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Analysis and interpretation of foliation and lineation

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Foliation and lineation are important fabric elements in structural geology. Foliation refers to any closely spaced planar structures in rocks, such as layering, and develops through processes like deformation and metamorphism. There are different types of foliation including primary, diagenetic, and secondary foliation. Lineation describes any linear structures in rocks, such as the alignment of minerals, and develops through processes associated with folds, boudins, and the intersection of planar fabrics. Foliation and lineation provide insight into the tectonic and metamorphic evolution of geological areas.

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 INTRODUCTION  FOLIATION  Foliation Includes  Significanceof Foliation  Primary Foliation  Diagenetic Foliation  Secondary Foliation  Two general typesof foliation:  Relationship of Foliation to Folds  LINEATION  Classification form lineations, Surfacelineations, and mineral lineations  CONCLUSION  REFERENCES 31-08-2012 2

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 In structural geology the term fabrics mean the arrangement of component featuresof therock.  Fabricsinclude-foliation and leneation  Foliation is any closely-spaced, systematically oriented planar feature that occurs penetratively in a body of rock, and commonly associated with folds.it is a characteristic of tectonites, i.e., rocks formed by deformation which are commonly, but not necessarily, metamorphosed.  Leneation-Leneation isafabric element which can berepresent a line.It can beassociated with other structuressuch asfold, bouldins.It may represent on thesurfaceof therock body and sometimeit reflect thearrangement of themineral grain. 31-08-2012 3

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 A homogeneously distributed planar structurein arock.  Foliation isacharacteristic of tectonites, i.e., rocksformed by deformation which arecommonly, but not necessarily, metamorphosed.  spatial variation in mineral composition or grain size.  preferred orientation of platy grainsin a matrix without fabric. e.g., micain micaceousquartziteor gneiss.  preferred orientation of grain boundaries of deformed elongategrains./lenticular mineral/grain aggregates.  e.g., elongatequartz or calcite.. 31-08-2012 4

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31-08-2012 5 a. Compositional layering b. B.grain size variation c. Closely spaced d. Preferred orientation of grain boundaries e. Preferred orientation of platy minerals f. Combination of a+e this is very common in both sedimentary and metamorphic rocks

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 Rhythmic bedding in sedimentary rocks  Compositional layering in igneousrocks  planar alignment of sedimentary clasts.  parallel alignment of conglomeratepebbles.  planar alignment of fused clastsin ignimbrite  S-C foliation in metamorphic rocks  Excludesjointsbecausethey arenot sufficiently penetrative. 31-08-2012 6

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Deformed terrainscommonly haveseveral successivegenerationsof foliation. 1. If thesecan bedistinguished from oneanother by typeand age (cross-cutting relationships, absoluteagedates, and overprinting under microscope), ▪ can help to unravel thetectonic and metamorphic evolution of an area. 1. Foliationscan beused to asreferencestructuresto establish the: ▪ relativegrowth periodsof metamorphic minerals, especially porphyroblasts ▪ deformation phasesin an area. Foliation may be related to folds, however, foliation ismorepenetrativethan related foldsand thereforecan beseen better. 31-08-2012 7

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 Structures related to the original rock-forming process.  Originated by sedimentary processes such astransport and deposition: ▪ Bedding ▪ preferred orientation of sedimentary clasts  Originated by primary igneous processes such asflow and crystallization: ▪ magmatic layering in igneousrocks ▪ preferred orientation of bubblesand pumicefragments 31-08-2012 8

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 Formsby diagenetic processessuch ascompaction in sedimentswith detrital mica.  Arealso known asbedding-parallel foliation.  Observed in very low and low-gradepelitic sedimentswhich have undergonelittleor no deformation.  Isdefined by parallel orientation of thin elongatedetrital micagrainswith frayed edges.  Themicasarecommonly subparallel to bedding.  Thepreferred orientation of themicasisdueto their passiverotation.  Diagenetic foliation isnot associated with folds.  It precedestheformation of secondary foliation.  It playsan important rolein development of secondary foliation in pelites. 31-08-2012 9

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 Formsafter lithification and crystallization of rocks.  Formsby somekind of differentiation processin astressfield.  Iscommonly (sub)parallel to thefold axial plane.  Isrelated to strain (parallel to theXY plane) and deformed features.  Formsasaresult of:  ductiledeformation (by crystal plasticity or cataclastic flow)  metamorphism.  Includes:  cleavage  schistosity  differentiated compositional layering  mylonitic foliation (Sand C) 31-08-2012 10

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 Cleavage – Traditionally: the property of a rock to split along a regular set of sub- parallel, closely-spaced planes – A more general concept adopted by some geologists is to consider cleavage to be any type of foliation in which the aligned platy phyllosilicates are too fine grained to see individually with the unaided eye Schistosity – A preferred orientation of inequaint mineral grains or grain aggregates produced by metamorphic processes – Aligned minerals are coarse grained enough to see with the unaided eye – The orientation is generally planar, but linear orientations are not excluded 31-08-2012 11

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Spaced foliation Continuous foliation 31-08-2012 12

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 Rock consists of two types of domains:  1. Cleavage domain: ▪ Planar, and havefabric elements subparallel to thetrend of thedomain. ▪ In metapelites, it isrich in micaand other mineralssuch asilmenite, graphite, rutile, apatite, and zircon. 31-08-2012 13 2. Microlithons liebetween cleavagedomains contain fabric elementswith weak or no preferred orientation may contain fabric elementsobliqueto thecleavagedomains. Fabric elements are not homogeneously distributed. The rock is divided into lenses or layers of different composition.

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Fabric elementsarehomogeneously distributed, to thescaleof grain individual minerals. Consistsof anon-layered homogeneous distribution of platy mineral grainswith apreferred orientation. - mineralsarecommonly micaand amphibole; sometimesquartz, etc. Theterminology isbased on observation under themicroscope. 31-08-2012 14 Fabric elements such as grain shape and size are used to classify continuous foliations. - Continuous Schistosity: grainsdefining thefoliation arevisibleby theunaided eye. - Continuous Cleavage or slaty cleavage: grainsarefiner and need microscope.

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 Foliation is commonly associated with folds.  Foliation in the hinge zone of a fold is parallel to the axial plane of the fold.  Foliation on the fold limbs may fan around the axial plane  Foliation may be refracted at boundaries between layers of different lithology.  Convergent fan - foliation converges from the convex toward the concave side of the folded layer, e.g., in competent rocks such as sandstone.  Divergent fan - foliation diverges from the convex toward the concave side of the folded layer, e.g., in the less competent rocks such as shale or schist.  Foliation formed by folding should be more steeply inclined than bedding on the fold limbs unless the fold has been overturned. 31-08-2012 15

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 Leneation isafabric element which can berepresent aline.  Theword lineation isused to describeany lenear structurethat occursrepetitively in asampleof rock  Leneation can beassociated with other structuressuch asfold, bouldins  It may represent on thesurfaceof therock body and sometimeit reflect thearrangement of the mineral grain. 31-08-2012 16

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31-08-2012 17 a.Simple linear fabric defined by preferreed orientation of linear bodies b.Combined lineation and foliation defined by prefeered orintation of elongate tabular bodies c.Linear fabrics defined by common axis of intersection of variably oriented, tabular bodies d. Linear fabrics defined by penitrative folding e.Lineation defined by intersection of 2 foliations a.Simple linear fabric defined by preferreed orientation of linear bodies b.Combined lineation and foliation defined by prefeered orintation of elongate tabular bodies c.Linear fabrics defined by common axis of intersection of variably oriented, tabular bodies d. Linear fabrics defined by penitrative folding e.Lineation defined by intersection of 2 foliations

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Leneation broadly divided into into three categories: form lineations, Surface lineations, and mineral lineations 31-08-2012 18

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 The hinge of any fold is a linear feature,the folds are might be closely or widely spaced.It is the fold hinges effectively define a rock fabric that can be measured as a fold hinge lineation.  Boudins are tablet-shaped lenses of a relatively rigid lithology, embedded in a weaker matrix, that have collectively undergone layer- parallel stretching 31-08-2012 19

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▪ An intersection lineation isalinear fabric element formed by, asthenamesuggests, theintersection of two planar fabric elements. 31-08-2012 20

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 Fabric element definesthis leneation isthesizeof mineral grain or theclustur of the mineral grain.  Mineral leneation commonly occur in foliation planeof metamorphic rock and in plane of mylonitic foliation.  Thisismainly caused by structing (stress,strain) and generally called structural leneation. 31-08-2012 21 e lineation on a bedding plane. Proterozoic Marinoan Group. Hallett Cove, South Australia. [-35.07

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 Metamorphic rockstherearecommonly pervasivesurfacesdefined by dis continuities, preferred orientation of inequant minerals, laminar mineral aggregates, or somecombination of thesemicro structures  For anon genetic, general term to cover all surfacesfound in deformed metamorphic rocksusetheword foliation.  somegeologist usetheword foliation in amorerestricted senceto refer only to surfacesproduced by deformation and metamorphism.  Theword lineation isused to describeany linear structurethat occurs repetitively in asampleof rock; for exampleit may refer to to an array of elongatepebblesoriented with thier long dimensionsparallel or it may refer to thelinesof intersection of two foliations. 31-08-2012 22

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 Books:  Bruce.E. Hobbs, Winthrop. D. Means, Pual.F Williams(1976) Out lineof structural geology -Pageno:213-280  Ben.A. Vander Pluijm and Stephen Marshak (2004) Earth Structure– An Introduction to structural geology and Techtonics-2nd edition,-pageno:270-292  CeesW. Passchier Rudolph A.J. Trouw (2005) Micro-Techtonics_ second edition.- Pageno: 67-102  Websites:  www.colby.edu/.../w/.../Lecture%2004%20Foliation%20and%20lineation.ppt  www.geo.arizona.edu/geo3xx/geo304/Foliations_Lineations.pp  www.wou.edu/las/physci/taylor/es406.../TM_chap13_Foliations.pdf  www.globalchange.umich.edu/Ben/.../ppts/11_FoliationsLineations.pdf 31-08-2012 23

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More Related Content

Analysis and interpretation of foliation and lineation

  • 2.  INTRODUCTION  FOLIATION  Foliation Includes  Significanceof Foliation  Primary Foliation  Diagenetic Foliation  Secondary Foliation  Two general typesof foliation:  Relationship of Foliation to Folds  LINEATION  Classification form lineations, Surfacelineations, and mineral lineations  CONCLUSION  REFERENCES 31-08-2012 2
  • 3.  In structural geology the term fabrics mean the arrangement of component featuresof therock.  Fabricsinclude-foliation and leneation  Foliation is any closely-spaced, systematically oriented planar feature that occurs penetratively in a body of rock, and commonly associated with folds.it is a characteristic of tectonites, i.e., rocks formed by deformation which are commonly, but not necessarily, metamorphosed.  Leneation-Leneation isafabric element which can berepresent a line.It can beassociated with other structuressuch asfold, bouldins.It may represent on thesurfaceof therock body and sometimeit reflect thearrangement of themineral grain. 31-08-2012 3
  • 4.  A homogeneously distributed planar structurein arock.  Foliation isacharacteristic of tectonites, i.e., rocksformed by deformation which arecommonly, but not necessarily, metamorphosed.  spatial variation in mineral composition or grain size.  preferred orientation of platy grainsin a matrix without fabric. e.g., micain micaceousquartziteor gneiss.  preferred orientation of grain boundaries of deformed elongategrains./lenticular mineral/grain aggregates.  e.g., elongatequartz or calcite.. 31-08-2012 4
  • 5. 31-08-2012 5 a. Compositional layering b. B.grain size variation c. Closely spaced d. Preferred orientation of grain boundaries e. Preferred orientation of platy minerals f. Combination of a+e this is very common in both sedimentary and metamorphic rocks
  • 6.  Rhythmic bedding in sedimentary rocks  Compositional layering in igneousrocks  planar alignment of sedimentary clasts.  parallel alignment of conglomeratepebbles.  planar alignment of fused clastsin ignimbrite  S-C foliation in metamorphic rocks  Excludesjointsbecausethey arenot sufficiently penetrative. 31-08-2012 6
  • 7. Deformed terrainscommonly haveseveral successivegenerationsof foliation. 1. If thesecan bedistinguished from oneanother by typeand age (cross-cutting relationships, absoluteagedates, and overprinting under microscope), ▪ can help to unravel thetectonic and metamorphic evolution of an area. 1. Foliationscan beused to asreferencestructuresto establish the: ▪ relativegrowth periodsof metamorphic minerals, especially porphyroblasts ▪ deformation phasesin an area. Foliation may be related to folds, however, foliation ismorepenetrativethan related foldsand thereforecan beseen better. 31-08-2012 7
  • 8.  Structures related to the original rock-forming process.  Originated by sedimentary processes such astransport and deposition: ▪ Bedding ▪ preferred orientation of sedimentary clasts  Originated by primary igneous processes such asflow and crystallization: ▪ magmatic layering in igneousrocks ▪ preferred orientation of bubblesand pumicefragments 31-08-2012 8
  • 9.  Formsby diagenetic processessuch ascompaction in sedimentswith detrital mica.  Arealso known asbedding-parallel foliation.  Observed in very low and low-gradepelitic sedimentswhich have undergonelittleor no deformation.  Isdefined by parallel orientation of thin elongatedetrital micagrainswith frayed edges.  Themicasarecommonly subparallel to bedding.  Thepreferred orientation of themicasisdueto their passiverotation.  Diagenetic foliation isnot associated with folds.  It precedestheformation of secondary foliation.  It playsan important rolein development of secondary foliation in pelites. 31-08-2012 9
  • 10.  Formsafter lithification and crystallization of rocks.  Formsby somekind of differentiation processin astressfield.  Iscommonly (sub)parallel to thefold axial plane.  Isrelated to strain (parallel to theXY plane) and deformed features.  Formsasaresult of:  ductiledeformation (by crystal plasticity or cataclastic flow)  metamorphism.  Includes:  cleavage  schistosity  differentiated compositional layering  mylonitic foliation (Sand C) 31-08-2012 10
  • 11.  Cleavage – Traditionally: the property of a rock to split along a regular set of sub- parallel, closely-spaced planes – A more general concept adopted by some geologists is to consider cleavage to be any type of foliation in which the aligned platy phyllosilicates are too fine grained to see individually with the unaided eye Schistosity – A preferred orientation of inequaint mineral grains or grain aggregates produced by metamorphic processes – Aligned minerals are coarse grained enough to see with the unaided eye – The orientation is generally planar, but linear orientations are not excluded 31-08-2012 11
  • 13.  Rock consists of two types of domains:  1. Cleavage domain: ▪ Planar, and havefabric elements subparallel to thetrend of thedomain. ▪ In metapelites, it isrich in micaand other mineralssuch asilmenite, graphite, rutile, apatite, and zircon. 31-08-2012 13 2. Microlithons liebetween cleavagedomains contain fabric elementswith weak or no preferred orientation may contain fabric elementsobliqueto thecleavagedomains. Fabric elements are not homogeneously distributed. The rock is divided into lenses or layers of different composition.
  • 14. Fabric elementsarehomogeneously distributed, to thescaleof grain individual minerals. Consistsof anon-layered homogeneous distribution of platy mineral grainswith apreferred orientation. - mineralsarecommonly micaand amphibole; sometimesquartz, etc. Theterminology isbased on observation under themicroscope. 31-08-2012 14 Fabric elements such as grain shape and size are used to classify continuous foliations. - Continuous Schistosity: grainsdefining thefoliation arevisibleby theunaided eye. - Continuous Cleavage or slaty cleavage: grainsarefiner and need microscope.
  • 15.  Foliation is commonly associated with folds.  Foliation in the hinge zone of a fold is parallel to the axial plane of the fold.  Foliation on the fold limbs may fan around the axial plane  Foliation may be refracted at boundaries between layers of different lithology.  Convergent fan - foliation converges from the convex toward the concave side of the folded layer, e.g., in competent rocks such as sandstone.  Divergent fan - foliation diverges from the convex toward the concave side of the folded layer, e.g., in the less competent rocks such as shale or schist.  Foliation formed by folding should be more steeply inclined than bedding on the fold limbs unless the fold has been overturned. 31-08-2012 15
  • 16.  Leneation isafabric element which can berepresent aline.  Theword lineation isused to describeany lenear structurethat occursrepetitively in asampleof rock  Leneation can beassociated with other structuressuch asfold, bouldins  It may represent on thesurfaceof therock body and sometimeit reflect thearrangement of the mineral grain. 31-08-2012 16
  • 17. 31-08-2012 17 a.Simple linear fabric defined by preferreed orientation of linear bodies b.Combined lineation and foliation defined by prefeered orintation of elongate tabular bodies c.Linear fabrics defined by common axis of intersection of variably oriented, tabular bodies d. Linear fabrics defined by penitrative folding e.Lineation defined by intersection of 2 foliations a.Simple linear fabric defined by preferreed orientation of linear bodies b.Combined lineation and foliation defined by prefeered orintation of elongate tabular bodies c.Linear fabrics defined by common axis of intersection of variably oriented, tabular bodies d. Linear fabrics defined by penitrative folding e.Lineation defined by intersection of 2 foliations
  • 18. Leneation broadly divided into into three categories: form lineations, Surface lineations, and mineral lineations 31-08-2012 18
  • 19.  The hinge of any fold is a linear feature,the folds are might be closely or widely spaced.It is the fold hinges effectively define a rock fabric that can be measured as a fold hinge lineation.  Boudins are tablet-shaped lenses of a relatively rigid lithology, embedded in a weaker matrix, that have collectively undergone layer- parallel stretching 31-08-2012 19
  • 20. ▪ An intersection lineation isalinear fabric element formed by, asthenamesuggests, theintersection of two planar fabric elements. 31-08-2012 20
  • 21.  Fabric element definesthis leneation isthesizeof mineral grain or theclustur of the mineral grain.  Mineral leneation commonly occur in foliation planeof metamorphic rock and in plane of mylonitic foliation.  Thisismainly caused by structing (stress,strain) and generally called structural leneation. 31-08-2012 21 e lineation on a bedding plane. Proterozoic Marinoan Group. Hallett Cove, South Australia. [-35.07
  • 22.  Metamorphic rockstherearecommonly pervasivesurfacesdefined by dis continuities, preferred orientation of inequant minerals, laminar mineral aggregates, or somecombination of thesemicro structures  For anon genetic, general term to cover all surfacesfound in deformed metamorphic rocksusetheword foliation.  somegeologist usetheword foliation in amorerestricted senceto refer only to surfacesproduced by deformation and metamorphism.  Theword lineation isused to describeany linear structurethat occurs repetitively in asampleof rock; for exampleit may refer to to an array of elongatepebblesoriented with thier long dimensionsparallel or it may refer to thelinesof intersection of two foliations. 31-08-2012 22
  • 23.  Books:  Bruce.E. Hobbs, Winthrop. D. Means, Pual.F Williams(1976) Out lineof structural geology -Pageno:213-280  Ben.A. Vander Pluijm and Stephen Marshak (2004) Earth Structure– An Introduction to structural geology and Techtonics-2nd edition,-pageno:270-292  CeesW. Passchier Rudolph A.J. Trouw (2005) Micro-Techtonics_ second edition.- Pageno: 67-102  Websites:  www.colby.edu/.../w/.../Lecture%2004%20Foliation%20and%20lineation.ppt  www.geo.arizona.edu/geo3xx/geo304/Foliations_Lineations.pp  www.wou.edu/las/physci/taylor/es406.../TM_chap13_Foliations.pdf  www.globalchange.umich.edu/Ben/.../ppts/11_FoliationsLineations.pdf 31-08-2012 23