lithospheric pmd crc geodynamics: a seismic view of the ...lithospheric pmd crc geodynamics: a...

‘‘Reduced Discovery Risk through Improved TargetingReduced Discovery Risk through Improved Targeting’’

pmd CRCLithosphericGeodynamics: a seismicview of the Yilgarn Craton

The Y2 project (2001-2004)The Y2 project (2001-2004)

pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery

OutlineOutline

Seismic (general sense) signature of:

• subduction and slabs

• mantle plumes

• delamination and possiblegeneration of Low-Ca granites

• Provinciality/terranes

• Conclusions


Subduction and tomographySubduction and tomography

• Yilgarn subduction atvarious times(geochemistry)

• Both east- and west-dipping slabs

• Can we see the‘signature’ ofsubduction?

• Slabs characterised byfast S-wave velocities

Tomography of slabs under Japan (Fukao et al. 2001)

velocity


YouanmiYouanmi

KalgoorlieKalgoorlieN

?

?

Felsicvolcanism

2760-2730 MaYoung east?

Felsicvolcanism?

2740-2730 MaZircon

inheritance

SE-dipping subduction zones?SE-dipping subduction zones?

Cassidy & Champion (2004)

Postulated SE-dipping slab ca 2.76-2.73 Ga


Mafic/calc-alkaline

High-Ca

High-HFSE

Fault

Co

nti

nen

tal

cru

st

Oce

anic

cru

st

Slab

EAST

Mantle upwelling produceskomatiites

Together?

Kalgoorlie Terrane Kurnalpi Terrane

Ca 2.705 Ga

Morris & Witt (1997)

Models for West-dipping subductionat ~2.7 Ga

Champion & Cassidy (2001)

W-dipping subduction zones?W-dipping subduction zones?


EEGPY (SC)M

120km

350 km

W

500 km

Ida F Yamarna F

Stratified lithosphere as a slab?Stratified lithosphere as a slab?


EEGPY (SC)M

120km

350 km

W

500 km

• SE-dipping (low-angle) fast layer (4.8 km/s)

Ida F Yamarna F



EEGPY (SC)M

120km

350 km

W

500 km

• SE-dipping (low-angle) fast layer (4.8 km/s)• possibly a fossil slab (cf. Narryer at 2.75Ga)

Ida F Yamarna F



EEGPY (SC)M

120km

350 km

W

500 km


• no evidence for the W-dipping 2.7 Ga slab?

Ida F Yamarna F



EEGPY (SC)M

120km

350 km

W

500 km



Ida F Yamarna F


• The age of the high-velocity layer is unknown


EEGPY (SC)M

120km

350 km

W

500 km



Ida F Yamarna F


We can not rule slabs in or out on this evidence

• The age of the high-velocity layer is unknown


Gutscher et al. (2000)

EEGPY (SC)M

120km

350 km

W

500 km

500 km

Ida F Yamarna F

Chilean analogue for flat subductionChilean analogue for flat subduction


Bijwaard et al. (2004)

Mantle plumes and tomographyMantle plumes and tomography

Iceland plume tomography

Modern mantleplumes are:




• large (several100’s to 1000’skms in diameter)







• Originate from thevery deep earth







• Originate from thevery deep earth

• Have low P- and S-wave velocities




Plume Morris & Witt (1997)

Mafic/calc-alkaline

High-Ca

High-HFSE

Fault

Co

ntin

enta

lcr

ust

Oce

anic

cru

st

Slab

EAST

Mantle upwelling produceskomatiites

Together?

Kalgoorlie Terrane Kurnalpi Terrane

Ca 2.705 Ga

Champion & Cassidy (2001)

Plumes havebeenhypothesisedfor komatiites(eg Morris & Witt, 1997;

Champion etc),

and manygranites (egCampbell & Hill, 1988 andlater papers)

Yilgarn mantle plumes?Yilgarn mantle plumes?


350 km

EEGPY (SC)M

500 km

120 km

Ida F Yamarna F

Impingement of a mantle plume?Impingement of a mantle plume?W


350 km

EEGPY (SC)M

500 km

• If a high-level plume: it would disrupt this stratification(assuming stratification is old)

120 km

Ida F Yamarna F



350 km

EEGPY (SC)M

500 km


• Or, horizontal reworking was dominant after the plume

120 km

Ida F Yamarna F



350 km

EEGPY (SC)M

500 km


• Or, horizontal reworking was dominant after the plume• Or, disruption is out of this plane

120 km

Ida F Yamarna F



350 km

EEGPY (SC)M

500 km


• Or, horizontal reworking was dominant after the plume• Or, disruption is out of this plane• If a deep plume we wouldn’t see it in this section

120 km

Ida F Yamarna F



350 km

EEGPY (SC)M

500 km


• Or, horizontal reworking was dominant after the plume• Or, disruption is out of this plane• If a deep plume we wouldn’t see it in this section

120 km

We can not rule plumes in or out on this evidence

Ida F Yamarna F



• Major types(Low-Ca, High-Ca)

• Crustal melts

• Intrudeexternalgranites (atbase ofgreenstone)

• Late <2655 MaLow-Ca granite greenstone

Champion & Sheraton (1997)

Yilgarn delamination?Yilgarn delamination?


500 km

AMIRA P624; Blewett et al., 2004

Delamination:

Ida F Yamarna F

Fast layer as delaminated Fast layer as delaminated ‘‘restiterestite’’??

Restite layer??

350 km

120 km

EEGPY (SC)MW


500 km

• delivers heat across entire Yilgarn (Low-Ca arecraton-wide)


Delamination:

Ida F Yamarna F


Restite layer??

350 km

120 km

EEGPY (SC)MW


500 km


• Initiated at ~2670 Ma (first D2a event in east)


Delamination:

Ida F Yamarna F


Restite layer??

350 km

120 km

EEGPY (SC)MW


500 km


• Initiated at ~2670 Ma (first D2a event in east)• Low-Ca granites ~2655 Ma (E) to 2640 (W)


Delamination:

Ida F Yamarna F


Restite layer??

350 km

120 km

EEGPY (SC)MW


500 km


• Initiated at ~2670 Ma (first D2a event in east)• Low-Ca granites ~2655 Ma (E) to 2640 (W)• Synchronous with Au ages?


Delamination:

Ida F Yamarna F


Restite layer??

350 km

120 km

EEGPY (SC)MW


500 km




DelaminationDelaminationDelaminationDelamination

Delamination:

Ida F Yamarna F


Restite layer??

350 km

120 km

EEGPY (SC)MW


500 km





Heat?Heat?

Delamination:

Ida F Yamarna F


Restite layer??

350 km

120 km

EEGPY (SC)MW


500 km





Heat?Heat?

Delamination:

meltIda F Yamarna F


Restite layer??

350 km

120 km

EEGPY (SC)MW


• Intrude externalgranites (base ofgreenstone)

• Relatively lowdensity,relatively slow(seismically)

Terranes of the Yilgarn Craton:the Low-Ca granites

Terranes of the Yilgarn Craton:Terranes of the Yilgarn Craton:the Low-Ca granitesthe Low-Ca granites

Low-Ca granite greenstone

Ida

Fau

lt


• Intrude externalgranites (base ofgreenstone)

• Relatively lowdensity,relatively slow(seismically)

Terranes of the Yilgarn Craton:the Low-Ca granites

Terranes of the Yilgarn Craton:Terranes of the Yilgarn Craton:the Low-Ca granitesthe Low-Ca granites

Low-Ca granite greenstone

Ida

Fau

ltNext 2 slides


Youanmi Kalgoorlie

S-wave velocity increase

dept

h

E• Kalgoorlie has

low-velocitylayer at ~10 km= less density

• Not simplyreflectingoverlyinggreenstones

Moho

Terranes of the Yilgarn Craton:upper crust from receiver functions

Terranes of the Yilgarn Craton:Terranes of the Yilgarn Craton:upper crust from receiver functionsupper crust from receiver functions

Kurnalpi

10 km

Australian average velocity profile

Calculated crustal velocity profile


Youanmi Kalgoorlie

S-wave velocity increase

dept

h

E

World average crustal velocity profile

Calculated crustal velocity profile

Moho

Terranes of the Yilgarn Craton:upper crust from receiver functions

Terranes of the Yilgarn Craton:Terranes of the Yilgarn Craton:upper crust from receiver functionsupper crust from receiver functions

• Thick Low-Cagranite‘underplate’under Kal fromcrustal anatexis(link to Au)

• Thick Low-Casignature of Kalendowment??

Kurnalpi

Crustal melts


Jon Hronsky(WMC)

Lots of arm waving isLots of arm waving isinteresting, but how does it helpinteresting, but how does it help

us?us?Better

understanding ofthe minerals system

process –geodynamics is anintegral component

and driver of themass and energy

flux


ConclusionsConclusions

• ‘Signatures’ of the mass and energy fluxat the largest scale are visible in variousseismic methods (tomography, receiverfunctions)

• We don’t always understand the‘signatures’

• a complex mantle lithosphere and crust,especially the temporal component

• Geodynamic implications for slabs,plumes and delamination; tectonicdevelopment in general


Predictive Mineral DiscoveryPredictive Mineral Discovery

• Yilgarn is data-rich and we need abetter methodology (paradigm?) tounderstand the ‘signatures’

• The way forward is clearly a holisticsystems approach across alllithospheric scales and dimensions

• Need to integrate in 3D with time

• Erect multiple hypotheses and applysuitable tests


Challenge for us allChallenge for us all

• Challenge is being predictive with thisnew understanding and knowledge

• The system may be recognised eventhough the precise genetic links withmineralisation are unclear (Hronsky,2004),


Challenge for us allChallenge for us all

• Challenge is being predictive with thisnew understanding and knowledge

• The system may be recognised eventhough the precise genetic links withmineralisation are unclear (Hronsky,2004),

but we are working hard on itbut we are working hard on it(pmd*(pmd*CRC Y-New project)CRC Y-New project)


Thanks for listening

lithospheric pmd crc geodynamics: a seismic view of the ...lithospheric pmd crc geodynamics: a...

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