1. Part II – Important igneous associations
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. Collision – welding together of continental crust
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

10. Remontée de l ’Inde et collision à 55 Ma

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

14. collision continentale
The collision stage
Les témoins de la
collision continentale

18. The « late to post » collision stage

20. Successive magmatic associations
(mostly granites!)
tps (Ma)

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

22. Diorites
Tonalites
Granodiorites
Granites

23. Hornblende granodiorite
Hbl-Biotite granodiorite

26. Cpx
Hbl Bt

28. Major elements

29. Figure 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.

30. Chapter 18: Granitoid Rocks

31. Trace elements

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

34. Origin
Will be discussed during the « subduction » lectures

36. Successive magmatic associations
(mostly granites!)
tps (Ma)

37. Collision stage
High Himalaya leucogranites
Miocene
S-type

38. Granites
± Alk. Granites
± Granodiorites

45. 2 micas granites
Tourmaline granite Bt Ms
Kfs Pl

46. Biotite
Muscovite
Tourmaline
Garnet
(Cordierite)

47. Major elements

48. Figure 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.

49. Chapter 18: Granitoid Rocks

50. Trace elements

52. Isotopes
Very « crustal »

53. 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

54. Les granites syncollisionels du Haut Himalaya
Migmatites de la formation I

55. Successive magmatic associations
(mostly granites!)
tps (Ma)

56. 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

57. Le magmatisme « post-collisionel » himalayen
Cas du magmatisme Néogène du Sud Karakorum

58. Syenites
Qtz. Syenites
Granites
Alk. granites

59. Sometimes Na-Cpx or Amph
Cpx, Fe-rich
Sometimes Na-Cpx or Amph
Little/no plag
(Riebeckite, Aegyrine
Ardfersonite)

62. Major elements

63. Figure 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.

64. Chapter 18: Granitoid Rocks

65. Trace elements

67. Isotopes
Composite (mantle + crust), with some mantle-derived units and some crustal units

68. Origin
Shear heating
Slab breakoff

69. « Shear heating » ?
Chaleur de frottement

70. « Slab breakoff »

71. 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 !

72. Conclusion (2): Types of granitoids

73. More granie classification
Table 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, Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

74. Table 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, Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.