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Intraplate magmatism Intraplate magmatism

Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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Page 1: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Intraplate magmatismIntraplate magmatism

Page 2: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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…)

Page 3: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Ocean islands and seamountsOcean islands and seamounts

Commonly associated with Commonly associated with hot spotshot spots

Figure 14-1. After Crough (1983) Ann. Rev. Earth Planet. Sci., 11, 165-193.

Page 4: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Oceanic islandsOceanic islands

Page 5: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

HotspotsHotspots

Page 6: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Mantle convection and mantle Mantle convection and mantle plumesplumes

Page 7: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Types of OIB MagmasTypes of OIB MagmasTwo principal magma seriesTwo principal magma series

TholeiiticTholeiitic series (dominant type) series (dominant type) Parental ocean island tholeiitic basalt, or Parental ocean island tholeiitic basalt, or OITOIT Similar to MORB, but some distinct chemical Similar to MORB, but some distinct chemical

and mineralogical differencesand mineralogical differences AlkalineAlkaline series (subordinate) series (subordinate)

Parental ocean island alkaline basalt, or Parental ocean island alkaline basalt, or OIAOIA Two principal alkaline sub-seriesTwo principal alkaline sub-series

silica undersaturatedsilica undersaturated slightly silica oversaturatedslightly silica oversaturated ( (less common less common

series) series)

Page 8: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Hawaiian ScenarioHawaiian ScenarioCyclic, pattern to the eruptive historyCyclic, pattern to the eruptive history

1. Pre-shield-building stage1. Pre-shield-building stage somewhat somewhat alkaline and variablealkaline and variable

2. Shield-building stage 2. Shield-building stage begins with begins with tremendous outpourings of tremendous outpourings of tholeiitic tholeiitic basaltsbasalts

Page 9: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Hawaiian ScenarioHawaiian Scenario3.3. Waning activity more Waning activity more alkalinealkaline, episodic, and , episodic, and

violent (Mauna Kea, Hualalai, and Kohala). violent (Mauna Kea, Hualalai, and Kohala). Lavas are also more diverse, with a larger Lavas are also more diverse, with a larger proportion of differentiated liquidsproportion of differentiated liquids

4.4. A long period of dormancy, followed by a A long period of dormancy, followed by a late, late, post-erosional stagepost-erosional stage. Characterized by . Characterized by highly alkalinehighly alkaline and silica-undersaturated and silica-undersaturated magmas, including alkali basalts, nephelinites, magmas, including alkali basalts, nephelinites, melilite basalts, and basanitesmelilite basalts, and basanites

Page 10: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Evolution in the SeriesEvolution in the SeriesTholeiitic, alkaline, and highly alkalineTholeiitic, alkaline, and highly alkaline

Figure 14-2. After Wilson (1989) Igneous Petrogenesis. Kluwer.

Page 11: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Trace ElementsTrace Elements The The LILLIL trace elements (K, Rb, Cs, Ba, Pb trace elements (K, Rb, Cs, Ba, Pb2+2+ and Sr) and Sr)

are incompatible and are are incompatible and are all enriched in OIB magmasall enriched in OIB magmas with respect to MORBswith respect to MORBs

The The ratiosratios of incompatible elements have been of incompatible elements have been employed to distinguish between source reservoirs employed to distinguish between source reservoirs N-MORB: the K/Ba ratio is high (usually > 100)N-MORB: the K/Ba ratio is high (usually > 100) E-MORB: the K/Ba ratio is in the mid 30’sE-MORB: the K/Ba ratio is in the mid 30’s OITs range from 25-40, and OIAs in the upper 20’sOITs range from 25-40, and OIAs in the upper 20’s

Thus all appear to have distinctive sourcesThus all appear to have distinctive sources

Page 12: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Trace ElementsTrace Elements HFSHFS elements (Th, U, Ce, Zr, Hf, Nb, Ta, and Ti) are also elements (Th, U, Ce, Zr, Hf, Nb, Ta, and Ti) are also

incompatible, and are enriched in OIBs > MORBsincompatible, and are enriched in OIBs > MORBs Ratios of these elements are also used to distinguish Ratios of these elements are also used to distinguish

mantle sourcesmantle sources The Zr/Nb ratioThe Zr/Nb ratio

N-MORBN-MORB generally quite high (>30)generally quite high (>30) OIBs are low (<10)OIBs are low (<10)

Page 13: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Trace Elements: REEsTrace Elements: REEs

Figure 14-2. After Wilson (1989) Igneous Petrogenesis. Kluwer.

Page 14: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

MORB-normalized Spider DiagramsMORB-normalized Spider Diagrams

Figure 14-3. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Sun and McDonough (1989).

Page 15: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Generation of tholeiitic and Generation of tholeiitic and alkaline basalts from a alkaline basalts from a chemicallychemically

uniformuniform mantle mantle

Figure 10-2 Figure 10-2 After After Wyllie, P. J. (1981). Geol. Wyllie, P. J. (1981). Geol. Rundsch. Rundsch. 7070, 128-153., 128-153.

Page 16: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Pressure effects:Pressure effects:

Figure 10-8 Figure 10-8 After Kushiro (1968), After Kushiro (1968), J. Geophys. Res.J. Geophys. Res., , 7373, 619-634., 619-634.

NeNe

FoFo EnEn

AbAb

SiOSiO22

Oversaturated(quartz-bearing)tholeiitic basalts

Highly undesaturated

(nepheline - b

earing)

alkali basalts

Undersaturated

tholeiitic basalts

EE3GPa3GPa

EE 2Gpa2Gpa

EE1GPa1GPa

EE 1atm1atm

Volatile-freeVolatile-free

Page 17: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Tholeiites favored by shallower meltingTholeiites favored by shallower melting 25% melting at 25% melting at <<30 km 30 km tholeiite tholeiite 25% melting at 60 km 25% melting at 60 km olivine basalt olivine basalt

Tholeiites favored by greater % partial meltingTholeiites favored by greater % partial melting 20 % melting at 60 km 20 % melting at 60 km alkaline basalt alkaline basalt

incompatibles (alkalis) incompatibles (alkalis) initial melts initial melts 30 % melting at 60 km 30 % melting at 60 km tholeiite tholeiite

Page 18: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Isotope GeochemistryIsotope Geochemistry Isotopes do not fractionate during partial Isotopes do not fractionate during partial

melting of fractional melting processes, so melting of fractional melting processes, so will reflect the characteristics of the sourcewill reflect the characteristics of the source

OIBs, which sample a great expanse of OIBs, which sample a great expanse of oceanic mantle in places where crustal oceanic mantle in places where crustal contamination is minimal, provide contamination is minimal, provide incomparable evidence as to the nature of incomparable evidence as to the nature of the mantlethe mantle

Page 19: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Simple Mixing ModelsSimple Mixing ModelsBinaryBinary

All analyses fall All analyses fall between two reservoirs between two reservoirs

as magmas mixas magmas mix

TernaryTernaryAll analyses fall within All analyses fall within

triangle determined triangle determined by three reservoirsby three reservoirs

Figure 14-5. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Page 20: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Figure 14-6. After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).

Page 21: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Mantle ReservoirsMantle Reservoirs1.1. DMDM (Depleted Mantle) = N-MORB source (Depleted Mantle) = N-MORB source

Figure 14-6. After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).

Page 22: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

2.2. BSEBSE (Bulk Silicate Earth) or the Primary (Bulk Silicate Earth) or the Primary Uniform ReservoirUniform Reservoir

Figure 14-6. After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).

Page 23: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

3.3. EMIEMI = enriched mantle type I has lower = enriched mantle type I has lower 8787Sr/Sr/8686Sr (near Sr (near primordial) primordial)

4.4. EMIIEMII = enriched mantle type II has higher = enriched mantle type II has higher 8787Sr/Sr/8686Sr (> Sr (> 0.720, well above any reasonable mantle sources0.720, well above any reasonable mantle sources

Figure 14-6. After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).

Page 24: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

5.5. PREMAPREMA ( (PREPREvalent valent MAMAntle)ntle)

Figure 14-6. After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).

Page 25: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Figure 14-6. After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al. (1986) and Wilson (1989).

Page 26: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Pb IsotopesPb Isotopes Pb produced by radioactive decay of U & ThPb produced by radioactive decay of U & Th

238238U U 234234U U 206206PbPb235235U U 207207PbPb232232Th Th 208208PbPb

Pb isotopes also characterize the different Pb isotopes also characterize the different reservoirs (see paper presentation Hart 1984)reservoirs (see paper presentation Hart 1984)

Page 27: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Figure 14-8. After Wilson (1989) Igneous Petrogenesis. Kluwer. Data from Hamelin and Allègre (1985), Hart (1984), Vidal et al. (1984).

Page 28: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Kellogg et al. (1999)

Page 29: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

A Model for Oceanic MagmatismA Model for Oceanic Magmatism

DMDM

OIBOIB

ContinentalContinental

ReservoirsReservoirs

EM and HIMU from EM and HIMU from crustalcrustal sources (subducted OC + CC seds) sources (subducted OC + CC seds)

Figure 14-10. Nomenclature from Zindler and Hart (1986). After Wilson (1989) and Rollinson (1993).

Page 30: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

““Marble cake” model for mantle convection & mixingMarble cake” model for mantle convection & mixing

Page 31: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Continental Flood BasaltsContinental Flood Basalts

Large Igneous Provinces (LIPs)Large Igneous Provinces (LIPs) Oceanic plateausOceanic plateaus Some riftsSome rifts Continental flood basalts Continental flood basalts

(CFBs)(CFBs)

Figure 15-1. Columbia River Basalts at Hat Point, Snake River area. Cover of Geol. Soc. Amer Special Paper 239. Photo courtesy Steve Reidel.

Table 15-1. Major Flood Basalt Provinces

Name Volume Age Locality

CRB (1.7x105 km3) Miocene NW US

Keeweenawan (4x105 km3) Precambrian Superior area

Deccan (106 km3) Cret.-Eocene India

Parana (area > 106 km2) early Cret. Brazil

Karroo (2x106 km3?) early Jurassic S. Africa

Page 32: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Trapp volcanismTrapp volcanism

Page 33: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

LIPs (Large Igneous Provinces)LIPs (Large Igneous Provinces)

Page 34: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB
Page 35: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

CFB’sCFB’s

Associated to major continental break-upAssociated to major continental break-up … … or/and to plume head impactor/and to plume head impact

Page 36: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB
Page 37: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Figure 15-2. Flood basalt provinces of Gondwanaland prior to break-up and separation. After Cox (1978) Nature, 274, 47-49.

Page 38: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Figure 15-3. Relationship of the Etendeka and Paraná plateau provinces to the Tristan hot spot. After Wilson (1989), Igneous Petrogenesis. Kluwer.

Page 39: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

GeochemistryGeochemistry

Deccan traps basaltsDeccan traps basalts

Page 40: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Bimodal magmasBimodal magmas

Basalts and rhyolitesBasalts and rhyolites Secondary melting?Secondary melting? Effect of the two eutectics?Effect of the two eutectics?

Page 41: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Figure 15-7. Condrite-normalized rare earth element patterns of some typical CRBG samples. Winter (2001). An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Hooper and Hawkesworth (1993) J. Petrol., 34, 1203-1246.

Page 42: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Figure 15-13. A model for the origin of the Columbia River Basalt Group From Takahahshi et al. (1998) Earth Planet. Sci. Lett., 162, 63-80.

Page 43: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

LIPs and mass extinctionsLIPs and mass extinctions

Page 44: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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

Page 45: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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…)

Page 46: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Common features of continental Common features of continental alkali seriesalkali series

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

Page 47: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

Alkaline seriesAlkaline series

Strongly alkalineStrongly alkalineMildly alkalineMildly alkaline

Page 48: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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.

Page 49: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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.

Page 50: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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.

Page 51: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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.

Page 52: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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.

Page 53: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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!

Page 54: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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.

Page 55: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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.

Page 56: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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

Page 57: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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

Page 58: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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

Page 59: Intraplate magmatism. l Hotspots l Rift zones (often associated with hotspots) l Intra-oceanic plate: Tholeitic to alkaline series; mostly basalts (OIB

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.

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Bimodal associations againBimodal associations again(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?

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The oddities…The oddities…

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

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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

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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.

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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

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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

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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, …)Wyomingite, …)

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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

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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

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Figure 19-17. Chondrite-normalized rare earth element diagram showing the range of patterns for olivine-, phlogopite-, and madupitic-lamproites from 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: Chapter 19: Continental Continental

Alkaline Alkaline Magmatism.Magmatism.Lamproites Lamproites

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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

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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

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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