Presentation is loading. Please wait.

Presentation is loading. Please wait.

Contact and shape of plutons And some enigmatic features…

Similar presentations


Presentation on theme: "Contact and shape of plutons And some enigmatic features…"— Presentation transcript:

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 Hoedjiespunt granite (552Ma) Saldanha quartz porphyry (515Ma)

5 2.7 Ga Kangaatsiaq granite, W. Greenland

6

7

8

9 Contact aureole Flamanville, France

10 Chilled margin

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

12

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 Jamestown Schist belt Nelshoogte pluton

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)

18

19 Dyke swarms

20 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. Deformed contacts

21 Sea Point Contact between granite and Malmesbury metasediments

22

23

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

25

26

27

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. After Anhaeusser et al. (1981) Anhaeusser (2001). 5 km N

30 Enclaves Source-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 Vredenburg granite (540 Ma), Britannia Bay, RSA MME

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

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

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 Kangaatsiaq pluton, W. Greenland

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

43 NWSE Synthetic cross-section Flat pluton (subsequently folded)

44 Gravitationnal studies Bouguer anomaly Depth of pluton floor

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 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. Structures and Field Relationships

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

54

55 Laccoliths

56

57

58 Sills Karoo dolerites

59

60 Most intrusions are rather flat

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

62 « Flat » and « long » plutons

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

64

65 Pluton shapes reflect strain pattern… 11 33

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

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 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. Modern conceptions: flat batholiths


Download ppt "Contact and shape of plutons And some enigmatic features…"

Similar presentations


Ads by Google