Foliation

FOLIATION AND TYPES

1. FOLIATION AND THEIR TYPES Guided By- Presented By- Dr. Poonam Bhatnagar Parag Sonwane Class – M.Sc.(1 st Sem.) Govt. Holkar Science College Indore (M.P.) 1

2. CONTENT What is foliation. Fabric and cleavage. Development and effects of foliation. Classification of foliation. Genetic classification. 1.a) primary foliation. 1.b) secondary foliation. 1.c) inherited foliation. Morphological classification. 2.a) spaced foliation. 2.b) continuous foliation Significance of foliation. Conclusion. References. 2

3. FOLIATION Derived from word folium which means leaf-like. Fabric forming planar or curvi-planar structure in a metamorphic rock,but may also include primary sedimentary bedding or magmatic layering. 3

4. (Fig. FABRIC OF ROCK) FABRIC Describes the spatial and geometric configuration of all the elements that makes a rock. 4

5. CLEAVAGE The property of a rock to split along a regular set of sub parallel,closely spaced planes. 5

6. 6

7. 7

8. EFFECTS ON ROCKS Rhythmic bedding in sedimentary rocks. Compositional layering in igneous rock. Planar alignment of sedimentary clasts. Parallel alignment of conglomerate pebbles. S-C foliation in metamorphic rocks. 8

9. GENETIC CLASSIFICATION PRIMARY FOLIATION Form during the deposition of sediments and formation of magmatic rocks. Eg:bedding in sedimentary rocks,flow banding in lavas and magmatic layering in intrusive rocks. 9

10. Fig.- Flow banding In Rhyolite 10

11. SECONDARY FOLIATION Products of stress and strain and most are tectonic foliations.They form in response to tectonic stress. Eg:axial plane cleavages in metamorphic rocks. 11

12. The two basic forms of secondary foliation are - Rock cleavage. Schistosity. 12

13. Type of secondary foliation Bedding cleavage. Fracture cleavage. Slaty cleavage or schistosity. Slip cleavage. Shear cleavage. Axial plane cleavage. 13

14. Bedding Cleavage In some metamorphic rock the cleavage is parallel to the bedding and hence it may be called bedding cleavage or bedding schistosity. 14

15. Slaty Cleavage or Schistosity Slaty cleavage is diagonal to the bedding, it is more or less by parallel to the axial plane of the fold. Ex. Slate 15

16. Slip Cleavage This feature is also called strain-slip cleavage and crenulations cleavage. In many metamorphic terrenes the schistosity may be crinkled into small folds with a wavelength of a fraction of an inch. one limb of these small folds becomes a zone of weakness. 16

17. Shear Cleavage Shear cleavage is a fracture cleavage along which displacement has taken place. 17

18. Fracture Cleavage Fracture cleavage is essentially a closed spaced jointing; the minerals in the rocks are not parallel to the cleavage. 18

19. Axial Plane Cleavage Cleavage or schistosity that is essentially parallel to the axial planes of the folds is called axial plane cleavage. The term is generally used in combination with one of term given above. 19

20. Inherited Foliation The primary foliation is giving in the igneous rocks. Then the igneous rocks may be changes in the metamorphic rocks. After present foliation it is inherited foliation. 20

21. MORPHOLOGICAL CLASSIFICATION 21

22. SPACED FOLIATION Fabric elements are not homogeneously distributed. The rock is divided into lenses or layers of different composition. Space between individual folium and domain is 10µm to 10 cm.If it increases to more than 10 cm. It is grouped into joints. Micrelithon is rock mass between two domains. 22

23. Fig.- Spaced Foliation 23

24. COMPOSITIONAL FOLIATION Compositional foliations are marked by the layers or lamina of different mineralogical composition. A planar alignment of platy or niddle like crystals may be present. 24

25. 25

26. COMPOSITIONAL FOLIATIONS Diffused Characterised by, Widely spaced Weak concentrations of minerals predominately of single lithology Common in ultra-mafic rocks b. BANDED Characterised by, Relatively closed spaced compositional layers Minerologocally distinct and compare-able abundance Common in high grade metamorphic gneisses 26

27. DISJUNCTIVE FOLIATION Disjunctive word derived from disjunctus a latin word which means disjoined. A foliation that is formed in sedimentary rocks that have been subjected to tectonic differential stress under metamorphic conditions. It is defined by array of subparallel fabric elements called cleavage domain, in which the original rock fabric and composition have been markedly changed by the process of pressure solution. 27

28. 0n the basis of smoothness or regularity of cleavage domains, disjunctive foliation is divided into four groups. STYLOLITIC ANASTOMOSING ROUGH SMOOTH 28

29. STYLOLITIC DISJUNCTIVE FOLIATIONS Cleavage domain are long, continuous but very irregular. This type of foliations is typically in limestone in which cleavage domains are characteristically are thin,dark,clay seams. 29

30. ANASTOMOSING DISJUNCTIVE FOLIATIONS Cleavage domains are long,continuous,wavey forming and irregular network outlining lenticular microlithons. Such foliations are common in limestone and in phyllites and schists. 30

31. ROUGH DISJUNCTIVE FOLIATIONS Cleavage domains are short. Discontinuous concentration of highly oriented platy minerals. Typically abundant in rocks containing sand sized minerals. 31

32. SMOOTH DISJUNCTIVE FOLIATIONS Cleavage domains are long, continuous and smooth. Have the concentrations of highly oriented platy minerals. 32

33. 33

34. CRENULATION FOLIATIONS Microlithons contains the micro folds of an earlier foliation. Crenulations foliation are formed by the harmonic wrinkles or chevron folds in pre-existing foliation, the new foliation cut across the old foliation. 34

35. 35

36. CONTINEOUS FOLIATIONS Continuous foliation are defined either by with a spacing less than 10 micro-meter or by non-domain structure. Fabric element are homogeneously distributed. Consists of a non-layered homogeneous distribution of platy mineral grains with a preferred orientation. 36

37. 37

38. CONTINEOUS FOLIATION Fine continuous foliation e.g. slate Coarse continuous foliation e.g. schist 38

39. SIGNIFICANCE OF FOLIATION Can help to unravel the tectonic and metamorphic evolution of an area. Relative growth periods of metamorphic minerals. Deformation phases in an area. Help to determine the geometry of folding. 39

40. Relation to major structure Foliations have the major relation with the fold and folded structure. Foliation are generally related to linear structure. 40

41. CONCLUSION Foliations are common in metamorphic rocks. Without foliations it would be difficult to do proper structural analysis. Give us important strain information where regular strain markers are absent. Different types of foliations reflect variations in lithology and temperature or depth of burial during deformation. 41

42. REFERENCES Jain A.K(2014), An introduction to Structural Geology,( Geological society of india),pp. 361-388 Twiss R.J. and Moores E.M.,Structural Geology,(W.H. Freeman & Company), New York, pp. 298-306 Website(02/10/2019)- https://www.slideshare.net. 42

43. Thank you. 43