Intraplate magmatismIntraplate magmatism HotspotsHotspots Rift zones (often associated with hotspots)Rift zones (often associated with hotspots)

Intra-oceanicIntra-oceanic plate: Tholeitic to alkaline series; mostly plate: Tholeitic to alkaline series; mostly basalts (basalts (OIBOIB = Oceanic Islands Basalts), some = Oceanic Islands Basalts), some differenciated alkaline termsdifferenciated alkaline terms

Intra-continentalIntra-continental plate: plate: either large tholeitic basaltic provinces (either large tholeitic basaltic provinces (CFBCFB = Continental Flood = Continental Flood

Basalts), occasionally bimodal (ass. with Basalts), occasionally bimodal (ass. with rhyolitesrhyolites)) or smaller, or smaller, alkaline to hyper-alkalinealkaline to hyper-alkaline, differenciated , differenciated

intrusions/volcanoes (syenites/phonolites; carbonatites; intrusions/volcanoes (syenites/phonolites; carbonatites; kimberlites; and more…)kimberlites; and more…)

Continental alkaline seriesContinental alkaline series

Alkali volcanoes – basaltic strombolian cone in front,Alkali volcanoes – basaltic strombolian cone in front,trachytic pelean dome behind– in the West European rift trachytic pelean dome behind– in the West European rift

The West-The West-european rift european rift

sytemsytem

Continental Alkaline Continental Alkaline Magmatism.Magmatism.

The East African Rift The East African Rift

Figure 19-2. Map of the East African Rift system (after Kampunzu and Mohr, 1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp. 85-136. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Continental alkaline seriesContinental alkaline series

Rift (or hotspot) relatedRift (or hotspot) related Large diversity (possibly > 80% of the rock Large diversity (possibly > 80% of the rock

names, for <1% volume !)names, for <1% volume !) Strange rocks (carbonatites…)Strange rocks (carbonatites…)

Common features of continental Common features of continental alkali seriesalkali series

Alkaline (!)Alkaline (!) Undersaturated to just oversaturatedUndersaturated to just oversaturated PeralkalinePeralkaline

Alkaline seriesAlkaline series

Strongly alkalineStrongly alkalineMildly alkalineMildly alkaline

Quartz-richGranitoid

9090

6060

2020Alkali Fs.Quartz Syenite Quartz

SyeniteQuartz

MonzoniteQuartz

Monzodiorite

Syenite Monzonite Monzodiorite

(Foid)-bearingSyenite

5

10 35 65

(Foid)-bearingMonzonite

(Foid)-bearingMonzodiorite

90

Alkali Fs.Syenite

(Foid)-bearingAlkali Fs. Syenite

10

(Foid)Monzosyenite

(Foid) Syenite

(Foid)Monzodiorite

(Foi

d) G

abbr

o

Qtz. Diorite/Qtz. Gabbro

5

10

Diorite/Gabbro/Anorthosite

(Foid)-bearingDiorite/Gabbro

60

(Foid)olites

Quartzolite

Granite Grano-diorite

Tonalite

Alka

li Feld

spar

Gra

nite

Q

A P

F

60

(foid)-bearing Trachyte

(foid)-bearing Latite

(foid)-bearing Andesite/Basalt

(Foid)ites

10

60 60

35 65

10

20 20

60 60

F

A P

Q

Rhyolite Dacite

Trachyte Latite Andesite/Basalt

Phonolite Tephrite

SaturatedSaturated

Under-saturatedUnder-saturated

The alkali eutecticThe alkali eutectic

Figure 19-7. Phase diagram for the system SiO2-NaAlSiO4-KAlSiO4-H2O at 1 atm. pressure. Insert shows a T-X section from the silica-

undersaturated thermal minimum (Mu) to the silica-oversaturated thermal minimum (Ms). that crosses the lowest point (M) on the

binary Ab-Or thermal barrier that separates the undersaturated and oversaturated zones. After Schairer and Bowen (1935) Trans. Amer. Geophys. Union, 16th Ann. Meeting, and Schairer (1950), J. Geol., 58, 512-517. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Al2O3K2O

CaO

Al2O3

K2O

CaO

Al2O3

CaO

biotitemuscovitecordieriteandalusitegarnet

pyroxenehornblendebiotite

aegirineriebeckitearfvedsonite

Peraluminous Metaluminous Peralkaline

mol

es

Na2ONa2O

K2O

Na2O

CaO

Figure 18-2. Alumina saturation classes based on the molar proportions of Al2O3/(CaO+Na2O+K2O) (“A/CNK”) after

Shand (1927). Common non-quartzo-feldspathic minerals for each type are included. After Clarke (1992). Granitoid Rocks. Chapman Hall.

Trace elements enrichedTrace elements enriched

Figure 19-5. Chondrite-normalized REE variation diagram for examples of the four magmatic series of the East African Rift (after Kampunzu and Mohr, 1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp. 85-136. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Enriched mantle sourceEnriched mantle source

Figure 19-3. 143Nd/144Nd vs. 87Sr/86Sr for East African Rift lavas (solid outline) and xenoliths (dashed). The “cross-hair” intersects at Bulk Earth (after Kampunzu and Mohr, 1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp. 85-136. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Generated from low to very low melt fractionsGenerated from low to very low melt fractions

Figure 19-14. Grid showing the melting products as a function of pressure and % partial melting of model pyrolite mantle with 0.1% H2O. Dashed curves are the stability limits of the minerals indicated. After Green (1970), Phys. Earth Planet. Inter., 3, 221-235. Winter

(2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Diversity of alkaline continental Diversity of alkaline continental magmas – some examplesmagmas – some examples

Saturated alkaline seriesSaturated alkaline series Undersaturated alkaline seriesUndersaturated alkaline series

CarbonatitesCarbonatites Lamprophyres, kimberlites & co.Lamprophyres, kimberlites & co.

Series with a true Series with a true geological geological importanceimportance

Oddities and Oddities and curiosities – but curiosities – but economic economic importance!importance!

Figure 19-1. Variations in alkali ratios (wt. %) for oceanic (a) and continental (b) alkaline series. The heavy dashed lines distinguish the alkaline magma subdivisions from Figure 8-14 and the shaded area represents the range for the more common oceanic intraplate series. After McBirney (1993). Igneous Petrology (2nd ed.), Jones and Bartlett. Boston. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Continental Alkaline Continental Alkaline Magmatism.Magmatism.

The East African Rift The East African Rift

Figure 19-2. Map of the East African Rift system (after Kampunzu and Mohr, 1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp. 85-136. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

East African rift (Afar) – mildly alkalineEast African rift (Afar) – mildly alkaline

0

2

4

6

8

10

12

14

16

38 43 48 53 58 63 68 73 78

SiO2

Na

2O

+K

2O

Central African Rift – Strongly alkalineCentral African Rift – Strongly alkaline

0

2

4

6

8

10

12

14

16

38 43 48 53 58 63 68 73 78

SiO2

Na

2O

+K

2O

Two main seriesTwo main series

Basalts-Trachydandesites-Trachydacites-Basalts-Trachydandesites-Trachydacites-Rhyolites (stronly bimodal): Rhyolites (stronly bimodal): (just) saturated (just) saturated alkali seriesalkali series A-type granites can be formed thereA-type granites can be formed there Role of the preexisting crust?Role of the preexisting crust?

Basanite-Foidite (nephelinite)-Phonolite: Basanite-Foidite (nephelinite)-Phonolite: strongly undersaturated alkali seriesstrongly undersaturated alkali series

Figure 19-9. Hypothetical cross sections (same vertical and horizontal scales) showing a proposed model for the progressive development of the East African Rift System. a. Pre-rift stage, in which an asthenospheric mantle diapir rises (forcefully or passively) into the lithosphere. Decompression melting (cross-hatch-green indicate areas undergoing partial melting) produces variably alkaline melts. Some partial melting of the metasomatized sub-continental lithospheric mantle (SCLM) may also occur. Reversed decollements (D1)

provide room for the diapir. b. Rift stage: development of continental rifting, eruption of alkaline magmas (red) mostly from a deep asthenospheric source. Rise of hot asthenosphere induces some crustal anatexis. Rift valleys accumulate volcanics and volcaniclastic material. c. Afar stage, in which asthenospheric ascent reaches crustal levels. This is transitional to the development of oceanic crust. Successively higher reversed decollements (D2 and D3)

accommodate space for the rising diapir. After Kampunzu and Mohr (1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp. 85-136 and P. Mohr (personal communication). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Bimodal associationsBimodal associations(the « Daly gap »)(the « Daly gap »)

Mantle vs. Crustal sources?Mantle vs. Crustal sources? Remelting of underplated basalts?Remelting of underplated basalts? Simply an effect of the different eutectics?Simply an effect of the different eutectics?

0

2

4

6

8

10

12

14

16

38 43 48 53 58 63 68 73 78

SiO2

Na

2O

+K

2O

The oddities…The oddities…

CarbonatitesCarbonatites Lamproites, kimberlites, etc.Lamproites, kimberlites, etc.

Chapter 19: Continental Chapter 19: Continental Alkaline Magmatism.Alkaline Magmatism.

Carbonatites Carbonatites

Calcite- Dolomite- Ferro- Natro-% carbonatite carbonatite carbonatite carbonatite

SiO2 2.72 3.63 4.7 0.16

TIO2 0.15 0.33 0.42 0.02

Al2O3 1.06 0.99 1.46 0.01

Fe2O3 2.25 2.41 7.44 0.05

FeO 1.01 3.93 5.28 0.23 MnO 0.52 0.96 1.65 0.38 MgO 1.80 15.06 6.05 0.38 CaO 49.1 30.1 32.8 14.0

Na2O 0.29 0.29 0.39 32.2

K2O 0.26 0.28 0.39 8.38

P2O5 2.10 1.90 1.97 0.85

H2O+ 0.76 1.20 1.25 0.56

CO2 36.6 36.8 30.7 31.6

BaO 0.34 0.64 3.25 1.66 SrO 0.86 0.69 0.88 1.42 F 0.29 0.31 0.45 2.50 Cl 0.08 0.07 0.02 3.40 S 0.41 0.35 0.96

SO3 0.88 1.08 4.14 3.72

Table 19-5. Representative Carbonatite Compositions

Calcite- Dolomite- Ferro- Natro-% carbonatite carbonatite carbonatite carbonatiteppmLi 0.1 - 10 -Be 2 < 5 12 -Sc 7 14 10 -V 80 89 191 116Cr 13 55 62 0Co 11 17 26 -Ni 18 33 26 0Cu 24 27 16 -Zn 188 251 606 88Ga < 5 5 12 <20Rb 14 31 - 178Y 119 61 204 7Zr 189 165 127 0Nb 1204 569* 1292 28Mo - 12 71 125Ag - 3 4 -Cs 20 1 1 6Hf - 3 - 0Ta 5 21 1 0W - 10 20 49Au - - 12 -Pb 56 89 217 -Th 52 93 276 4U 9 13 7 11La 608 764 2666 545Ce 1687 2183 5125 645Pr 219 560 550 -Nd 883 634 1618 102Sm 130 45 128 8Eu 39 12 34 2Gd 105 - 130 -Tb 9 5 16 -Dy 34 - 52 2Ho 6 - 6 -Er 4 - 17 -Tm 1 - 2 -Yb 5 10 16 -Lu 1 0 - 0Wooley & Kempe (1989), natrocarb. from Keller & Spettel (1995).

* one excluded analysis contained 16,780 ppm Nb.

Table 19-5. Representative Carbonatite Compositions

Carbonatites Carbonatites

Figure 19-11. Idealized cross section of a carbonatite-alkaline silicate complex with early ijolite cut by more evolved urtite. Carbonatite (most commonly calcitic) intrudes the silicate plutons, and is itself cut by later dikes or cone sheets of carbonatite and ferrocarbonatite. The last events in many complexes are late pods of Fe and REE-rich carbonatites. A fenite aureole surrounds the carbonatite phases and perhaps also the alkaline silicate magmas. After Le Bas (1987) Carbonatite magmas. Mineral. Mag., 44, 133-40. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Figure 19-15. Silicate-carbonate liquid immiscibility in the system Na2O-

CaO-SiO2-Al2O3-CO2 (modified by

Freestone and Hamilton, 1980, to incorporate K2O, MgO, FeO, and

TiO2). The system is projected from

CO2 for CO2-saturated conditions.

The dark shaded liquids enclose the miscibility gap of Kjarsgaard and Hamilton (1988, 1989) at 0.5 GPa, that extends to the alkali-free side (A-A). The lighter shaded liquids enclose the smaller gap (B) of Lee and Wyllie (1994) at 2.5 GPa. C-C is the revised gap of Kjarsgaard and Hamilton. Dashed tie-lines connect some of the conjugate silicate-carbonate liquid pairs found to coexist in the system. After Lee and Wyllie (1996) International Geology Review, 36, 797-819. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Chapter 19: Continental Alkaline Magmatism.Chapter 19: Continental Alkaline Magmatism.Carbonatites Carbonatites

Figure 19-15. Schematic cross section of an asthenospheric mantle plume beneath a continental rift environment, and the genesis of nephelinite-carbonatites and kimberlite-carbonatites. Numbers correspond to Figure 19-13. After Wyllie (1989, Origin of carbonatites: Evidence from phase equilibrium studies. In K. Bell (ed.), Carbonatites: Genesis and Evolution. Unwin Hyman, London. pp. 500-545) and Wyllie et al., (1990, Lithos, 26, 3-19). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Chapter 19: Continental Alkaline Magmatism.Chapter 19: Continental Alkaline Magmatism.Carbonatites Carbonatites

Lamproites and kimberlitesLamproites and kimberlites

… … many, many, many rock typesmany, many, many rock types … … many, many different names – mostly many, many different names – mostly

purely local and after the one known purely local and after the one known occurrence of that rock type occurrence of that rock type (Vosgesite, (Vosgesite, Wyomingite, Orangeite …)Wyomingite, Orangeite …)

Chapter 19: Chapter 19: Continental Alkaline Continental Alkaline

Magmatism.Magmatism.Kimberlites Kimberlites

Lamproite*

SiO2 33.0 27.8-37.5 35.0 27.6-41.9 45.5

TiO2 1.3 0.4-2.8 1.1 0.4-2.5 2.3

Al2O3 2.0 1.0-5.1 2.9 0.9-6.0 8.9

FeO* 7.6 5.9-12.2 7.1 4.6-9.3 6.0 MnO 0.14 0.1-0.17 0.19 0.1-0.6MgO 34.0 17.0-38.6 27. 10.4-39.8 11.2 CaO 6.7 2.1-21.3 7.5 2.9-24.5 11.8

Na2O 0.12 0.03-0.48 0.17 0.01-0.7 0.8

K2O 0.8 0.4-2.1 3.0 0.5-6.7 7.8

P2O5 1.3 0.5-1.9 1.0 0.1-3.3 2.1

LOI 10.9 7.4-13.9 11.7 5.2-21.5 3.5

Sc 14 20 19V 100 95 66Cr 893 1722 430Ni 965 1227 152Co 65 77 41Cu 93 28Zn 69 65Ba 885 3164 9831Sr 847 1263 3860Zr 263 268 1302Hf 5 7 42Nb 171 120 99Ta 12 9 6Th 20 28 37U 4 5 9La 150 186 297Yb 1 1 1Data from Mitchell (1995), Mitchell and Bergman (1991)

* Leucite Hills madupidic lamproite

Table 19-8. Average Analyses and Compositional Ranges of Kimberlites, Orangeites, and Lamproites.

Kimberlite Orangeite

Figure 19-18a. Initial 87Sr/86Sr vs. 143Nd/144Nd for lamproites (red-brown) and kimberlites (red). MORB and the Mantle Array are included for reference. After Mitchell and Bergman (1991) Petrology of Lamproites. Plenum. New York. Typical MORB and OIB from Figure 10-13 for comparison. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Chapter 19: Continental Alkaline Magmatism.Chapter 19: Continental Alkaline Magmatism.Lamproites Lamproites

Figure 19-20a. Chondrite-normalized REE diagram for kimberlites, unevolved orangeites, and phlogopite lamproites (with typical OIB and MORB). After Mitchell (1995) Kimberlites, Orangeites, and Related Rocks. Plenum. New York. and Mitchell and Bergman (1991) Petrology of Lamproites. Plenum. New York. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Chapter 19: Chapter 19: Continental Alkaline Continental Alkaline

Magmatism.Magmatism.Kimberlites Kimberlites

Figure 19-19. Model of an idealized kimberlite system, illustrating the hypabyssal dike-sill complex leading to a diatreme and tuff ring explosive crater. This model is not to scale, as the diatreme portion is expanded to illustrate it better. From Mitchell (1986) Kimberlites: Mineralogy, Geochemistry, and Petrology. Plenum. New York. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Chapter 19: Chapter 19: Continental Alkaline Continental Alkaline

Magmatism.Magmatism.Kimberlites Kimberlites

Figure 19-20b. Hypothetical cross section of an Archean craton with an extinct ancient mobile belt (once associated with subduction) and a young rift. The low cratonal geotherm causes the graphite-diamond transition to rise in the central portion. Lithospheric diamonds therefore occur only in the peridotites and eclogites of the deep cratonal root, where they are then incorporated by rising magmas (mostly kimberlitic- “K”). Lithospheric orangeites (“O”) and some lamproites (“L”) may also scavenge diamonds. Melilitites (“M”) are generated by more extensive partial melting of the asthenosphere. Depending on the depth of segregation they may contain diamonds. Nephelinites (“N”) and associated carbonatites develop from extensive partial melting at shallow depths in rift areas. After Mitchell (1995) Kimberlites, Orangeites, and Related Rocks. Plenum. New York. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Chapter 19: Continental Alkaline Magmatism.Chapter 19: Continental Alkaline Magmatism.Kimberlites Kimberlites