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
9
(No Transcript)
10
Remontéedel Indeet collision à55 Ma
11
(No Transcript)
12
The subduction stage
Les témoins de la subduction de l Inde sous
l Asie
13
(No Transcript)
14
The collision stage
Les témoins de la collision continentale
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
The  late to post  collision stage
19
(No Transcript)
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
(No Transcript)
25
(No Transcript)
26
Cpx Hbl Bt
27
(No Transcript)
28
Major elements

• .. See assignment

29
Trace elements
30
(No Transcript)
31
Isotopes

• Mixed sources (mantle some crust ?)

32
Origin

• Will be discussed during the  subduction 
  lectures

33
(No Transcript)
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
37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
2 micas granites
Tourmaline granite
44

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

45
Major elements

• .. See assignment

46
Trace elements
47
(No Transcript)
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
(No Transcript)
57
(No Transcript)
58
Major elements

• .. See assignment

59
Trace elements
60
(No Transcript)
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