Jacobson et al 1988). The playa system may have economic potential for evaporite minerals.
Gypsiferous deposits (Qpg)
Gypsiferous sand is associated with playa lakes in the far north and northeast of AYERS ROCK. Gypsum occurs in areas marginal to the playas as friable gypsiferous sands (Qpg) which may be overlain by a resistant gypcrete cap. Gypsiferous sand (kopi) is a white, powdery mass of ne crystals. The sands range from white to pale brown and red-brown where they are mixed with clay, red sand and calcrete fragments. They are a paler colour on aerial photographs than red aeolian sand (Qs). Gypsum crystals that occur individually or in aggregates on lake surfaces are mapped as playa sediments (Qp). Other gypsum deposits include mounds adjacent to playas or islands within them.
Further descriptions of gypsiferous deposits and playa lakes are presented in Jacobson et al (1988), Wakelin-King (1989), Arakel (1991), Edgoose et al (1993), Chen et al (1991) and Chen (1994).
Colluvium (Qr)
Deposits of colluvium or sheet ow form distinctive areas of red soils that are characterized on aerial photographs by swirling, arcuate patterns of thick scrub6 on bare areas (Wakelin-King 1999). Colluvium is common in broad plains near rock outcrops and in depressions between sand dunes. More vegetation is developed in areas of Qr than in sand plains (Qs), although local re burns may affect this. The colluvium is reddish-brown and sand-dominated but varies from mud to gravel. A higher response in the potassium channel of airborne radiometrics occurs over Qr interdunal areas due to clay fractions that are higher than in sand dunes. Near areas of outcrop, there is a higher proportion of coarse sand and gravel.
Aeolian sand (Qs)
Sand plains and dunes elds cover over half of AYERS ROCK. This aeolian sand is distinctly red in colour and generally of subangular, ne to medium quartz. The colour is the result
of microscopic particules of clay and iron oxide adhering to the grain surface (Norris 1969, Mabbutt 1977) and these are “ xed” with a minute amount of secondary silica. The sand also contains minor black magnetite. A higher response in the thorium and uranium channels of airborne radiometrics over the dunes probably indicates that traces of thorium- and uranium-bearing heavy minerals are higher in dunes than in colluvial units. Mabbutt (1968) suggested that the sands of the plains are derived from crystalline rocks, whereas the sands of dunes are derived mainly from sedimentary rocks. Dunes are well developed in the north and east of AYERS ROCK, where they overlie Amadeus Basin sedimentary rocks. Sand plains are proli c in the southwest, where they closely match the area of crystalline basement.
The dunes form part of the central Australian anticlockwise dunefield whorl (Brookfield 1970, Bowler 1976). On AYERS ROCK, dunes are irregular and discontinuous and are classi ed as the reticulate type, which Mabbut (1968) related to more variable winds near the anticyclonic centre. However, some longitudinal dunes of several kilometres length do exist. Reticulate dunes form a network of ridges that enclose depressions, the network being indicative of two or three wind directions. The dunes exhibit an overall southeasterly trend and may attain a height of 15 m. At some localities, dunes cover low rock outcrops. In areas adjacent to elevated outcrops, they form climbing dunes or echo dunes (Mabbutt 1977, 1984). Small shrubs have stabilized most dunes, whereas the sand plains are populated by a variety of shrubs, small trees and spinifex. White calcrete occurs at the base of some dunes, particularly the eroded ones. The sand dunes probably resulted from a period of alluviation in the Pleistocene. Studies in the Lake Eyre basin in South Australia indicated that dunes there were formed between 40 000-20 000 ybp (Callen and Nanson 1992). The period of maximum aridity and dune building was between 20 000-16 000 ybp (Jacobson et al 1988) and this correlates with the last glacial maximum (Chen et al 1991).
Alluvium (Qa)
Stream-deposited sediments are not common and are generally restricted to areas of ranges and hills that have a high surface runoff after rain. Immediately adjacent to their source areas, deposits are dominated by cobbles, pebbles and gravel that grade downslope to sand. In ow, these are relatively high energy streams and most of the silt-clay has been winnowed and dispersed as overbank, outwash or sheet ood deposits at the point where the streams braid-out and disappear into at lying sand plains.
STRUCTURE AND METAMORPHISM
A full account on the structure and metamorphism of AYERS ROCK will be presented in a forthcoming NTGS report on the Musgrave Block (Edgoose et al 2002). Only a brief synopsis of the topic is presented here. Previous studies on the northern Musgrave Block include Edgoose et al (1993), Camacho et al (1995), Camacho (1997), Scrimgeour et al (1999) and Camacho and McDougall (2000).
6 Typically mulga: Acacia aneura.
26
Musgravian Event
The Mulga Park and Fregon subdomains have similar metamorphic and structural histories (Camacho and Fanning 1995). Granitic gneiss of both subdomains was metamorphosed and deformed by the 1200 Ma Musgravian Event, which produced a strong compositional layering, as well as partial melting. The Musgravian Event took place prior to, or contemporaneous with granite emplacement at 1190-1140 Ma. It is possible that the Opparinna Metamorphics in the Mulga Park subdomain are older than 1200 Ma and were also affected by the Musgravian Event.
Petermann Orogeny
The 560-530 Ma Petermann Orogeny is the dominant deformational event in AYERS ROCK. Numerous studies on the Petermann Orogeny include Edgoose et al (1993), Camacho and Fanning (1995), Clarke et al (1995), Glikson and Clarke (in Glikson et al 1996), Camacho (1997), Scrimgeour et al (1999), Scrimgeour and Close (1999) and Camacho and McDougall (2000). The Petermann Orogeny formed a pervasive mylonitic foliation and overprinted prior fabrics. Multiple thrust zones structurally repeated granite, Dean Quartzite and Pinyinna beds. Some thrusts strike to the northeast in southwestern AYERS ROCK and dominate the magnetic image (see map face). Many of the mineral lineations recognised in this area plunge to the northeast. Another series of thrusts strike approximately east-west on ALLANAH and are parallel to the main trend of quartzite ridges.
Late in the Petermann Orogeny, lower crustal granulite facies gneiss of the Fregon subdomain and mid-crustal amphibolite facies rocks of the Mulga Park subdomain were juxtaposed by low angle thrusts that carried granulite from the south over the amphibolite, as described by Bell (1978), Maboko et al (1992), Edgoose et al (1993), Camacho and Fanning (1995) and Scrimgeour et al (1999). The south-dipping thrusts include the Woodroffe Thrust (Major et al 1967, Collerson et al 1972, Forman and Shaw 1973, Camacho et al 1995, Scrimgeour et al 1999, Camacho and McDougall 2000), plus thrusts on AYERS ROCK. Coarse, syn-orogenic uvial sediments that were deposited during the Petermann Orogeny include the Mount Currie Conglomerate and Mutitjulu Arkose (Forman 1965, Wells et al 1970, Sweet and Crick 1992). These sediments were probably deposited in a piedmont setting at the base of the emerging Petermann Ranges.
Deformation associated with the Petermann Orogeny also affected the Amadeus Basin. Stewart (1993) attributed some folds in the southern Amadeus Basin to the orogeny. Possible examples in AYERS ROCK include open folds with north- to northeast-trending axes in the Inindia beds, 20 km to the north of Curtin Springs (Young 1992) and broad open folding of Winnall beds sandstone about a north-trending axis, to the west of Kata Tjuta. The Mutitjulu Arkose and Mount Currie Conglomerate may have also been folded in the late Petermann Orogeny. Read (1978) reported Pinyinna beds juxtaposed over Mount Currie Conglomerate to the east of Kata Tjuta, and this was perhaps due to thrusting in a late
stage of the Petermann Orogeny. In addition, folds within the Winnall and Inindia beds in the Murphys and Erldunda Ranges in KULGERA must have been produced by the Petermann Orogeny prior to these rocks being onlapped by Ordovician sediments (Edgoose et al 1993).
Alice Springs Orogeny
During late Devonian and Carboniferous times, Proterozoic and Palaeozoic rocks of the Amadeus Basin were folded into east-trending, shallow-plunging folds (Shaw et al 1992, Collins and Shaw 1995). The non-cylindrical nature of the folds is indicated by sinuous outcrop patterns and dome-and-basin structures in northeastern AYERS ROCK.
GEOCHEMISTRY
GRANITIC ROCKS
The geochemistry of a total of 44 analysed granitic and rhyolitic samples is presented in Appendix 2. Analysed samples include: the Allanah Gneiss and granulite facies granitic gneiss (1550 Ma); the extensive Kulpitjata Granite Complex (1150 Ma); and younger granite and rhyolite, including the Nulchara Charnockite, Michell Nob Granite and rhyolite clasts from the Mount Currie Conglomerate (1050 Ma).
1550 Ma granitic gneiss
Four samples of 1550 Ma granitic gneiss were analysed (Appendix 2a); these include two samples of amphibolite facies Allanah Granitic Gneiss and two samples of granulite facies granitic gneiss. The few samples analysed are of metaluminous granite7, although peraluminous gneiss may be more common in nearby South Australian outcrops (Camacho 1997). On a total alkali versus silica plot, they are subalkalic. Camacho and Fanning (1995) rst pointed out the close age and compositional similarities between granitic gneiss from amphibolite and granulite facies terrains in this area.
1150 Ma granitic rocks
Thirty-four samples of the Kulpitjata Granite Complex were analysed and have a spread of SiO2 from 64.3-75.2 wt% (Appendix 2b, Figure 21). Incompatible elements are somewhat variable (eg K2O: 3.3-6.9 wt%), as are rare earth elements (some are HREE-enriched and some are HREE-depleted). The granites are largely metaluminous except where sheared rocks have been altered to more peraluminous compositions by the conversion of feldspars to quartz plus mica. The Kulpitjata Granite Complex shows an increase in the LREE/HREE ratio (and LREE enrichment) with increasing silica.
1050 Ma granitic rocks
Two samples of the Nulchara Charnockite and two of the Michell Nob Granite were analysed, as were three samples
7 Alumina saturation index (molecular Al2O3/K2O+Na2O+CaO) >1.
27
a
b
c
d
e
f
g
Figure 21. Selected Harker variation diagrams for granitic rocks, showing variations for (a) K2O, (b) MgO, (c) Ni, (d) Rb, (e) Sr, (f) TiO2 and (g) Y; triangles - Kulpitjata Granite Complex; asterisks - Nulchara Charnockite; crosses - felsic granulite gneiss; circles - Allanah Gneiss; diamonds - Michell Nob Granite, plus symbols (+) - rhyolite clasts in Mount Currie Conglomerate
of rhyolite clasts from the Mount Currie Conglomerate (Appendix 2a). On an ASI plot, they are all metaluminous. However, in terms of total alkalis versus silica, they mostly plot as subalkalic. Felsic clasts from the Mount Currie Conglomerate have depleted Sr, undepleted Y and high HREE, and this is consistent with crustal melting at moderate pressures where garnet is not stable (Tarney et al 1987).
28
MAFIC ROCKS
A total of 7 mafic rocks were analysed (Appendix 2c). These included four dolerite dykes, two gabbros and one basalt clast from the Mount Currie Conglomerate. The samples probably represent three different magma types and indicate the diversity of ma c magmatism in the northern Musgrave Block. Two dolerite dyke samples (BJ96/277B and A93/43) contain olivine and clinopyroxene, and have low silica compositions that closely match those of the Alcurra Dyke Swarm (formerly named the Kulgera dykes; Camacho et al 1991, Zhao and McCulloch 1993, Edgoose et al 1993, Camacho 1997). Four samples (dolerite dykes A93/214 and A93/205, a basalt clast from the Mount Currie Conglomerate O96/75, and gabbro A93/121) have elevated silica, potash and incompatible elements including Zr, P, Ti, La and Ba. Their geochemistry matches published analyses of the Mummawarrawarra Basalt of the Tollu Group, which is dated at 1078 ± 5 Ma (Glikson et al 1996, Sheraton and Sun 1997). The third group is represented by a two-pyroxene gabbro (MP61) that was collected from northeastern WOODROFFE in northern South Australia. It was considered to be part of the 1080 Ma Mount Woodroffe norite group by Camacho (1997).
QUARTZITE
Twenty samples of Dean Quartzite and metamorphic basement quartzites were analysed for rare earth elements (REE). Some quartzites from AYERS ROCK and KULGERA were found to have elevated REE contents (Appendix 2d).
GEOCHRONOLOGY
A summary of new NTGS geochronological data for AYERS ROCK is presented in Table 3. Previous geochronological studies on samples from AYERS ROCK were reported by Camacho (1990, 1997) and Camacho and Fanning (1995). Edgoose et al (1993) and Scrimgeour et al (1999) provided
summaries of isotopic dating in the adjacent NT map sheets KULGERA AND PETERMANN RANGES, respectively.
U-PB ZIRCON GEOCHRONOLOGY
1600 Ma zircons in Opparinna Metamorphics
Ion-microprobe analyses of zircons from quartzite in the southern Kelly Hills, to the west of Mulga Park Station, reveal a single age population of 1603 ± 36 Ma. This date indicates that the zircons were derived from older granites and is a maximum age for deposition. There are no 1150 Ma-aged zircons, but a pre-1150 Ma age for the Opparinna Metamorphics is indicated by the intrusion of dykes of the Kulpitjata Granite Complex at this location.
1550 Ma granitic gneiss
A major phase of granite emplacement took place at 1550 Ma, as is indicated by four samples of granitic gneiss dated by the SHRIMP U-Pb zircon method. A sample of Allanah Gneiss (A94/13788) from southwestern AYERS ROCK contains magmatic zircon rims on inherited cores; these have yielded an interpreted igneous crystallisation age of 1591 ± 30 Ma (reconnaissance data) and an inherited core age of about 1700 Ma. To the east, zircons from a similar sample (A93/63) lack discernible rims or inherited cores and have been dated at 1539 ± 23 Ma. Zircons from an amphibolite facies granitic gneiss (MP43) from MULGA PARK have been dated at 1554 ± 23 Ma (Camacho and Fanning 1995) and this date was interpreted as the age of igneous crystallisation. One zircon from this population has a 2000 Ma core as well as 1206 ± 23 Ma metamorphic overgrowths, interpreted as re ecting the Musgravian Event. Another sample of this gneissic unit (MP98), also from southeastern AYERS ROCK, has 1563 ± 15 Ma rims on cores of unknown age (Camacho 1997). Camacho carried out U-Pb monazite work on this sample and obtained a metamorphic age of 1177 ± 6 Ma.
Table 3 Summary of new NTGS U-Pb geochronological data for AYERS ROCK. SHRIMP refers to SHRIMP U-Pb zircon method (analyses by CM Fanning, PRISE); Kober refers to the Kober Pb-Pb zircon evaporation method (analyses by J Foden, University of Adelaide)
8 Later resampled for geochemical analysis as A97/1378.
Sample AMG grid ref (GDA94) Easting Northing
Rock unit Date Method
A94/1378 659853 7151386 Allanah Gneiss 1591 ± 30 Ma Reconnaissance data SHRIMP A93/63 679433 7138216 Allanah Gneiss 1539 ± 23 Ma Reconnaissance data SHRIMP BJ96/280 740783 7156366 Hornblende-pyroxene granulite gneiss 1563 ± 22 Ma SHRIMPA92/10A 689162 7138696 Kulpitjata Granite Complex 1150 ± 19 Ma SHRIMPA94/644 674974 7153616 Kulpitjata Granite Complex 1552 ± 40 Ma (inherited cores),
1191 ± 55 Ma (igneous) Reconnaissance data SHRIMP
A94/1402 657803 7152636 Kulpitjata Granite Complex 1197 ± 21 Ma SHRIMPBJ96/220 743333 7140656 Kulpitjata Granite Complex 1181 ± 34 Ma Reconnaissance data SHRIMP BJ96/277A 737633 7161666 Kulpitjata Granite Complex 1182 ± 27 Ma SHRIMPBJ75 741673 7128826 quartzite from Oparinna
Metamorphics 1603 ± 36 Ma Reconnaissance data SHRIMP
MP94/503 763503 7137076 Katiti Granite (Kulpitjata Granite Complex)
1172 ± 4 Ma Kober
O94/57F 659883 7208615 Rhyolite clast from Mount Currie Conglomerate
1062 ± 6 Ma Kober
29
Sample BJ96/280 from northern BRITTEN JONES is of hornblende-garnet-pyroxene granitic gneiss, which has reached granulite facies. Zircons from this sample have cores dated at 1563 ± 22 Ma.
1150 Ma granites
Seven samples of the Kulpitjata Granite Complex from AYERS ROCK were dated, six by the SHRIMP U-Pb zircon method and one by the Kober evaporative Pb-Pb method. The U-Pb dates are in the range 1197-1150 Ma, and probably record the age of igneous crystallisation. Two samples (A94/644 and BJ96/220) have zircon with older 1550 Ma cores. The evaporative method was used to date an altered and deformed, iron-rich, sul de-bearing sample of Katiti Granite (MP94/503) and a date of 1172 ± 4 Ma has been obtained. A SHRIMP U-Pb zircon date of 1159 ± 20 Ma was reported by Camacho and Fanning (1995) for a sample of Yununba Granite (MP5) from MULGA PARK. This date was revised to 1159 ± 10 Ma by Camacho 1997.
For this study, ve other samples of the Kulpitjata Granite Complex were dated using the SHRIMP U-Pb zircon method by NTGS in collaboration with CM Fanning of PRISE 9. Samples A92/10A and A94/1402 are of medium to coarse deformed granites, and these have been dated at 1150 ± 19 Ma and 1197 ± 21 Ma, respectively. A third sample from Allanah (A94/644) is strongly deformed and has yielded an interpreted igneous crystallisation age of 1191 ± 55 Ma (reconnaissance data). Sample BJ96/277A from an isolated outcrop in northern BRITTEN JONES is of a rare undeformed, medium porphyritic granite and this has been dated at 1182 ± 27 Ma. A ne granite from Kelly Hills contains zircon dated at 1181 ± 34 Ma (sample BJ96/220).
1050 Ma magmatism
A sample of an unaltered and undeformed porphyritic rhyolite clast from the Mount Currie Conglomerate (sample O94-57F) returned a date of 1062 ± 6 Ma, using the Kober Pb-Pb evaporation technique (analysis provided for NTGS by J Foden at Adelaide University). The Nulchara Charnockite has been dated at 1044 ± 5 Ma and the Mitchell Nob Granite at 1068 ± 6 Ma (Camacho 1997).
SM-ND ISOTOPIC DATA
Samarium-neodymium isotopic determinations of the Allanah Gneiss, granulite granitic gneiss and Kulpitjata Granite Complex have depleted mantle model ages in the range 1.60-1.97 Ga. This indicates a largely Proterozoic precursor (Appendix 2e).
K-AR AND RB-SR ISOTOPIC DATA
K-Ar and Rb-Sr analyses have constrained the age of Petermann Orogeny deformation in southeastern AYERS ROCK to about 560-530 Ma (Camacho and Fanning 1995; see also Camacho 1997).
GEOLOGICAL HISTORY
The following is a brief synopsis of the geological evolution in AYERS ROCK. Dates are approximate.
1590-1550 Ma: Emplacement of granitic plutons and related felsic volcanic rocks took place into an unidenti ed protolith. These rocks, along with remnants of older metasediments, formed the protolith for the Allanah Gneiss and granulite facies felsic gneiss. Inherited zircon cores have ages of 1700 Ma and 2000 Ma. Camacho (1997) suggested that amphibolite facies metamorphism may have accompanied this magmatism at about 1550 Ma.
1200-1170 Ma: The Musgravian Event affected mainly granitic and lesser sedimentary crust, and resulted in deformation and amphibolite to granulite facies metamorphism. The Musgrave Block and the Albany-Fraser belt in Western Australia, form part of the worldwide Grenville Belt of tectonism and magmatism (Myers et al 1996). In a global context, the period 1300-1000 Ma was marked by the amalgamation of landmasses to form the Rodinia supercontinent. In addition, Myers et al suggested the convergence of a southern landmass (Gawler Craton) and a northern landmass (North Australian Craton) at this time.
1170-1130 Ma: Extensive granite magmatism, syn- or slightly post-metamorphism. Multiple plutons of the Kulpitjata Granite Complex were intruded, in many places as sheet-like bodies. Several granite suites of similar age were intruded to the west in PETERMANN (Scrimgeour et al 1999), to the east in KULGERA (Edgoose et al 1993) and to the south in WOODROFFE (Camacho 1997).
1080-1050 Ma: Further felsic and ma c magmatism. The Michell Nob Granite, Nulchara Charnockite and Alcurra Dyke Swarm were intruded in AYERS ROCK, as were dykes that are correlated with basalts of the Tollu Group. The ma c-ultrama c Giles Complex (Glikson et al 1995, 1996) was emplaced in the western Musgrave Block.
850-800 Ma: Subsidence and deposition to form the Amadeus Basin. The Dean Quartzite, Pinyinna beds and Bitter Springs Formation were initially deposited. Intrusion of the 820 Ma Amata Dyke Swarm was probably related to extension associated with the basin (Zhao and McCulloch 1993, Zhao et al 1994).
800-560 Ma: Deposition of younger units within the Amadeus Basin, including the Inindia and Winnall beds.
560-530 Ma: A major intraplate event, the Petermann Orogeny, caused extensive deformation and metamorphism. Basement gneiss was mylonitised and interthrusted with the Dean Quartzite and Pinyinna beds. Granulite facies rocks of the Fregon subdomain were thrust over amphibolite facies rocks of the Mulga Park subdomain.
9 Precise Radiogenic Isotope Services, Research School of Earth Sciences, Australian National University, Canberra.
30
560-530 Ma: Syn-orogenic uvial sediments were deposited in piedmont settings, to form the Mount Currie Conglomerate and Mutitjulu Arkose.
490-430 Ma: Deposition of Ordovician marine sediments of the Larapinta Group, which includes the Stairway Sandstone, Stokes Siltstone and Carmichael Sandstone.
400-300 Ma: Compression during the Alice Springs Orogeny lead to further folding and crust-penetrative thrust faulting of the Amadeus Basin and Musgrave Block.
ECONOMIC GEOLOGY
Hydrocarbons
The Amadeus basin succession is prospective for oil; Weste (1989) and Roe (1991) have provided petroleum and gas exploration summaries. The most recent exploration well was Murphy 1 by Paci c Oil and Gas (Menpes 1991), which was drilled in central KULGERA and failed to encounter any hydrocarbons. Seismic surveys have been conducted in northeastern AYERS ROCK (Ripper and Smith 1982, Menpes 1990) and an aeromagnetic survey has been carried out to delineate structure (Wyatt 1983).
Phosphate
Wells et al (1970) noted the presence of phosphate pellets within a coarse horizon of the Stairway Sandstone to the northeast of Curtin Springs. These are also known from Sunday Range in KULGERA (Edgoose et al 1993). The occurrence is limited in extent and appears to be of little economic importance.
Zeolites
Zeolites occur in recent sediments of the playa lake system and the economic potential has been investigated. Spring Lake to the east of Curtin Springs carries the greatest concentration, but no commercial opportunity is evident on current information.
Metalliferous potential
Clarke and Moore (1979) summarised the mineral occurrences of the Uluru-Lake Amadeus region. Wyborn et al (1996) suggested that the Musgrave Block granites have some potential for Cu-Au-Fe deposits. Viridine-bearing schist in the southern Kelly Hills is possibly indicative of an original manganiferous sediment.
Mineralisation has not been recorded from AYERS ROCK, but copper sulfide is recorded from granulite rocks in South Australia. Drilling by MESA in 1971 on the Kenmore 11 prospect in South Australia encounted sub-economic minerals, chie y pyrite, chalcopyrite and minor molybdenum. This occurs in a 5 m wide band that is conformable with gneissic banding over a strike length of 450 m and is uniform in width and grade. Immediately to the west at Kenmore 1, coincident geochemical and induced
polarization anomalies have been delineated. Pain and Hiern (1973) consider that the sul de mineralisation was originaly strata-bound. This is the only mineralisation of this type known from the Musgrave Block.
Groundwater
Many water bores have been drilled in AYERS ROCK, most of which are concentrated in the Yulara-Uluru area in an effort to nd water for the tourist town of Yulara. Most bores were sited with little geological input and encounted low supplies of unsuitable quality. The current water supply for Yulara is drawn from the Dune Plains Bore eld and requires treatment to reduce dissolved salts. In the vicinity of Uluru, good quality water has been encountered. Water bores are also located in the east on pastoral properties. On Curtin Springs Station, shallow water bores successfully provide stock with water from calcrete horizons (Jacobson et al 1989). On Mulga Park Station, bores drilled in crystalline basement rocks provide suf cient stock water. Elsewhere in AYERS ROCK, bores have been drilled primarily to provide water for Aboriginal outstations. Logs and cuttings of water drillholes are kept in the Alice Springs of ce of Department of Lands, Planning and Environment. Summary reports were provided by Read (1978), Jolly (1979), Knott (1981) and Jacobson et al (1989).
ACKNOWLEDGEMENTS
The authors gratefully acknowledge the Traditional Owners of Mutitjulu, Amata and other Pitjantjatjara communities for access to their land, and the Central Land Council eld of cers Andrew Morris and Gordon Williams, who provided untiring help. Max Heggen of the DME provided great support in negotiating access. Assistance was given by pastoral leaseholders Neville and Ann Nicole of Mulga Park, and Peter and Ashley Severin of Curtin Springs.
We thank staff of the Australian Nature Conservation Agency at Uluru, including Jake Gillen; staff of the Natural Resources Division, Department of Lands, Planning and Environment, Alice Springs, for providing drillhole data; and Andrew Hill of Macquarie University for 13C analysis of the Bitter Springs Formation. We acknowledge discussions with geologists from Geoscience Australia and PIRSA10 Minerals and Energy Resources, including Gladys Warren, John Sheraton, Ian Sweet, Gerry Jacobson, Colin Conor, Sue Daly, Ian Dyson and Wolfgang Preiss. Our thanks go to Gresley Wakelin-King for editing the Cenozoic section and to Dennis Gee, Chris Edgoose and Barry Pietsch for comments on the manuscript. Many of the SHRIMP U-Pb dates discussed in Geochronology were determined on a collaborative basis by Mark Fanning at PRISE. The manuscript was edited by Tim Munson and formatted by Stephen Cox.
Finally, we thank numerous NTGS staff, including Dorothy Close, Nigel Donnellan, Chris Edgoose and Ian Scrimgeour, for useful discussions; Carmel Leonard, Jacinta McKinley, Chris Jamieson, Michelle Braham, Peter Snepp and colleagues for administrative support; Kerry Slater for
10 Department of Primary Industries and Resources South Australia.
31
geophysical interpretation; Martin Cardona for coordinating eld staff and equipment; Chris Field, Peter Crispe and other NTGS eld staff for their patience in the bush; and Richard Jong, Jann and David Lambton-Young, Helen Richmond, Phil Carter, Sandy Carter, Grecian Dempster, Gary Andrews and others in the NTGS Cartographic section for producing the map and gures.
Authorship: This report was commenced and the eld project managed by Nigel Duncan, whose original draft manuscript is available in digital NTGS archives. After Nigel left NTGS in June 1998, the manuscript was revised and completed by David Young. Alfredo Camacho contributed suggestions to the project and provided mapping on Mulga Park. Phil Ferenczi and Tania Madigan contributed to mapping in the MOUNT OLGA and ALLANAH sheets, respectively.
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APPENDIX 1 - De nitions of new stratigraphic names
Allanah Gneiss
Proposer: DN Young
Derivation of name: Allanah Hill, central ALLANAH, AYERS ROCK.
Distribution: Small outcrops throughout southern AYERS ROCK, Northern Territory.
Type area (GDA94 datum): Around AMG 659847mE, 7151385mN (25°44'48.6"S 130°35'37.5"E) in southwestern ALLANAH, AYERS ROCK.
Lithology: Non-porphyritic, ne to medium granitic gneiss, migmatitic in places. It is dark grey on fresh surfaces and typically contains biotite and muscovite. Exposures vary from low to rounded hills that contain prominent tors and pavements. Minor components include small lenticular bodies of amphibolite and pelitic gneiss in southern MULGA PARK. Amphibolite is black-green and ne- to medium-grained. Pelite is weathered in outcrop and contains quartz, K-feldspar, plagioclase, garnet, biotite and muscovite; alternating bands of migmatitic veins and biotite-rich layers de ne the foliation.
Structural attitude: Gneissic layering probably resulted from deformation during the 1200 Ma Musgravian Event. In places, it is strongly overprinted by a younger mylonitic fabric of the Petermann Orogeny. The gneissic fabric in some outcrops appears to be planar, although elsewhere there is some open to tight folding of the fabric. Many outcrops have undergone partial melting and are slightly to extensively migmatitic. In some outcrops, leucosome veins cut the gneissic foliation and are commonly subparallel to later upright fold axes. Minerals present include quartz, K-feldspar, plagioclase, biotite and garnet. Superimposed on the gneissic fabric are zones of intense mylonitic deformation associated with the Petermann Orogeny. Crystallisation of new grains of garnet, muscovite, sphene and epidote is con ned to these zones.
Relationships and boundary criteria: Occurs as large outcrops but more commonly as rafts or xenoliths within the more voluminous Kulpitjata Granite Complex (1200-1150 Ma), which intrudes it.
Age and evidence: A sample of Allanah Gneiss (A94/1378, later resampled for geochemical analysis as A97/1378) from southwestern AYERS ROCK contains magmatic zircon rims on inherited cores, giving an interpreted igneous crystallisation age of 1591 ± 30 Ma and inherited core ages of 1700 Ma. To the east a similar sample (A93/63) contains zircon dated at 1539 ± 23 Ma, with no discernible rims or inherited cores. Amphibolite facies granitic gneiss from MULGA PARK (MP43) has zircons dated at 1554 ± 23 Ma, interpreted as the age of igneous crystallisation, as well as one 2000 Ma core (Camacho and Fanning 1995). There are also 1206 ± 23 Ma metamorphic overgrowths, interpreted as re ecting the Musgravian Event. Another sample of this gneissic unit, also from southeastern AYERS ROCK (MP98), has 1563 ± 15 Ma rims on cores of unknown age (Camacho 1997). Camacho carried out U-Pb monazite work on this sample and obtained a metamorphic age of 1177 ± 6 Ma.
Synonomy: Includes rocks previously mapped by Camacho (1991) as Mulga Park Gneiss in MULGA PARK, as well as outcrops designated as amphibolite facies gneiss in generalised maps by Camacho and Fanning (1995) and Camacho et al (1995).
Correlatives: Probably correlates with other 1550 Ma granitic gneisses of the Musgrave Block, including granulite facies granitic gneiss mapped on AYERS ROCK, and granitic gneiss described by Camacho and Fanning (1995) and Camacho (1997). It is also possible that granitic gneiss of the former Mulga Suite in MULGA PARK (Camacho 1991) may correlate with the Allanah Gneiss.
Katiti Granite
Proposer: DN Young
Derivation of name: Katiti Aboriginal Land Trust area, AYERS ROCK.
Distribution: Localised in southeastern AYERS ROCK
Type area (GDA94 datum): Around locality MP94/503 (AMG 763497mE, 7137075mN: 25°51'39.4"S 131°37'45.5"E).
Lithology: Granite is grey to pink when fresh, medium-grained, porphyritic and has a strong mylonitic fabric de ned by thin anastamosing bands of green biotite (Camacho 1991). Porphyroblasts of K-feldspar up to 3 mm remain within the fabric and are relict magmatic grains. In high-strain zones, plagioclase is extensively altered to ne, randomly oriented muscovite, epidote and green biotite. Accessory amphibole, apatite and zircon occur within biotite-rich bands.
Structural attitude: Features a variable mylonitic fabric imposed during the Petermann Orogeny.
Relationships and boundary criteria: Intrudes the 1550 Ma Allanah Gneiss and Opparinna Memtamorphics; cut by dolerite dykes that are 1080 Ma in age.
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Age and evidence: The Kober evaporative method was used to obtain a date of 1172 ± 4 Ma for an altered and deformed, iron-rich, sul de-bearing sample of Katiti Granite (MP94/503).
Synonomy: Forman (1965) mapped The Katiti Granite, along with other parts of the Kulpitjata Granite Complex, as Precambrian granite or undivided granite and gneiss.
Correlatives: Correlates with numerous other granite suites of 1200-1150 Ma age in the northern Musgrave Block, including the Mantarurr, Pottoyu and Umutju Granite Suites in PETERMANN RANGES (Scrimgeour et al 2000).
Kulpitjata Granite Complex
Proposer: DN Young
Derivation of name: Kulpitjata Sacred Site, eastern BRITTEN JONES, AYERS ROCK.
Constituent units: Yununba Granite, Katiti Granite and undivided Kulpitjata Granite Complex.
Distribution: Extensive throughout southern AYERS ROCK, Northern Territory.
Type area (GDA94 datum): For undivided Kulpitjata Granite Complex: around locality A93/63 (AMG 679427mE, 7138215mN; 25°51'48.4"S 130°47'26.5"E), ALLANAH. Reference localities: A94/644 (674967mE, 7153615mN; 25°43'40.5"S 130°44'29.6"E), BJ96/220 (743327mE, 7140655mN; 25°49'55.8"S, 131°25'39.2"E) and BJ96/277A (737627mE, 7161665mN; 25°38'36.7"S 131°22'01.1"E).
Lithology: Comprises mainly biotite granite and sheared derivatives (mylonitic granitic gneiss and schist), plus lesser hornblende granite, aplite, pegmatite and granitic dykes, and quartz veins. Includes two formal units in MULGA PARK: Yununba Granite and Katiti Granite (Camacho 1991). The majority of outcrops mapped as Kulpitjata Granite Complex are probably about 1150 Ma in age, but due to incomplete access and a strong deformational overprint in places, it is possible that mapping of the unit has included some areas of older or younger granitic material (eg 1550 Ma Allanah Gneiss or 1050 Ma granites).
Structural attitude: Rarely undeformed; generally features a variable mylonitic fabric imposed during the Petermann Orogeny. Some extremely sheared outcrops have been converted to two-mica schist due to the breakdown of feldspar.
Relationships and boundary criteria: Intrudes the 1550 Ma Allanah Gneiss and the Opparinna Memtamorphics; cut by dolerite dykes that are 1080 Ma in age.
Age and evidence: Seven samples of Kulpitjata Granite Complex from AYERS ROCK were dated, six by the SHRIMP U-Pb zircon method and one by the Kober evaporative Pb-Pb method. The U-Pb dates are in the range 1197-1150 Ma and are thought to record the age of igneous crystallisation. Two samples (A94/644 and BJ96/220) have zircon with older 1550 Ma cores. The evaporative method was used for MP94/503, an altered and deformed, iron-rich, sul de-bearing sample of Katiti Granite, and this gave a date of 1172 ± 4 Ma. A SHRIMP U-Pb zircon date of 1159 ± 20 Ma was reported by Camacho and Fanning (1995) for a sample of Yununba Granite from MULGA PARK (MP5). This date was revised to 1159 ± 10 Ma by Camacho (1997).
Five other samples of Kulpitjata Granite Complex were dated by the SHRIMP U-Pb zircon method as part of this study, by NTGS in collaboration with CM Fanning of PRISE (Australian National University). Samples A92/10A and A94/1402 are medium to coarse deformed granites, and have yielded dates of 1150 ± 19 Ma and 1197 ± 21 Ma, respectively. A third sample from ALLANAH (A94/644) is strongly deformed and gave results interpreted as indicating the age of igneous crystallisation at 1191 ± 55 Ma. Sample BJ96/277A, from an isolated outcrop in northern BRITTEN JONES, is a rare undeformed, medium porphyritic granite and gave a date of 1182 ± 27 Ma. A ne granite from Kelly Hills was dated at 1181 ± 34 Ma (sample BJ96/220).
Synonomy: Mapped by Forman (1965) as Precambrian granite or undivided granite and gneiss.
Correlatives: Outcrops of this complex in western AYERS ROCK may correlate with the Mantarrur Suite of Scrimgeour et al (1999).
Mutitjulu Arkose
Proposer: DN Young
Derivation of name: Mutitjulu community, 2 km east of Uluru, AYERS ROCK, Northern Territory.
Distribution: Limited distribution in northwestern AYERS ROCK.
Type section (GDA94 datum): At Uluru (Ayers Rock), the famous inselberg and tourist destination. Section youngs to the southwest: base at 705027mE, 7295965mN (24°26'10.8"S 131°01'20.8"E), top at 704127mE, 7294265mN (24°27'06.5"S 131°00'49.7"E).
Thickness: Approximately 2400 m.
Lithology: Classi ed as arkosic arenite using the scheme of Pettijohn et al (1973). Sweet (pers comm 1994) reported an average
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composition of 50% feldspar, 25-35% quartz and up to 25% rock fragments. Freshest material at Uluru is found under overhangs and is grey, with pink or green tinges. Sweet (pers comm 1994) recognised four rock facies, based on lithology, grainsize and sedimentary structures. These are: well sorted, planar bedded or ripple laminated, very ne to medium sandstone; trough crossbedded sandstone to granule conglomerate; planar bedded and crossbedded granule to pebble conglomerate; and massive conglomerate. The trough crossbedded sandstone to granule conglomerate facies is the most common. Sweet (pers comm 1994) reported that ner arkosic beds are well sorted and generally darker in colour, re ecting a higher content of opaque minerals, and coarser arkosic beds are poorly sorted and grade into pebble conglomerate (pebbles up to 40 mm).
In thin section, K-feldspar and quartz are dominant, and there are minor plagioclase, opaques, microclasts of basalt and rare grains of probable rhyolite, orthopyroxene and sphene. Clasts and grains are in the range 2-4 mm and are set within a matrix of polycrystalline quartz. Grains are angular to subangular and are closely packed. K-feldspar occurs as angular to subangular perthitic grains. Quartz is angular and only lightly dusted with inclusions. Rare spherical grains are interpreted to be quartz amygdales from basalt. Plagioclase occurs both as individual subrounded grains and as highly altered inclusions within K-feldspar. Basalt clasts are subrounded and have a quenched texture. They are invariably replaced to some degree by chlorite and epidote.
Sedimentary features include multidirectional crossbedding, scour and ll troughs and ripples. These indicate a high-energy uvial environment of broad shallow channels or sheet oods. Sweet (pers comm 1994) interpreted the fourfold facies as re ecting progressively higher energy of transport. Massive conglomerate facies may have resulted from debris ow. Grainsize appears to coarsen to the southwest (upwards in the section).
Structural attitude: Dips very steeply to the southwest at 85°.
Relationships and boundary criteria: None exposed. Presumed to unconformably overlie Neoproterozoic strata of the Amadeus Basin including Dean Quartzite, Pinyinna beds, Inindia beds and Winnall beds.
Age and evidence: No fossils known. Considered to be synchronous with the 560-530 Ma Petermann Orogeny.
Synonomy: Included as part of the Mount Currie Conglomerate by Forman (1965); informally named Uluru Arkose by Sweet and Crick (1992).
Correlatives: Probably equivalent to the nearby middle or upper units of the Mount Currie Conglomerate, both of which contain largely igneous detrital material.
Opparinna Metamorphics
Proposer: DN Young
Derivation of name: Opparinna Creek, southeastern BRITTEN JONES, AYERS ROCK.
Distribution: Limited extent in southern Kelly Hills, BRITTEN JONES.
Type section (GDA94 datum): base (assuming no overturning) at AMG 741227mE, 7130565mN (latitude 25°55'27.5"S, longitude 131°24'30.4"E), top at 741527mE, 7130665mN (25°55'21.3"S 131°24'41.2"E). Reference section: base at 741427mE, 7128165mN (25°56'42.6"S 131°24'39.2"E), top at 741827mE, 7128265mN (25°56'39.1"S 131°24'53.5"E).
Thickness: Approximately 85 m maximum.
Lithology: A lower andalusite schist (including green, manganese-rich andalusite) is overlain by quartzite and then conformably by meta-igneous amphibolite. Andalusite schist occurs as a layer up to 30 m thick that overlies sheared granitic gneiss of the Kulpitjata Granite Complex. The schist contains muscovite, quartz, viridine and opaques. Muscovite is straw coloured and occurs as subparallel lamellae and disseminated akes. Fine opaques and anhedral irregular viridine are generally associated with the lamellae. Viridine (Mn-rich andalusite) forms up to 15% of thin sections examined, and occurs as medium to coarse, strongly poikilitic porphyroblasts and as ne anhedral grains located at the margins of quartz grains. The porphyroblasts have highly irregular margins and numerous inclusions of very ne quartz, muscovite and black opaques in parallel sigmoidal trails.
A resistant quartzite overlies the andalusite schist and has a maximum thickness of 15 m. It is strongly foliated but relict bedding is visible. It contains quartz, muscovite, opaques and accessory euhedral spessartine garnet and anhedral piemontite. Traces of microcline and zircon are present.
Amphibolite occurs as a body 50 m thick that is interleaved with the underlying quartzite, due to interlayering or shearing. The amphibolite is dark grey to green, massive, ne-gained and equigranular. It is composed mainly of hornblende, lesser plagioclase, and minor quartz and titanite. Accessory opaques, pyrite and apatite are also present. Coarse granite and pegmatite dykes intrude all rock types and are mainly sub-parallel to the layering and foliation. These dykes are probably part of the Kulpitjata Granite Complex. The protolith was basalt or dolerite.
Structural attitude: Beds dip to the east at about 15°. A strong schistosity or foliation is present.
Relationships and boundary criteria: Appears to overlie sheared granite of the 1200-1150 Ma Kulpitajata Granite Complex, but is cut by dykes of granite and pegmatite, presumably related to that Complex. The Opparinna Metamorphics are probably a large xenolithic body or roof pendant within the extensive granite.
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Age and evidence: Zircons from a sample of quartzite have yielded an age of 1603 ± 36 Ma, which is a maximum age of deposition. A minimum age of 1150 Ma is provided by intruding dykes of the Kulpitjata Granite Complex.
Synonomy: The Opparinna Metamorphics were rst mapped as undivided Precambrian schist and gneiss by Forman (1965).
Correlatives: None known.
Yununba Granite
Proposer: DN Young
Derivation of name: Yununba Hill, southeastern MULGA PARK, AYERS ROCK.
Distribution: Limited extent in southeastern AYERS ROCK.
Type locality (GDA94 datum): Yununba Hill (AMG 778927mE, 7126165mN: 25°57'23.3"S 131°47'07.6"E).
Lithology: Comprises strongly foliated, medium, variably porphyritic granite that grades to coarse, strongly porphyritic granite. It is typically grey to white on fresh surfaces and contains crystals of elongate white K-feldspar up to 2 cm long, and plagioclase and quartz up to 1 cm. The groundmass comprises quartz, feldspars, biotite, secondary muscovite and accessory apatite, zircon, magnetite, ilmenite, allanite and sphene. Fluorite occurs in places, as does metamorphic garnet.
Aplite and pegmatite dykes are uncommon. Late joints cut the foliation and in places are lled with epidote. The foliation is mylonitic and de ned by a penetrative, shallowly dipping anastamosing schistosity, which in places wraps around lower-strain boudins up to 30 m across.
Structural attitude: Features a variable mylonitic fabric imposed during the Petermann Orogeny.
Relationships and boundary criteria: Intrudes the 1550 Ma Allanah Gneiss and the Opparinna Memtamorphics; cut by dolerite dykes 1080 Ma in age.
Age and evidence: A SHRIMP U-Pb zircon date of 1159 ± 20 Ma was reported by Camacho and Fanning (1995) for a sample of Yununba Granite (MP5). This date was revised to 1159 ± 10 Ma by Camacho 1997.
Synonomy: Forman (1965) mapped the Yununba Granite, along with other parts of the Kulpitjata Granite Complex, as Precambrian granite or undivided granite and gneiss.
Correlatives: Correlates with numerous other granite suites of 1200-1150 Ma age in the northern Musgrave Block, including the Mantarurr, Pottoyu and Umutju Granite suites in PETERMANN RANGES (Scrimgeour et al 2000).
40
APPENDIX 2a - Geochemical analyses of gneiss, granite, charnockite and rhyolite clasts from AYERS ROCK; Allanah – Allanah Gneiss; Michell – Michell Nob Granite; Nulchara – Nulchara Granulite; Mt Currie – Mount Currie Conglomerate
Sample No A97/1378 MP97/43 BJ96/280 MP97/513 MP94/501 MP2 MP94/500 O95/57F O95/57G O95/57H
Unit Allanah Allanah granulite granulite Michell Nulchara Nulchara Mt Currie Mt Currie Mt Currie
E GDA94 659847 782027 740777 766789 774397 775127 773837 659877 659877 659877 N GDA94 7151385 7122565 7156365 7124588 7122115 7121565 7121965 7208615 7208615 7208615
SiO2 70.10 71.90 69.30 71.30 67.20 65.00 63.40 72.00 75.50 75.60 TiO2 0.36 0.41 0.71 0.42 0.57 0.92 1.00 0.32 0.24 0.25 Al2O3 14.00 13.70 13.70 14.30 15.90 14.40 14.50 12.30 12.10 12.10 Fe2O3 3.38 2.78 4.64 3.46 4.62 6.10 7.67 5.19 1.96 1.74 FeO 1.00 1.40 2.30 1.70 2.70 - 4.60 0.50 0.30 0.30 MnO 0.06 0.08 0.14 0.15 0.11 0.15 0.17 0.29 0.03 0.04 MgO 0.96 0.71 0.99 1.08 0.41 1.24 1.43 0.17 0.18 0.18 CaO 1.99 1.71 3.12 2.55 2.24 3.50 3.90 0.72 0.35 0.35 Na2O 3.09 2.63 2.83 2.97 3.78 3.26 3.31 3.03 2.75 2.91 K2O 3.94 5.36 4.10 3.44 5.81 4.40 4.46 5.98 6.20 6.16 P2O5 0.09 0.12 0.25 0.08 0.14 0.29 0.29 0.03 0.02 0.02 F 0.06 0.08 0.09 0.07 0.09 - 0.09 0.02 0.02 0.01 LOI 0.81 0.20 0.35 0.37 0.00 0.30 0.00 0.55 0.43 0.23 Total 98.84 99.68 100.22 100.19 100.87 99.56 100.21 100.60 99.78 99.59
La 25 45 40 34 65 70 60 98 90 98Ce 52 96 77 85 155 125 135 180 155 160Pr 7 13 9 10 16 - 16 21 15 20Nd 27.5 55 36 41.5 90 - 85 92 66 83Sm 4.5 8 4.5 6 14 - 15 14.5 10.5 10Eu 1 1.5 2 1 4.9 - 4.3 2 1 1Gd 3 5 7 4 13 - 14 15 11 11Tb 0.5 1 1 0.5 2.1 - 2.2 2.5 2 2Dy 3.5 4.5 6.5 5 13 - 14 14 10 12.5 Ho 0.5 0.5 1.5 1 2.5 - 2.6 3.5 3 3Er 2 2 4 3 6.2 - 5.8 9 9 8Tm 0.5 0.5 0.5 0.5 1 - 1.1 1 1 1Yb 2 1 4 3 6 - 7.2 9 9 10Lu 0.25 0.25 0.5 0.5 1 - 0.9 1.5 1.5 1.5 Sc 5 5 15 10 - - - 5 5 5Y 15 15 35 24 45 58 59 70 66 61Th 7.5 9.5 10 12 11 10 3.7 45 64 68U 1 1 1.5 0.5 1.1 1 0.6 7.5 7 9.5 Zr 155 170 250 150 430 420 410 620 300 300Hf 20 20 15 20 20 - 6 25 20 20Nb 9 9 15 7 20 17 20 33 41 43Rb 130 200 145 135 200 135 140 280 380 360Ba 950 800 880 700 1380 1480 1380 780 500 400Sr 260 160 185 200 180 210 200 45 28 25Cs 4 1.5 1.5 1.5 2.6 - 0.9 1.5 1.5 1.5 V 60 40 60 60 16 - 95 10 5 5Cr 40 40 20 40 5 - 9 460 120 100Ni 6 5 7 9 1 - 16 1 7 1Cu 15 41 1 45 6 - 40 66 42 180Zn 37 43 69 34 90 - 125 40 46 53Mo 2 3 1 3 0.9 - 1 6 3 3Ag 0.5 0.5 0.5 0.5 0.5 - 0.9 0.5 0.5 0.5 Ta - - - - 2 - 6 2 3 3 W - - - - 8 - 5 2.5 5 2.5 Ga 15 17 15 17 23 22 23 6 9 8Ge 1 1 1 1 1 - 1 1 1 1Sn 5 9 1 5 2 - 2 5 5 6Pb 20 30 35 25 40 28 25 15 50 15Bi 1.5 1.5 1.5 1.5 0.1 - 0.1 1.5 1.5 1.5
41
APPENDIX 2b - Geochemical analyses of Kulpitjata Granite Complex from AYERS ROCK
Sample No MP94/502 MP94/503 BJ92/12B A93/10A A93/20 A93/27 A93/46 A93/63 A93/88 A93/223 A93/239 A93/292
E GDA94 778807 763497 714127 689157 683847 685857 688407 679427 681637 687147 686167 681567 N GDA94 7126265 7137075 7152965 7138695 7138615 7136405 7135115 7138215 7137915 7130875 7128935 7122725
SiO2 71.70 66.90 65.30 65.10 75.20 70.60 66.20 71.70 69.50 71.20 66.00 66.10 TiO2 0.42 0.68 1.09 0.63 0.26 0.33 0.66 0.46 0.61 0.37 0.93 0.89 Al2O3 13.80 14.80 14.10 15.50 13.20 15.20 14.80 14.00 14.20 13.30 14.00 13.80 Fe2O3 1.63 2.87 4.01 1.44 1.13 0.83 3.18 1.68 2.20 0.00 3.64 3.45 FeO 1.50 1.85 2.35 3.90 0.55 1.70 2.05 1.90 2.00 2.55 2.00 2.20 MnO 0.11 0.14 0.15 0.15 0.06 0.08 0.06 0.14 0.12 0.09 0.14 0.19 MgO 0.52 1.24 1.27 0.50 0.27 0.57 1.19 0.62 0.79 0.38 1.05 0.91 CaO 1.41 2.53 3.13 2.40 1.49 1.82 2.10 2.26 2.06 1.17 2.64 2.58 Na2O 2.87 3.24 3.04 3.46 3.22 3.77 3.01 3.05 2.72 2.69 2.93 2.84 K2O 6.19 5.14 4.25 6.67 4.97 5.05 5.73 4.21 6.06 6.11 5.15 5.24 P2O5 0.13 0.29 0.30 0.15 0.05 0.12 0.26 0.08 0.25 0.08 0.37 0.40 F 0.19 0.22 0.15 0.40 0.08 0.06 0.12 0.09 0.29 0.14 0.32 0.26 LOI 0.46 1.10 1.10 0.68 0.49 0.51 1.29 0.38 0.04 2.94 0.87 0.52 Total 100.93 101.00 100.24 100.98 100.97 100.64 100.65 100.57 100.84 101.02 100.04 99.38
La 180 90 40 80 45 60 115 35 165 155 190 100Ce 380 200 85 200 105 130 240 80 390 300 320 310Pr 30 20 14 25 11 12 20 9.6 50 30 39 30Nd 140 85 65 110 50 45 65 40 195 90 140 125Sm 15 13 11 19 7.6 7.8 9.8 6.6 30 8.2 22 17Eu 1.6 2.6 2.6 3.9 1.3 1.1 1.6 1.3 2.6 1.2 2.5 3.2 Gd 8.6 11 11 16 8.8 6 6 5 25 5.2 16 14Tb 1 1.4 1.4 2 1.1 0.7 0.7 0.8 3.4 0.7 2 1.9 Dy 3.9 7.8 10 12 9.6 3.7 3.5 5.2 18 4 10.5 13Ho 0.6 1.3 1.5 1.8 1.5 0.5 0.6 0.9 3.3 0.7 3 2.1 Er 2.5 4.2 5.4 5.8 5.6 1.2 1.4 2.7 10 2.5 7 7.2 Tm 0.5 0.6 0.7 0.7 0.7 0.1 0.2 0.4 1.4 0.5 1 1.2 Yb 4.9 3.4 4.5 4.8 4.8 0.7 1.7 2.2 8.6 3.4 7 8.6 Lu 1 0.6 0.7 0.8 0.8 0.1 0.3 0.4 1.2 0.5 1 1.7 Sc - - - - - - - - - - 10 -Y 25 30 30 40 35 11 16 20 75 20 78 65Th 55 30 9.6 13 20 55 17 13 85 70 44.5 12U 6.6 5 3 2.3 2.3 8 0.6 1.9 1.8 8.8 4.5 2.8 Zr 380 240 320 630 130 240 330 190 520 250 520 360Hf 10 10 2 20 7 6 25 9 15 10 25 9Nb 25 18 20 35 19 16 15 11 30 20 28 35Rb 410 270 200 240 230 270 260 210 390 380 300 280Ba 790 1220 1020 1300 400 740 1350 790 840 55 1300 1950Sr 200 360 250 130 115 260 420 125 160 115 300 400Cs 15 35 13 4.8 3.1 3.7 4 25 3.9 7.4 4 5.2 V 25 70 150 7 10 20 25 30 40 13 80 60Cr 1 7 6 2 4 3 16 65 4 11 25 1Ni 2 7 35 1 2 1 8 6 3 1 8 3Cu 16 20 30 4 3 7 25 4 35 4 25 16Zn 60 60 95 140 25 50 55 45 85 40 86 95Mo 0.7 1.5 1.5 1.2 0.3 0.05 0.1 0.8 0.5 2 1 1.8 Ag 0.4 0.4 0.4 0.3 0.5 0.4 0.3 0.4 0.5 0.4 0.5 0.5 Ta 2 2 2 2 2 2 2 2 2 2 - 2W 4 30 2 2 2 2 6 8 2 2 2.5 4Ga 18 18 21 24 16 22 19 17 19 17 22 21Ge 1 1 1 1 1 1 1 1 1 1 1 1Sn 4 2 1 2 6 4 2 4 5 3 1 4Pb 75 50 30 60 35 45 30 25 65 55 51 30Bi 0.3 0.6 0.4 0.2 0.1 0.1 0.1 0.3 0.1 0.1 1.5 0.2
42
APPENDIX 2b - Continued
Sample No A93/297 A93/1206 A94/340 A94/394 A94/425 A94/540 A94/552 A94/601 A94/644 A94/728A A94/750 A94/839A
E GDA94 679667 681127 680537 691407 694037 658557 665617 664447 674967 664237 666367 669077 N GDA94 7127295 7121365 7130395 7122375 7128215 7163195 7162325 7156185 7153615 7144455 7145985 7143795
SiO2 69.00 64.50 67.90 70.90 64.70 64.30 66.60 68.60 68.60 66.00 70.50 71.50 TiO2 0.50 1.10 0.48 0.47 1.10 1.31 0.61 0.44 0.51 0.81 0.49 0.43 Al2O3 14.00 14.00 14.30 13.60 13.60 13.60 14.80 14.80 14.40 15.50 14.00 14.00 Fe2O3 2.36 4.11 1.60 1.43 3.03 3.94 1.74 1.47 1.80 2.32 1.97 1.08 FeO 1.00 2.30 1.75 1.65 3.35 3.50 2.75 1.55 2.10 2.30 1.90 1.60 MnO 0.08 0.15 0.09 0.08 0.17 0.15 0.06 0.09 0.08 0.10 0.11 0.07 MgO 0.77 1.24 0.73 0.53 1.14 1.23 0.92 0.60 0.70 1.25 1.10 0.84 CaO 1.61 2.99 1.33 1.81 3.21 3.52 2.27 1.83 1.98 3.55 2.28 2.90 Na2O 2.69 2.96 2.60 2.78 2.95 2.90 2.72 3.40 3.39 3.99 3.10 3.10 K2O 6.04 4.83 6.87 5.17 4.54 4.55 5.95 5.67 5.31 3.29 3.57 4.17 P2O5 0.22 0.49 0.27 0.13 0.41 0.42 0.26 0.12 0.14 0.22 0.04 0.10 F 0.18 0.32 0.16 0.08 0.16 0.13 0.17 0.13 0.18 0.12 0.07 0.09 LOI 0.84 0.81 0.63 1.58 0.58 0.69 1.82 0.68 1.60 0.63 0.76 0.38 Total 99.29 99.80 98.71 100.21 98.94 100.24 100.67 99.38 100.79 100.08 99.89 100.26
La 170 165 135 40 75 55 165 115 165 65 310 380Ce 380 340 350 90 195 145 350 260 370 115 30 43Pr 43 44 40 11 18 15 50 25 45 18 125 155Nd 155 160 155 40 75 65 165 90 140 71 17 28.5 Sm 28.5 25.5 25 6.8 15 12 20 13 19 13 3.2 1.5 Eu 1.5 2.5 1.7 1.5 2.7 2.7 3.3 1.3 2.1 2.5 14 19Gd 19 20 18 5.8 13 11 13 9.8 13 9 1.9 2.5 Tb 2.5 2 2.1 0.7 1.4 1.6 1.6 1.4 1.7 1 13 12Dy 12 15 10 4.2 10 10 7.2 8.2 9.2 6.5 2.1 2.5 Ho 2.5 3.5 1.5 0.7 1.6 1.9 1.2 1.4 1.5 1.5 7.2 6Er 6 8 4 1.8 5.4 6 3.1 3.9 3.8 4 1.2 0.5 Tm 0.5 1 0.5 0.3 0.7 0.8 0.4 0.6 0.7 0.5 8.6 5Yb 5 8 2.3 1.6 4.5 5 2.7 3.5 3.4 3 1.7 0.5 Lu 0.5 1 0.4 0.2 0.7 0.9 0.4 0.4 0.6 0.25 - 5Sc 5 10 - - - - - - - 10 65 78 Y 78 99 35 15 45 45 25 35 35 46 12 115Th 115 34.5 145 11 25 9.4 140 65 45 15.5 2.8 4.5 U 4.5 3 2.4 0.8 1.8 1.2 1.8 6.6 1.5 6.5 360 420Zr 420 540 420 220 320 300 450 330 440 320 9 10Hf 10 15 20 8 8 7 7 15 9 10 35 23Nb 23 26 20 12 20 20 4 20 25 21 280 360Rb 360 240 360 240 220 190 240 370 300 180 1950 520Ba 520 1700 580 930 1020 1020 1050 1040 1200 1300 400 120Sr 120 340 105 105 230 190 200 230 200 420 5.2 4Cs 4 1.5 5.4 7.8 5.2 6.4 2.9 7.2 6.4 4 60 40V 40 80 30 20 50 80 40 30 35 60 1 25Cr 25 25 2 8 3 4 7 16 9 25 3 6Ni 6 6 2 3 3 6 6 5 5 5 16 43Cu 43 32 25 7 8 12 20 16 19 16 95 64Zn 64 105 65 40 100 110 80 55 85 75 1.8 3Mo 3 1 0.2 0.2 0.8 0.3 0.8 0.4 1.2 1 0.5 0.5 Ag 0.5 0.5 0.4 0.3 0.4 0.3 0.4 0.4 0.3 0.5 2 - Ta 2 2 2 2 2 2 2 4 2.5 W 2.5 2.5 2 2 2 2 7 2 2 2.5 21 20Ga 20 22 17 17 21 21 20 19 24 22 1 1Ge 1 1 1 1 1 1 1 1 1 1 4 4Sn 4 1 3 1 6 2 1 4 2 3 30 52Pb 52 46 55 30 35 35 45 45 45 34 0.2 1.5 Bi 1.5 1.5 0.1 0.1 0.1 0.2 0.1 0.05 0.1 1.5
43
APPENDIX 2b - Continued
Sample No A94/968 A94/972 A94/1402 A94/2003 BJ96/178 BJ96/201 BJ96/276 BJ96/277A MP96/505 MP96/509 BJ96/280
E GDA94 674577 674507 657787 678597 749327 740407 745027 737627 765127 765385 740777 N GDA94 7147865 7147545 7152635 7147875 7145365 7144335 7125055 7161665 7127165 7127774 7156365
SiO2 72.50 75.00 68.00 67.50 74.60 66.10 74.80 64.40 68.00 68.70 69.30 TiO2 0.53 0.12 0.86 0.71 0.18 0.61 0.15 1.00 0.48 0.48 0.71 Al2O3 13.50 13.00 14.00 14.50 13.40 15.00 13.90 15.30 15.40 15.50 13.70 Fe2O3 1.44 0.68 2.47 1.80 0.70 2.07 0.79 5.78 1.66 1.54 4.64 FeO 1.50 0.02 2.30 3.10 0.50 2.10 0.40 0.50 1.80 1.70 2.30 MnO 0.08 0.06 0.12 0.10 0.04 0.10 0.04 0.15 0.17 0.14 0.14 MgO 0.51 0.14 0.95 0.87 0.21 0.86 0.24 1.22 0.99 1.10 0.99 CaO 1.69 0.98 2.70 2.36 0.97 2.05 1.72 2.70 2.77 2.92 3.12 Na2O 2.80 3.33 3.05 2.92 3.01 2.61 3.00 2.90 3.47 3.69 2.83 K2O 5.44 5.27 4.77 4.91 5.71 6.22 5.07 5.54 4.13 3.72 4.10 P2O5 0.14 0.02 0.28 0.22 0.11 0.34 0.05 0.55 0.19 0.17 0.25 F 0.09 0.24 0.16 0.15 0.06 0.26 0.04 0.44 0.08 0.08 0.09 LOI 0.63 0.65 0.72 0.39 - - - - - - 0.35 Total 100.85 99.51 100.38 99.53 99.49 98.32 100.20 100.48 99.14 99.74 102.52
La 340 350 90 195 145 350 260 370 115 31 40Ce 44 40 11 18 15 50 25 45 18 67 77Pr 160 155 40 75 65 165 90 140 71 6 9Nd 25.5 25 6.8 15 12 20 13 19 13 27.5 36Sm 2.5 1.7 1.5 2.7 2.7 3.3 1.3 2.1 2.5 5 4.5 Eu 20 18 5.8 13 11 13 9.8 13 9 1.5 2Gd 2 2.1 0.7 1.4 1.6 1.6 1.4 1.7 1 7 7Tb 15 10 4.2 10 10 7.2 8.2 9.2 6.5 1.5 1Dy 3.5 1.5 0.7 1.6 1.9 1.2 1.4 1.5 1.5 10 6.5 Ho 8 4 1.8 5.4 6 3.1 3.9 3.8 4 2 1.5 Er 1 0.5 0.3 0.7 0.8 0.4 0.6 0.7 0.5 7 4Tm 8 2.3 1.6 4.5 5 2.7 3.5 3.4 3 1 0.5 Yb 1 0.4 0.2 0.7 0.9 0.4 0.4 0.6 0.25 8 4Lu 10 - - - - - - - 10 1 0.5 Sc 99 35 15 45 45 25 35 35 46 5 15Y 34.5 145 11 25 9.4 140 65 45 15.5 68 35Th 3 2.4 0.8 1.8 1.2 1.8 6.6 1.5 6.5 12 10U 540 420 220 320 300 450 330 440 320 3 1.5 Zr 15 20 8 8 7 7 15 9 10 130 250Hf 26 20 12 20 20 4 20 25 21 10 15Nb 240 360 240 220 190 240 370 300 180 23 15Rb 1700 580 930 1020 1020 1050 1040 1200 1300 210 145Ba 340 105 105 230 190 200 230 200 420 500 880Sr 1.5 5.4 7.8 5.2 6.4 2.9 7.2 6.4 4 300 185Cs 80 30 20 50 80 40 30 35 60 8 1.5 V 25 2 8 3 4 7 16 9 25 50 60Cr 6 2 3 3 6 6 5 5 5 10 20Ni 32 25 7 8 12 20 16 19 16 10 7Cu 105 65 40 100 110 80 55 85 75 1 1Zn 1 0.2 0.2 0.8 0.3 0.8 0.4 1.2 1 56 69Mo 0.5 0.4 0.3 0.4 0.3 0.4 0.4 0.3 0.5 1 1Ag - 2 2 2 2 2 2 2 - 0.5 0.5 Ta 2.5 2 2 2 2 7 2 2 2.5 - - W 22 17 17 21 21 20 19 24 22 - - Ga 1 1 1 1 1 1 1 1 1 18 15Ge 1 3 1 6 2 1 4 2 3 1 1Sn 46 55 30 35 35 45 45 45 34 1 1Pb 1.5 0.1 0.1 0.1 0.2 0.1 0.05 0.1 1.5 15 35Bi 1.5 1.5
44
APPENDIX 2c - Analyses of ma c dykes from AYERS ROCK
Sample BJ96/277B A93/43 MP61 O96/75 A93/214 A93/205 A93/121
E GDA94 737627 688228 768427 667327 688217 688577 682967 N GDA94 7161665 7135675 7117665 7204565 7132005 7132867 7132095
SiO2 49.00 49.10 49.30 53.40 59.10 59.90 60.10 TiO2 1.08 0.99 1.84 1.14 1.41 1.47 1.55 Al2O3 15.10 16.90 15.30 14.60 14.80 14.50 14.30 Fe2O3T 11.50 11.80 14.20 11.80 9.85 9.38 9.62 Fe2O3 3.06 4.80 - 6.13 5.24 3.55 4.95 FeO 7.60 6.30 - 5.10 4.15 5.25 4.20 MnO 0.18 0.19 0.20 0.18 0.16 0.18 0.16 MgO 8.92 7.97 7.50 4.47 3.32 2.98 2.86 CaO 10.60 10.00 7.15 7.59 6.00 5.72 5.54 Na2O 2.19 2.70 3.02 2.72 3.04 3.07 3.00 K2O 0.48 0.51 0.79 2.55 2.56 2.75 2.90 P2O5 0.13 0.10 0.21 0.28 0.32 0.35 0.36 F 0.04 0.01 - 0.05 0.06 0.07 0.06 LOI 1.06 0.52 0.23 1.16 0.22 0.26 0.50 Total 99.44 100.09 99.74 99.37 100.38 100.05 100.48
La 5 5 10 33 35 35 50Ce 10 20 25 61 80 80 135Pr 1 1.3 - 7 8.8 9.6 9Nd 6 7 - 29.5 40 45 40Sm 1 2 - 1.5 8.6 8.6 7.6 Eu 1 0.8 - 2 2.5 2.5 2.8 Gd 2 2.5 - 6 8.8 8.2 7.4 Tb 0.25 0.4 - 0.5 1 1 0.7 Dy 2.5 2.6 - 5.5 6.6 7 7.6 Ho 0.25 0.5 - 1 1 1 1.1 Er 1 1.7 - 3 3.8 3.5 3.3 Tm 0.5 0.2 - 0.5 0.5 0.5 0.5 Yb 1 1.3 - 3 2.9 2.9 2.9 Lu 0.25 0.2 - 0.25 0.5 0.5 0.4 Sc 35 - - 30 - - -Y 13 10 26 28 30 30 45Th 4 0.5 4 7 4.4 5.2 4.6 U 0.25 0.05 1 0.25 0.9 0.6 1.1 Zr 38 25 65 230 210 240 240Hf 2.5 2 - 5 10 8 10Nb 4 1 3 8 10 11 12Rb 2 4 2 74 75 80 80Ba 195 195 370 960 1300 930 1000Sr 210 310 340 210 320 300 300Cs 1.5 0.2 - 1.5 1.2 1.2 1.5 V 270 230 - 270 155 155 65Ta - 4 - - 4 2 4Cr 820 130 - 40 55 60 6Mo 2 0.05 - 1 0.5 1 1.2 W - 2 - - 2 2 2Ni 175 200 - 68 40 35 6Cu 90 110 - 46 30 30 15Ag 0.5 0.4 - 0.5 0.4 0.4 0.4 Zn 84 70 - 97 95 95 95Ga 18 35 20 19 100 90 85Ge 1 1 - 1 1 1 1Sn 4 3 - 1 1 3 2Pb 2.5 4 0.5 10 16 16 16Bi 1.5 0.1 - 1.5 0.1 0.1 0.1
45
APPENDIX 2d - Rare earth element analyses of quartzite from AYERS ROCK (analyses in parts per million); Dean – Dean Quartzite; Winnall – Winnall beds; basement - basement quartzite (LPq)
Sample A92/1 A93/16 A93/56 A93/169 A93/304 A93/1202 A94/375 A94/765 A94/766 A94/979 O94/7
Unit basement Dean basement basement basement basement Dean Dean Dean Dean DeanUGR (GDA94) FS940311 FS847395 FS807390 FS859345 FS859237 FS825259 FS778345 FS692482 FS692503 FS720601 FS544810La 11.5 11.5 5.5 2.9 1.85 15.5 20 8 3.7 5.5 9.5 Ce 23 22.5 10 6 4.4 43 41 16 7.5 9 17.5 Pr 2.5 2.6 1.1 0.55 0.35 3.6 4.3 1.65 0.8 1.1 1.85 Nd 8.5 9.5 3.9 1.9 1.2 12.5 14.5 5.5 2.8 3.8 7Sm 1.75 1.9 0.74 0.41 0.22 2.2 2.3 0.88 0.57 0.71 1.1 Eu 0.38 0.3 0.09 0.42 0.12 0.35 0.55 0.17 0.08 0.11 0.17 Gd 1.35 0.95 0.5 0.35 0.2 1.6 1.75 0.6 0.4 0.3 0.5 Tb 0.19 0.08 0.07 0.05 0.03 0.2 0.25 0.06 0.05 0.03 0.05 Dy 1.15 0.33 0.43 0.29 0.24 1.1 1.7 0.31 0.2 0.13 0.24 Ho 0.2 0.06 0.08 0.06 0.05 0.16 0.35 0.05 0.03 0.03 0.05 Er 0.5 0.1 0.25 0.2 0.15 0.4 1.3 0.2 0.05 0.05 0.1 Tm 0.05 0.025 0.025 0.025 0.025 0.05 0.2 0.025 0.025 0.025 0.025 Yb 0.4 0.15 0.3 0.25 0.15 0.3 1.35 0.2 0.025 0.1 0.15 Lu 0.06 0.02 0.04 0.05 0.03 0.05 0.23 0.04 0.01 0.01 0.02 Th 6.5 4 3.2 1.65 1.85 8.5 20 8.5 1.3 4.6 2.5
Sample O94/31 O94/54 BJ92/122 MP94/504 MP94/505 A94/752 A94/765 A94/766 A94/853 A94/895 A94/940
Unit Winnall Winnall Dean basement basement Dean Dean Dean basement Dean DeanUGR (GDA94) FT817254 FT554128 GS137533 GS651291 GS595364 FS680465 FS692482 FS692503 FS666413 FS705467 FS731475La 4.2 9.5 12 3.8 3.7 12 8 3.7 1.45 11.5 8Ce 7.5 14.5 24.5 10.5 10.5 21.5 16 7.5 1.95 23.5 17.5 Pr 0.85 1.65 2.7 0.8 0.8 2.6 1.65 0.8 0.15 2.2 1.8 Nd 3 6 9.5 3 2.7 10 5.5 2.8 0.41 8 6.5 Sm 0.51 1 2.1 0.51 0.58 1.65 0.88 0.57 0.04 1.6 1.2 Eu 0.08 0.16 0.33 0.13 0.14 0.21 0.17 0.08 0.01 0.31 0.23 Gd 0.35 0.55 1.1 0.35 0.45 0.7 0.6 0.4 0.025 1.05 0.8 Tb 0.05 0.06 0.1 0.04 0.06 0.05 0.06 0.05 0.01 0.11 0.08 Dy 0.29 0.33 0.44 0.19 0.39 0.25 0.31 0.2 0.02 0.5 0.35 Ho 0.05 0.06 0.08 0.03 0.07 0.05 0.05 0.03 0.01 0.09 0.06 Er 0.15 0.15 0.15 0.1 0.2 0.15 0.2 0.05 0.025 0.2 0.2 Tm 0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.025 Yb 0.15 0.2 0.2 0.1 0.2 0.15 0.2 0.025 0.025 0.2 0.2 Lu 0.02 0.03 0.03 0.02 0.03 0.03 0.04 0.01 0.01 0.03 0.03 Th 1.25 1.8 4 1.65 1.85 6 8.5 1.3 0.09 8.5 2.6
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APPENDIX 2e - Samarium-Neodymium and Rubidium-Strontium analyses of selected samples from AYERS ROCK; Model Age DM - model age with respect to a depleted mantle reservoir; e Nd(CHUR, T) - initial epsilon Nd at time of formation; 143Nd/144Nd (T) - initial Nd isotope condition at time of formation; 87Rb/86Sr (T) - initial Sr isotope condition at time of forma-tion; Kulpitjata - Kulpitjata Granite Complex; Allanah – Allanah Gneiss; Granulite gneiss - felsic granulite gneiss (LPfg) from Fregon subdomain
Sample A92/10A A93/63 A94/644 BJ96/277A BJ96/280 MP43
Lithology Kulpitjata Allanah Kulpitjata Kulpitjata Granulitegneiss
Allanah
Easting (GDA94) 689157 679427 674967 737627 740777 781900 Northing (GDA94) 7138695 7138215 7153615 7161665 7156365 7122400
Nd (ppm) 100.84 38.6 139.49 202.96 39.89 43.85 Sm (ppm) 18.06 7.19 18.78 35.32 7.98 7.6 143Nd/ 144Nd 0.511936 0.511830 0.511689 0.511822 0.511879 0.511761
± 0.000025 0.000025 0.000025 0.000025 0.000025 0.000025
Sm/Nd 0.1791 0.1863 0.1346 0.1740 0.2001 0.1733 147Sm/ 144Nd 0.1083 0.1127 0.0814 0.1053 0.1210 0.1048 143Nd/ 144Nd 0.512638 0.512638 0.512638 0.512638 0.512638 0.512638 143Nd/ 144Nd 0.513108 0.513108 0.513108 0.513108 0.513108 0.513108
Model Age CHUR 1.21 1.46 1.25 1.36 1.53 1.45 Model Age DM 1.66 1.89 1.61 1.77 1.97 1.85
Nd(0) -13.69 -15.76 -18.51 -15.92 -14.81 -17.11 Age (T, Ga) 1.148 1.539 1.190 1.166 1.135 1.554 143Nd/ 144Nd (T) 0.511120 0.510690 0.511053 0.511016 0.510977 0.510690 143Nd/ 144Nd (CHUR, T) 0.511156 0.510648 0.511101 0.511132 0.511172 0.510629
Nd (CHUR, T) -0.71 0.82 -0.95 -2.27 -3.82 1.2
87Sr/86Sr 0.801946 0.815188 0.780731 0.781166 0.758006 0.799467 ± 0.00005 0.00005 0.00005 0.00005 0.00005 0.00005
Sr (ppm) 123.08 117.78 194.55 191.13 174.92 150.29 Rb (ppm) 238.41 201.82 289.86 286.68 138.69 216.25 Rb/Sr 1.937 1.714 1.490 1.500 0.793 1.439 frac 87 1.222 1.223 1.219 1.219 1.217 1.222 atomic weight Sr 87 87.610 87.609 87.612 87.612 87.613 87.611 87Rb/ 86Sr 5.656 5.010 4.341 4.371 2.305 4.200 87Rb/ 86Sr (T) 0.708989 0.704499 0.706746 0.708195 0.720551 0.705747