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Igneous petrology Part II – Important igneous associations • Granites (and convergence/collision) • Ophiolites (oceanic crust) and MORB (Mid-ocean ridge basalts) • Layered igneous complexes (intra-plate, economic importance) • Oceanic island basalts (OIB) (intraplate) • Continental alkali series (intraplate) • Andesites (active subductions) • Continental arcs (active subductions) • TTG (Archaean) • Komatiites (Archaean) Granites and collisions Exemple of the Himalaya • Granites are typically associated to convergent plate boundaries • Different types form at different moments of the convergence • Example of an active collision zone : the Himalaya Subducting oceanic lithosphere deforms sediment at edge of continental plate Collision – welding together of continental crust Post-collision: two continental plates are welded together, mountain stands where once was ocean Rifting of continental crust to form a new ocean basin The Himalayas: geodynamic context • India-Eurasia convergence • Destruction of the Tethys ocean • Subduction stage (> 100 Ma – 25 Ma = Cretaceous-Oligocene) • Collision stage (25 Ma – present = Miocene and Pliocene) • Post-collision stage (present) Himalayan collision 5 cm/an 10 cm/an 18 cm/an Remontée de l ’Inde et collision à 55 Ma C. 70 Ma 30° M ak ra n Asian Margin O m KohistanLadakh an F u tu Arabia 0° re IT SZ Tibet W S.L. F Fr u t u r ac e tu O w re e zo n ne Africa S.T. ? 30° India Intra-oceanic arc Active continental margin The subduction stage Les témoins de la subduction de l ’Inde sous l ’Asie Zanskar Indian crust MHT The Les témoins de la collisioncollision stagecontinentale Std Ky Bt Mu Zanskar Indian crust MHT 400 T°C 500 700 600 2 4 L 50 Ma M2 18-25 Ma 6 8 M1 10 45 Ma 37-32 Ma SSW NNE Spontang Tethys -Himalaya MHT Higher Himalaya Tibet Ladakh Moho 55 Ma N eo t eth Shikar Beh Higher Himalaya Tethys -Himalaya MHT Ladakh Tibet 50 Ma 55-40 Ma : > 400 km > 2.6 cm/y Sub-Himalaya Tethys -Himalaya Lesser Himalaya Ladakh Higher Himalaya MHT Tibet 40 Ma ISZ STDS MCT 0 Sub-Himalaya 30 60 km Less er H im Tethys -Himalaya alaya Tibet Moho MHT 0 30 60km 40-20 Ma : ~ 360 km , ~ 1.8 cm/y 20 Ma ys Erosion 200 400 600 200°C 10 400 20 600 30 800 40 50 km 800 0 100 200 km The « late to post » collision stage Successive magmatic associations (mostly granites!) 150 125 100 75 50 25 0 tps (Ma) Subduction stage • Trans-Himalayan batholith • Cretaceous-Oligocene • Similar to Andean or Cordileran (California, British Columbia, Japan…) plutons • I-types (Andean) Diorites Tonalites Granodiorites Granites Hornblende granodiorite Hbl-Biotite granodiorite Cpx Hbl Bt Major elements biotite muscovite cordierite andalusite garnet pyroxene hornblende biotite aegirine riebeckite arfvedsonite CaO CaO moles CaO K2O K2O Al2O3 K2O Na2O Peraluminous Al2O3 Al2O3 Na2O Metaluminous Na2O Peralkaline 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. Chapter 18: Granitoid Rocks Table 18-3. The S-I-A-M Classification of Granitoids SiO2 K2O/Na2O Type M 46-70% low Ca, Sr high I 53-76% low high in mafic rocks S 65-74% high low A/(C+N+K)* low Fe3+/Fe2+ Cr, Ni low 18O < 9‰ low < 9‰ low high > 9‰ var low var low low: metal- moderate uminous to peraluminous high metaluminous A high 77% Na2O high * molar Al2O3/(CaO+Na2O+K2O) low var peralkaline 87 Sr/86Sr Misc Petrogenesis < 0.705 Low Rb, Th, U Subduction zone Low LIL and HFS or ocean-intraplate Mantle-derived < 0.705 high LIL/HFS Subduction zone med. Rb, Th, U Infracrustal hornblende Mafic to intermed. magnetite igneous source > 0.707 variable LIL/HFS Subduction zone high Rb, Th, U biotite, cordierite Supracrustal Als, Grt, Ilmenite sedimentary source var low LIL/HFS Anorogenic high Fe/Mg Stable craton high Ga/Al Rift zone High REE, Zr High F, Cl Data from White and Chappell (1983), Clarke (1992), Whalen (1985) Trace elements Isotopes Mixed sources (mantle + some crust ?) Origin • Will be discussed during the « subduction » lectures Successive magmatic associations (mostly granites!) 150 125 100 75 50 25 0 tps (Ma) Collision stage • High Himalaya leucogranites • Miocene • S-type Granites ± Alk. Granites ± Granodiorites 2 micas granites Tourmaline granite Bt Kfs Ms Pl • • • • • Biotite Muscovite Tourmaline Garnet (Cordierite) Major elements biotite muscovite cordierite andalusite garnet pyroxene hornblende biotite aegirine riebeckite arfvedsonite CaO CaO moles CaO K2O K2O Al2O3 K2O Na2O Peraluminous Al2O3 Al2O3 Na2O Metaluminous Na2O Peralkaline 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. Chapter 18: Granitoid Rocks Table 18-3. The S-I-A-M Classification of Granitoids SiO2 K2O/Na2O Type M 46-70% low Ca, Sr high I 53-76% low high in mafic rocks S 65-74% high low A/(C+N+K)* low Fe3+/Fe2+ Cr, Ni low 18O < 9‰ low < 9‰ low high > 9‰ var low var low low: metal- moderate uminous to peraluminous high metaluminous A high 77% Na2O high * molar Al2O3/(CaO+Na2O+K2O) low var peralkaline 87 Sr/86Sr Misc Petrogenesis < 0.705 Low Rb, Th, U Subduction zone Low LIL and HFS or ocean-intraplate Mantle-derived < 0.705 high LIL/HFS Subduction zone med. Rb, Th, U Infracrustal hornblende Mafic to intermed. magnetite igneous source > 0.707 variable LIL/HFS Subduction zone high Rb, Th, U biotite, cordierite Supracrustal Als, Grt, Ilmenite sedimentary source var low LIL/HFS Anorogenic high Fe/Mg Stable craton high Ga/Al Rift zone High REE, Zr High F, Cl Data from White and Chappell (1983), Clarke (1992), Whalen (1985) Trace elements Isotopes Very « crustal » Origin 1. Lesser Himalaya 2. Formation I (Greywackes et métapélites) 3. Formation II (Gneiss calciques) 4. Formation III (Orthogneiss) 5. Sédiments tibétains 6. Leucogranite du Manaslu 7. Dykes Dalle du Tibet Les granites syncollisionels du Haut Himalaya Migmatites de la formation I Successive magmatic associations (mostly granites!) 150 125 100 75 50 25 0 tps (Ma) Late to post-collision stage • Syenites and alkali granites • Miocene to present • A-type • N.B. Some « sub-alkali », « Mg-K » I-types (cf. Vredenburg pluton as seen in Paternoster) are also emplaced at this stage Le magmatisme « post-collisionel » himalayen Cas du magmatisme Néogène du Sud Karakorum Syenites Qtz. Syenites Granites Alk. granites Cpx, Fe-rich Sometimes Na-Cpx or Amph Little/no plag (Riebeckite, Aegyrine Ardfersonite) Major elements biotite muscovite cordierite andalusite garnet pyroxene hornblende biotite aegirine riebeckite arfvedsonite CaO CaO moles CaO K2O K2O Al2O3 K2O Na2O Peraluminous Al2O3 Al2O3 Na2O Metaluminous Na2O Peralkaline 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. Chapter 18: Granitoid Rocks Table 18-3. The S-I-A-M Classification of Granitoids SiO2 K2O/Na2O Type M 46-70% low Ca, Sr high I 53-76% low high in mafic rocks S 65-74% high low A/(C+N+K)* low Fe3+/Fe2+ Cr, Ni low 18O < 9‰ low < 9‰ low high > 9‰ var low var low low: metal- moderate uminous to peraluminous high metaluminous A high 77% Na2O high * molar Al2O3/(CaO+Na2O+K2O) low var peralkaline 87 Sr/86Sr Misc Petrogenesis < 0.705 Low Rb, Th, U Subduction zone Low LIL and HFS or ocean-intraplate Mantle-derived < 0.705 high LIL/HFS Subduction zone med. Rb, Th, U Infracrustal hornblende Mafic to intermed. magnetite igneous source > 0.707 variable LIL/HFS Subduction zone high Rb, Th, U biotite, cordierite Supracrustal Als, Grt, Ilmenite sedimentary source var low LIL/HFS Anorogenic high Fe/Mg Stable craton high Ga/Al Rift zone High REE, Zr High F, Cl Data from White and Chappell (1983), Clarke (1992), Whalen (1985) Trace elements Isotopes 10 Asthénosphère 5 eNd 0 -5 Composite (mantle + crust), with some mantle-derived units and some crustal units -10 -15 leucogranites du Haut Himlaya, 20 Myr -20 0.70 0.71 0.72 0.73 0.74 0.75 0.76 0.77 86Sr/87Sr Sud Karakorum Hemasil, 8 Myr Hunza, 4 -25 Myr Baltoro, 17-25 Myr Sud Tibet, 10-16 Myr Sud Tibet, 17 Myr Sud Tibet, 18-23 Myr Sud Tibet, 23 - 25 Myr Origin • Shear heating • Slab breakoff « Shear heating » ? Chaleur de frottement Karakorum Kunlun BALTORO MKT N K2 HEMASIL MMT Lamprophyres South Tibet neogenous magmatism North Tibet neogenous magmatism Himalaya Tibetan plateau MCT 200km MBT ITSZ « Slab breakoff » Conclusion (1): a succession of granite types • Subduction (pre-collision): I « andean » • Syn-collision: S-type leucogranites • Post-collision : A (and I « Mg-K ») This is, of course, a very simplified view ! Conclusion (2): Types of granitoids Table 18-3. The S-I-A-M Classification of Granitoids SiO2 K2O/Na2O Type M 46-70% low Ca, Sr high I 53-76% low high in mafic rocks S 65-74% high low A/(C+N+K)* low Fe3+/Fe2+ Cr, Ni low 18O < 9‰ low < 9‰ low high > 9‰ var low var low low: metal- moderate uminous to peraluminous high metaluminous A high 77% Na2O high * molar Al2O3/(CaO+Na2O+K2O) low var peralkaline 87 Sr/86Sr Misc Petrogenesis < 0.705 Low Rb, Th, U Subduction zone Low LIL and HFS or ocean-intraplate Mantle-derived < 0.705 high LIL/HFS Subduction zone med. Rb, Th, U Infracrustal hornblende Mafic to intermed. magnetite igneous source > 0.707 variable LIL/HFS Subduction zone high Rb, Th, U biotite, cordierite Supracrustal Als, Grt, Ilmenite sedimentary source var low LIL/HFS Anorogenic high Fe/Mg Stable craton high Ga/Al Rift zone High REE, Zr High F, Cl Data from White and Chappell (1983), Clarke (1992), Whalen (1985) More granie classification Table 18-4. A Classification of Granitoid Rocks Based on Tectonic Setting. After Pitcher (1983) in K. J. Hsü (ed.), Mountain Building Processes, Academic Press, London; Pitcher (1993), The Nature and Origin of Granite, Blackie, London; and Barbarin (1990) Geol. Journal, 25, 227-238. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Table 18-4. A Classification of Granitoid Rocks Based on Tectonic Setting. After Pitcher (1983) in K. J. Hsü (ed.), Mountain Building Processes, Academic Press, London; Pitcher (1993), The Nature and Origin of Granite, Blackie, London; and Barbarin (1990) Geol. Journal, 25, 227-238. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.