1. Contact and shape of plutons
And some enigmatic features…

2. Contacts Sharp contacts Deformed/synfolial contacts
Progressive contacts

3. Sharp contacts
Torres del Paine, S. Chile

4. Contact - Hoedjiespunt granite and Saldanha quartz porphyry
Saldanha quartz porphyry (515Ma)
Hoedjiespunt granite (552Ma)

5. 2.7 Ga Kangaatsiaq granite, W. Greenland

9. Contact aureole
Flamanville, France

10. Chilled margin

11. Breccias, dykes, transition zones
Figure Continuity of foliation across an igneous contact for a pre- or syn-tectonic pluton. From Compton (1962), Manual of Field Geology. © R. Compton.

13. 2.9 – 2.7 Ga granites
3.1 Ga granites
& syenites
Moodies
Fig Tree
Onverwacht
Ca. 3.2 Ga TTG
Ca. 3.4 Ga TTG
« Ancient gneisses »
(3.6 – 3.4 Ga)

14. Geology of the Nelshoogte pluton
5 km

15. Nelshoogte pluton
Jamestown Schist belt

16. Intrusive breccias

17. 2.9 – 2.7 Ga granites
3.1 Ga granites
& syenites
Moodies
Fig Tree
Onverwacht
Ca. 3.2 Ga TTG
Ca. 3.4 Ga TTG
« Ancient gneisses »
(3.6 – 3.4 Ga)

19. Dyke swarms

20. Deformed contacts
Figure Marginal foliations developed within a pluton as a result of differential motion across the contact. From Lahee (1961), Field Geology. © McGraw Hill. New York.

21. Sea Point Contact between granite and Malmesbury metasediments

24. Progressive contacts
Figure Gradational border zones between homogeneous igneous rock (light) and country rock (dark). After Compton (1962), Manual of Field Geology. © R. Compton.

28. Contacts can be combinations of…
Injection
Deformation
Melting/in situ reactions
Things to consider on Wednesday!

29. Dome & keel structures in the Barberton granitoid-greenstone terrain
Domes:
3.4 & 3.2 Ga gneissic TTG`s
Concentric foliation patterns concordant with foliation in the surrounding supracrustals
Keels:
tightly folded synformal supracrustals with TPC`s.
5 km
After Anhaeusser et al. (1981)
Anhaeusser (2001).

30. Enclaves Source-related Emplacement related
MME (microgranular mafic enclaves)
Restites (« surmicaceous » enclaves)
Emplacement related
Xenoliths
Microgranular felsic enclaves (« chilled margin »)

31. MME
Hoedjiespunt granite (540 Ma), Saldanha, RSA

32. MME
Vredenburg granite (540 Ma), Britannia Bay, RSA

33. Surmicaceous?
Hoedjiespunt granite (540 Ma), Saldanha, RSA

34. Surmicaceous?
Hoedjiespunt granite (540 Ma), Saldanha, RSA

35. Xenolith
Hoedjiespunt granite (540 Ma), Saldanha, RSA

36. Xenolith

37. Microgranular felsic
Hoedjiespunt granite (540 Ma), Saldanha, RSA

38. Table Didier, J. and Barbarin (1991) The different type of enclaves in granites: Nomenclature. In J. Didier and B. Barbarin (1991) (eds.), Enclaves in Granite Petrology. Elsevier. Amsterdam, pp

39. Try to sketh two different contacts:
A shallow intrusive, emplaced in a low strain situation
A deep intrusive, syntectonic

40. Studying pluton shapes
Map pattern
Internal structures
Geophysics

41. Kangaatsiaq pluton, W. Greenland

42. amphibolites and Bt-gneisses
A key outcrop
Kangaatsiaq
Granite
Interstratified
amphibolites and Bt-gneisses
Orthogneiss
Site jfm-089

43. Synthetic cross-sectionNW SE
Flat pluton
(subsequently folded)

44. Gravitationnal studies
Depth of pluton floor
Bouguer anomaly

45. Internal structures

46. Coupling different approaches: Cabeza de Araya, Spain

47. Cabeza de Araya
Depth of pluton floor vs. Lineation plunge

48. Cabeza de Araya
Link with chemical composition

49. Shape of plutons Mostly flat (contrarily to what you might think…)
Sometimes wedge shaped
Rare « vertical » intrusions
First order approximation: they reflect emplacement stress field

50. Structures and Field Relationships
Figure Block diagram several kilometers across, illustrating some relationships with the country rock near the top of a barely exposed pluton in the epizone. The original upper contact above the surface is approximated by the dashed line on the front plane. From Lahee (1961), Field Geology. © McGraw Hill. New York.

51. 2.9 – 2.7 Ga granites
3.1 Ga granites
& syenites
Moodies
Fig Tree
Onverwacht
Ca. 3.2 Ga TTG
Ca. 3.4 Ga TTG
« Ancient gneisses »
(3.6 – 3.4 Ga)

52. Flat plutons
3.1 Ga Mpuluzi batholith, Barberton

53. ..\..\perso\sites web\free-moyen\za\img\swazzi-mountains.jpg

55. Laccoliths

58. Sills
Karoo dolerites

60. Most intrusions are rather flat

61. Wedge-shaped intrusions
Closepet, 2.5 Ga, South India

62. « Flat » and « long » plutons

63. “Vertical” intrusions
Figure Schematic block diagram of some intrusive bodies.

65. Pluton shapes reflect strain pattern…

66. Batholiths Plutons associations Definition not too clear
Old litterature: « primordial » granitic level, somewhere down.
Modern conceptions: associations of individual plutons, each with its shape and structures
Probably rather flat as well!

67. “Vertical” intrusions
Figure Schematic block diagram of some intrusive bodies.

68. An “old” view of a batholith
Figure Schematic cross section of the Coastal batholith of Peru. The shallow flat-topped and steep-sided “bell-jar”-shaped plutons are stoped into place. Successive pulses may be nested at a single locality. The heavy line is the present erosion surface. From Myers (1975) Geol. Soc. Amer. Bull., 86,

69. Modern conceptions: flat batholiths
Figure Diagrammatic cross section of the Boulder Batholith, Montana, prior to exposure. After Hamilton and Myers (1967), The nature of batholiths. USGS Prof. Paper, 554-C, c1-c30.