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Igneous petrology

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)

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Igneous petrology

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  1. Igneous petrology Part II – Important igneous associations

  2. 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)

  3. Granites and collisions Exemple of the Himalaya

  4. 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

  5. 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

  6. Rifting of continental crust to form a new ocean basin

  7. 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)

  8. Himalayan collision

  9. Remontéedel ’Indeet collision à55 Ma

  10. The subduction stage Les témoins de la subductionde l ’Inde sous l ’Asie

  11. Les témoins de la collision continentale The collision stage

  12. The « late to post » collision stage

  13. Successive magmatic associations (mostly granites!) 150 125 100 75 50 25 0 tps (Ma)

  14. Subduction stage • Trans-Himalayan batholith • Cretaceous-Oligocene • Similar to Andean or Cordileran (California, British Columbia, Japan…) plutons • I-types (Andean)

  15. Diorites Tonalites Granodiorites Granites

  16. Hornblende granodiorite Hbl-Biotite granodiorite

  17. Cpx Hbl Bt

  18. Major elements

  19. 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.

  20. Chapter 18: Granitoid Rocks

  21. Trace elements

  22. Isotopes Mixed sources (mantle + some crust ?)

  23. Origin • Will be discussed during the « subduction » lectures

  24. Successive magmatic associations (mostly granites!) 150 125 100 75 50 25 0 tps (Ma)

  25. Collision stage • High Himalaya leucogranites • Miocene • S-type

  26. Granites ± Alk. Granites ± Granodiorites

  27. Bt Kfs Ms Pl 2 micas granites Tourmaline granite

  28. Biotite • Muscovite • Tourmaline • Garnet • (Cordierite)

  29. Major elements

  30. 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.

  31. Chapter 18: Granitoid Rocks

  32. Trace elements

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