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Igneous petrology

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Title: Granites and collisions Author: Information Technology Last modified by: Information Technology Created Date: 4/6/2006 1:53:40 PM Document presentation format – PowerPoint PPT presentation

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Title: Igneous petrology


1
Igneous 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)

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 (gt 100 Ma 25 Ma
    Cretaceous-Oligocene)
  • Collision stage (25 Ma present Miocene and
    Pliocene)
  • Post-collision stage (present)

8
Himalayan collision
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10
Remontéedel Indeet collision à55 Ma
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12
The subduction stage
Les témoins de la subduction de l Inde sous
l Asie
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14
The collision stage
Les témoins de la collision continentale
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18
The  late to post  collision stage
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20
Successive magmatic associations (mostly
granites!)
150 125 100 75
50 25 0 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
24
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26
Cpx Hbl Bt
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28
Major elements
  • .. See assignment

29
Trace elements
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31
Isotopes
  • Mixed sources (mantle some crust ?)

32
Origin
  • Will be discussed during the  subduction 
    lectures

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34
Successive magmatic associations (mostly
granites!)
150 125 100 75
50 25 0 tps (Ma)
35
Collision stage
  • High Himalaya leucogranites
  • Miocene
  • S-type

36
Granites Alk. Granites Granodiorites
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43
2 micas granites
Tourmaline granite
44
  • Biotite
  • Muscovite
  • Tourmaline
  • Garnet
  • (Cordierite)

45
Major elements
  • .. See assignment

46
Trace elements
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48
Isotopes
  • Very  crustal 

49
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
50
Les granites syncollisionels du Haut Himalaya
Migmatites de la formation I
51
Successive magmatic associations (mostly
granites!)
150 125 100 75
50 25 0 tps (Ma)
52
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

53
Le magmatisme  post-collisionel  himalayen Cas
du magmatisme Néogène du Sud Karakorum
54
Syenites Qtz. Syenites Granites Alk. granites
55
Cpx, Fe-rich Sometimes Na-Cpx or Amph Little/no
plag
(Riebeckite, Aegyrine Ardfersonite)
56
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58
Major elements
  • .. See assignment

59
Trace elements
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61
Isotopes
Composite (mantle crust), with some
mantle-derived units and some crustal units
62
Origin
  • Shear heating
  • Slab breakoff

63
 Shear heating  ?
Chaleur de frottement
64
 Slab breakoff 
65
Conclusion 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 !
66
Trace 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

69
Assignment 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
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