Part II – Important igneous associations 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

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

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

Remontée de l ’Inde et collision à 55 Ma

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

collision continentale The collision stage Les témoins de la collision continentale

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

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

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 Ms Kfs Pl

Biotite Muscovite Tourmaline Garnet (Cordierite)

Major elements

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

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

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

Major elements

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

Trace elements

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

Origin Shear heating Slab breakoff

« Shear heating » ? Chaleur de frottement

« 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

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.