Title: Igneous petrology
1Igneous petrology
- Part III 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)
3Granites and collisions
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
5Subducting 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
6Rifting of continental crust to form a new ocean
basin
7The Himalayas geodynamic context
- India-Eurasia convergence
- Destruction of the Tethys ocean
- Subduction stage (gt 100 Ma 25 Ma
Cretaceous-Oligocene) - Collision stage (25 Ma present Miocene and
Pliocene) - Post-collision stage (present)
8Himalayan collision
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10Remontéedel Indeet collision à55 Ma
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12The subduction stage
Les témoins de la subduction de l Inde sous
l Asie
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14The collision stage
Les témoins de la collision continentale
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18The late to post collision stage
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20Successive magmatic associations (mostly
granites!)
150 125 100 75
50 25 0 tps (Ma)
21Subduction stage
- Trans-Himalayan batholith
- Cretaceous-Oligocene
- Similar to Andean or Cordileran (California,
British Columbia, Japan) plutons - I-types (Andean)
22Diorites Tonalites Granodiorites Granites
23Hornblende granodiorite
Hbl-Biotite granodiorite
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26Cpx Hbl Bt
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28Major elements
29Trace elements
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31Isotopes
- Mixed sources (mantle some crust ?)
32Origin
- Will be discussed during the subduction
lectures
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34Successive magmatic associations (mostly
granites!)
150 125 100 75
50 25 0 tps (Ma)
35Collision stage
- High Himalaya leucogranites
- Miocene
- S-type
36Granites Alk. Granites Granodiorites
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432 micas granites
Tourmaline granite
44- Biotite
- Muscovite
- Tourmaline
- Garnet
- (Cordierite)
45Major elements
46Trace elements
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48Isotopes
49Origin
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
50Les granites syncollisionels du Haut Himalaya
Migmatites de la formation I
51Successive magmatic associations (mostly
granites!)
150 125 100 75
50 25 0 tps (Ma)
52Late 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
53Le magmatisme post-collisionel himalayen Cas
du magmatisme Néogène du Sud Karakorum
54Syenites Qtz. Syenites Granites Alk. granites
55Cpx, Fe-rich Sometimes Na-Cpx or Amph Little/no
plag
(Riebeckite, Aegyrine Ardfersonite)
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58Major elements
59Trace elements
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61Isotopes
Composite (mantle crust), with some
mantle-derived units and some crustal units
62Origin
- Shear heating
- Slab breakoff
63 Shear heating ?
Chaleur de frottement
64 Slab breakoff
65Conclusion 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 !
66Trace elements are markers
- Of the different types of magmas
- Of their origin
67- Ba fluid mobile element
- Rb strongly incomp.element
68- Zr fluid immobile,relatively depelted in the
crust but not in the mantle
69Assignment for this week
- Read from J.D. Winter, Chapter 18, pages 343361
- Material available for discussion
- Thin sections and samples of Cape Granite Suite
I, A and S granites, to be used as examples - Your field observations, photos and notes from 1
and 2 April - An excel table with composition of examples of I,
S and A granites - This lecture, for additional examples.
- Assignment
- Propose a comparison table for I, S and A
granites, including - Field characteristics
- Mineralogy texture
- Chemical and/or normative composition
- Possible sources and evolution of the magmas
- Typical geodynamical context or contexts
- And any other interesting features you can think
of ! - Obviously, you will need either a very big table,
or a lot of attached explanatory notes, graphs,
sketches, etc