Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                
SlideShare a Scribd company logo

Cleavage

•Download as PPT, PDF•
•
Saad Raja
Saad Raja

This document discusses various types of planar and linear structures in deformed rocks, including cleavage, foliation, folds, and lineations. It defines cleavage as a tendency to split along planes other than bedding, often linked to folding and metamorphism. Foliation refers to the spatial and geometric relationships that make up metamorphic rocks, including the orientation of minerals. Different types of cleavage like slaty, crenulation, and spaced cleavage are described. The relationship between cleavage, bedding, and folds is also explained.

1 of 20
UNIVERSITY OF AZADUNIVERSITY OF AZAD JAMMU AND KASHMIRJAMMU AND KASHMIR MUZAFFARABADMUZAFFARABAD
CLEAVAGE AND FOLIATIONSCLEAVAGE AND FOLIATIONS
CLEAVAGECLEAVAGE A tendency to split along planesA tendency to split along planes other than bedding. Cleavageother than bedding. Cleavage is directly linked to otheris directly linked to other deformation processes-deformation processes- especially folding- andespecially folding- and metamorphism.metamorphism. It can help inIt can help in understanding the foldunderstanding the fold geometry and the physicalgeometry and the physical conditions during deformationconditions during deformation.. It may serve as a conduit forIt may serve as a conduit for ground waterground water
FabricFabric Is used to describe the spatial andIs used to describe the spatial and geometric relationships that makegeometric relationships that make up the rock.up the rock. It includes planar andIt includes planar and linear structures-bedding, cleavage,linear structures-bedding, cleavage, and the orientation of minerals andand the orientation of minerals and their relationship to texturetheir relationship to texture..
Slaty CleavageSlaty Cleavage Is a penetrative structure (occurs in allIs a penetrative structure (occurs in all scale).scale). It consists of parallel grains ofIt consists of parallel grains of thin layer silicates (clay minerals orthin layer silicates (clay minerals or micas) or thin anastomosing subparallelmicas) or thin anastomosing subparallel zones insoluble residues produced byzones insoluble residues produced by pressure solutionpressure solution..
S-surfacesS-surfaces Planar and some curved structures in deformed rocks.Planar and some curved structures in deformed rocks. They include allThey include all cleavages and foliations commonlycleavages and foliations commonly though as penetrative structures. They also includethough as penetrative structures. They also include nontectonic planar structure, beddingnontectonic planar structure, bedding. In areas of. In areas of multiple S-surfaces, a series of subscripts ismultiple S-surfaces, a series of subscripts is assigned bedding being oldest is designated S0, S1 isassigned bedding being oldest is designated S0, S1 is the oldest cleavage (or foliation) and any laterthe oldest cleavage (or foliation) and any later structures are given numerically higher subscripts.structures are given numerically higher subscripts.
Cleavage and Foliation can be divided intoCleavage and Foliation can be divided into ContinuousContinuous :: Cut all the rockCut all the rock mass.mass. Spaced:Spaced: can be resolved into regionscan be resolved into regions of uncleaved rock separated byof uncleaved rock separated by cleavage planes spaced from lesscleavage planes spaced from less than a millimeters to severalthan a millimeters to several centimeters.centimeters. The uncleaved zonesThe uncleaved zones between cleavage surfaces arebetween cleavage surfaces are called microlithonscalled microlithons..
Spaced cleavage is divided intoSpaced cleavage is divided into  Disjunctive (cross-cutting and not related to original layering)Disjunctive (cross-cutting and not related to original layering) Disjunctive cleavage may be divided into:Disjunctive cleavage may be divided into: styloiticstyloitic anastomosinganastomosing roughrough smoothsmooth  Crenulation (which crenulates preexisting layering)Crenulation (which crenulates preexisting layering) Crenulation cleavage may be divided into :Crenulation cleavage may be divided into : discretediscrete zonalzonal Spacing in the different types of cleavage:Spacing in the different types of cleavage: slaty cleavage (continuous)slaty cleavage (continuous) 0.01 mm to less than 1.o mm0.01 mm to less than 1.o mm crenulations cleavagecrenulations cleavage 0.1 mm to 3cm0.1 mm to 3cm Shale usually display more closely spaced cleavage compared to sandstone thatShale usually display more closely spaced cleavage compared to sandstone that shows wide space cleavage (Figs. 17-4 and 17-7)shows wide space cleavage (Figs. 17-4 and 17-7)
Cleavage typesCleavage types Pressure solutionPressure solution produces spaced cleavage by dissolving the most soluble parts of a rockproduces spaced cleavage by dissolving the most soluble parts of a rock mass leaving behind discrete insoluble residues in irregular planar zonesmass leaving behind discrete insoluble residues in irregular planar zones that define cleavage (Fig. 17-8). Spacing of pressure solution rangesthat define cleavage (Fig. 17-8). Spacing of pressure solution ranges from less than a millimeter to more than a centimeter. They may befrom less than a millimeter to more than a centimeter. They may be irregular ( styloitic to anastomsing to rough) to smooth, where rock massirregular ( styloitic to anastomsing to rough) to smooth, where rock mass is more severely deformed.is more severely deformed. Slaty cleavageSlaty cleavage is a planar tectonic structure resulting from parallel orientation of clays,is a planar tectonic structure resulting from parallel orientation of clays, muscovite, and or chlorite. It is penetrative and develop generally inmuscovite, and or chlorite. It is penetrative and develop generally in rocks of fine-grained sedimentary and volcanic rocks, such as shale,rocks of fine-grained sedimentary and volcanic rocks, such as shale, mudstone, siltstone, and tuff.mudstone, siltstone, and tuff. FORMATION OF SLATY CLEAVAGE:FORMATION OF SLATY CLEAVAGE: Folding, Compression, Pressure solution, recrystalliztion and pure and simple shears concepts.Folding, Compression, Pressure solution, recrystalliztion and pure and simple shears concepts.
Crenulation cleavageCrenulation cleavage cleavage marked by small-scale crinkling or crenulation. Most crinkles are spaced and asymmetric, and the short limb becomes usually the cleavage plane. They commonly form by deformation of an earlier cleavage or bedding. FoliationFoliation foliation is a term used to describe all type of cleavage slaty, crenulation and it is used also to describe the planar structure in coarser-grained metamorphic rocks, such as schist and gneiss where planar orientation of at least one mineral dominates the fabric (parallel of mica, amphibole, and flatten of quartz grains). Schistosity refers to foliation in schistose. Foliation is easily recognized if there is an alternate of quartz and feldsparsFoliation is easily recognized if there is an alternate of quartz and feldspars with mica and amphibole.with mica and amphibole. Cleavage typesCleavage types
Metamorphic differentiation:Metamorphic differentiation: formation of new layering by recrystallization or pressureformation of new layering by recrystallization or pressure solution. It is the production of new minerals with newsolution. It is the production of new minerals with new orientationorientation. Differential layeringDifferential layering the foliation that is produced during metamorphism andthe foliation that is produced during metamorphism and recrystallization.recrystallization. At high temperature and pressure this process will be enhanced with processes andAt high temperature and pressure this process will be enhanced with processes and gniessic banding may be produced.gniessic banding may be produced. Crenulations and spaced slaty cleavage may produce differential layering at lowCrenulations and spaced slaty cleavage may produce differential layering at low temperature and pressure.temperature and pressure. Cleavage typesCleavage types
CLEAVAGE BEDDING RELATIONSHIPCLEAVAGE BEDDING RELATIONSHIP The angular relationship between cleavage andThe angular relationship between cleavage and bedding can be used to determine whether one isbedding can be used to determine whether one is observing the upright or the overturned limb of aobserving the upright or the overturned limb of a fold.fold. If bedding dips less steeply (lower angle but sameIf bedding dips less steeply (lower angle but same direction as cleavage) the rock will be on uprightdirection as cleavage) the rock will be on upright limb.limb. Care should be taken regarding the fold axis andCare should be taken regarding the fold axis and timing of cleavage.timing of cleavage.
CLEAVAGE REFRACTIONCLEAVAGE REFRACTION  Refraction of cleavage from layer to layer occurs where the texture and composition-ductility- vary from layer to layer in rocks. The angle between cleavage and bedding changes or refracts as the cleavage passes from one layer to another (Fig. 17- 16)  Most slaty cleavage forms parallel to axial surfaces in folds but may be displaced or fanned with respect to the hinge as folding proceeds (Fig. 17-17)
LINEAR STRUCTURESLINEAR STRUCTURES Any structure that can be expressed as a real or imaginary line is linear structure or lineation. Lineament is a topographic feature consisting of straight or aligned surficial features such as valleys and ridges.
Non-penetrative linear structuresNon-penetrative linear structures Non-penetrative linear structures:Non-penetrative linear structures: Slickenlines:Slickenlines: are the direct result ofare the direct result of frictional sliding.frictional sliding. Slinckensides:Slinckensides: refer to the entirerefer to the entire movement surface develop on the faultmovement surface develop on the fault surface, bedding, and foliation.surface, bedding, and foliation. Slinkenfibers:Slinkenfibers: fibrous crystals of calcite,fibrous crystals of calcite, quartz, chlorite or iron oxides wherequartz, chlorite or iron oxides where their long axes are oriented in thetheir long axes are oriented in the direction of movement.direction of movement.
Penetrative linear structuresPenetrative linear structures Penetrative linear structures:Penetrative linear structures: Intersection lineation (two cleavage or foliation planes) Mineral lineationMineral lineation (alignment of grain aggregates of mica, amphibole or feldspars) Pressure shadow:Pressure shadow: of quartz, muscovite, chlorite, magnetite on either side of single crystal of pyrite Rotated minerals Rods: rodding or grain aggregates of one or more minerals such as quartz, feldspars and mica (it is common in ductile shear zones) Natural strain ellipsoids : long axes of pebbles, boulders, vesicles and reduction spots. Mullions: form at boundaries between differing rock types. Boudinage: consists of lenticular segments of layer that has been pulled apart and flattened (layer been segmented is less ductile than enclosing). Shape of boudins is affected by the degree of contrast between the two rocks. Large contrast produces boudins with sharp edges, and small contrast produces rounded boudins. Boudins can produce under conditions of either ductile or brittle. Under brittle condition most boudins are angler and space between them is filled with less-competent rock
Type of BoudinsType of Boudins 1) Ordinary boudinage:1) Ordinary boudinage: consists of segmented, sausage shaped of a singleconsists of segmented, sausage shaped of a single layer in which the lenticular segments parallel onelayer in which the lenticular segments parallel one another. It results from extension of the layer in aanother. It results from extension of the layer in a single direction.single direction. 2) Chocolate-block (chocolate tablet) boudinage2) Chocolate-block (chocolate tablet) boudinage:: It is produced if layer-parallel extension hasIt is produced if layer-parallel extension has occurred in two directions, the resultingoccurred in two directions, the resulting boudinage consists of a series of three-boudinage consists of a series of three- dimensional blocks.dimensional blocks.
Importance ofImportance of BoudinsBoudins  They yield informationThey yield information aboutabout strain, shear sense andstrain, shear sense and difference in competencedifference in competence..  The neck lineThe neck line of the boudin isof the boudin is the lineation and isthe lineation and is commonly oriented parallelcommonly oriented parallel to the fold axesto the fold axes..  Boundinage is frequentlyBoundinage is frequently seen in theseen in the limbs of the folds,limbs of the folds, where most flattening andwhere most flattening and layer-parallellayer-parallel extensionextension occurs.occurs.
LINEATION AS SHEAR-SENSE INDICATORSLINEATION AS SHEAR-SENSE INDICATORS  Slickensides directly indicateSlickensides directly indicate movement sense by the directionmovement sense by the direction of their lines and steps.of their lines and steps.  Boudins indicateBoudins indicate the extensionthe extension direction.direction.  Mineral lineationsMineral lineations yields senseyields sense of shear if the linear mineral isof shear if the linear mineral is segmented in the movementsegmented in the movement direction.direction.  Rotated minerals are shear-Rotated minerals are shear- sensesense indicators-the direction ofindicators-the direction of movement is perpendicular tomovement is perpendicular to the lineation (rotation axis)the lineation (rotation axis)
FOLDS AND LINEATIONSFOLDS AND LINEATIONS  Intersection lineations tend to parallel foldIntersection lineations tend to parallel fold axesaxes..  Mullions and Boudin necks generallyMullions and Boudin necks generally parallel the fold axes.parallel the fold axes.  Mineral-elongation lineations sometimesMineral-elongation lineations sometimes parallel fold axes and are sometimesparallel fold axes and are sometimes oriented oblique to normal to fold axes.oriented oblique to normal to fold axes.  Deformed lineations are strain markers thatDeformed lineations are strain markers that can help to reveal the later deformationcan help to reveal the later deformation..

More Related Content

Cleavage

  • 1. UNIVERSITY OF AZADUNIVERSITY OF AZAD JAMMU AND KASHMIRJAMMU AND KASHMIR MUZAFFARABADMUZAFFARABAD
  • 3. CLEAVAGECLEAVAGE A tendency to split along planesA tendency to split along planes other than bedding. Cleavageother than bedding. Cleavage is directly linked to otheris directly linked to other deformation processes-deformation processes- especially folding- andespecially folding- and metamorphism.metamorphism. It can help inIt can help in understanding the foldunderstanding the fold geometry and the physicalgeometry and the physical conditions during deformationconditions during deformation.. It may serve as a conduit forIt may serve as a conduit for ground waterground water
  • 4. FabricFabric Is used to describe the spatial andIs used to describe the spatial and geometric relationships that makegeometric relationships that make up the rock.up the rock. It includes planar andIt includes planar and linear structures-bedding, cleavage,linear structures-bedding, cleavage, and the orientation of minerals andand the orientation of minerals and their relationship to texturetheir relationship to texture..
  • 5. Slaty CleavageSlaty Cleavage Is a penetrative structure (occurs in allIs a penetrative structure (occurs in all scale).scale). It consists of parallel grains ofIt consists of parallel grains of thin layer silicates (clay minerals orthin layer silicates (clay minerals or micas) or thin anastomosing subparallelmicas) or thin anastomosing subparallel zones insoluble residues produced byzones insoluble residues produced by pressure solutionpressure solution..
  • 6. S-surfacesS-surfaces Planar and some curved structures in deformed rocks.Planar and some curved structures in deformed rocks. They include allThey include all cleavages and foliations commonlycleavages and foliations commonly though as penetrative structures. They also includethough as penetrative structures. They also include nontectonic planar structure, beddingnontectonic planar structure, bedding. In areas of. In areas of multiple S-surfaces, a series of subscripts ismultiple S-surfaces, a series of subscripts is assigned bedding being oldest is designated S0, S1 isassigned bedding being oldest is designated S0, S1 is the oldest cleavage (or foliation) and any laterthe oldest cleavage (or foliation) and any later structures are given numerically higher subscripts.structures are given numerically higher subscripts.
  • 7. Cleavage and Foliation can be divided intoCleavage and Foliation can be divided into ContinuousContinuous :: Cut all the rockCut all the rock mass.mass. Spaced:Spaced: can be resolved into regionscan be resolved into regions of uncleaved rock separated byof uncleaved rock separated by cleavage planes spaced from lesscleavage planes spaced from less than a millimeters to severalthan a millimeters to several centimeters.centimeters. The uncleaved zonesThe uncleaved zones between cleavage surfaces arebetween cleavage surfaces are called microlithonscalled microlithons..
  • 8. Spaced cleavage is divided intoSpaced cleavage is divided into  Disjunctive (cross-cutting and not related to original layering)Disjunctive (cross-cutting and not related to original layering) Disjunctive cleavage may be divided into:Disjunctive cleavage may be divided into: styloiticstyloitic anastomosinganastomosing roughrough smoothsmooth  Crenulation (which crenulates preexisting layering)Crenulation (which crenulates preexisting layering) Crenulation cleavage may be divided into :Crenulation cleavage may be divided into : discretediscrete zonalzonal Spacing in the different types of cleavage:Spacing in the different types of cleavage: slaty cleavage (continuous)slaty cleavage (continuous) 0.01 mm to less than 1.o mm0.01 mm to less than 1.o mm crenulations cleavagecrenulations cleavage 0.1 mm to 3cm0.1 mm to 3cm Shale usually display more closely spaced cleavage compared to sandstone thatShale usually display more closely spaced cleavage compared to sandstone that shows wide space cleavage (Figs. 17-4 and 17-7)shows wide space cleavage (Figs. 17-4 and 17-7)
  • 9. Cleavage typesCleavage types Pressure solutionPressure solution produces spaced cleavage by dissolving the most soluble parts of a rockproduces spaced cleavage by dissolving the most soluble parts of a rock mass leaving behind discrete insoluble residues in irregular planar zonesmass leaving behind discrete insoluble residues in irregular planar zones that define cleavage (Fig. 17-8). Spacing of pressure solution rangesthat define cleavage (Fig. 17-8). Spacing of pressure solution ranges from less than a millimeter to more than a centimeter. They may befrom less than a millimeter to more than a centimeter. They may be irregular ( styloitic to anastomsing to rough) to smooth, where rock massirregular ( styloitic to anastomsing to rough) to smooth, where rock mass is more severely deformed.is more severely deformed. Slaty cleavageSlaty cleavage is a planar tectonic structure resulting from parallel orientation of clays,is a planar tectonic structure resulting from parallel orientation of clays, muscovite, and or chlorite. It is penetrative and develop generally inmuscovite, and or chlorite. It is penetrative and develop generally in rocks of fine-grained sedimentary and volcanic rocks, such as shale,rocks of fine-grained sedimentary and volcanic rocks, such as shale, mudstone, siltstone, and tuff.mudstone, siltstone, and tuff. FORMATION OF SLATY CLEAVAGE:FORMATION OF SLATY CLEAVAGE: Folding, Compression, Pressure solution, recrystalliztion and pure and simple shears concepts.Folding, Compression, Pressure solution, recrystalliztion and pure and simple shears concepts.
  • 10. Crenulation cleavageCrenulation cleavage cleavage marked by small-scale crinkling or crenulation. Most crinkles are spaced and asymmetric, and the short limb becomes usually the cleavage plane. They commonly form by deformation of an earlier cleavage or bedding. FoliationFoliation foliation is a term used to describe all type of cleavage slaty, crenulation and it is used also to describe the planar structure in coarser-grained metamorphic rocks, such as schist and gneiss where planar orientation of at least one mineral dominates the fabric (parallel of mica, amphibole, and flatten of quartz grains). Schistosity refers to foliation in schistose. Foliation is easily recognized if there is an alternate of quartz and feldsparsFoliation is easily recognized if there is an alternate of quartz and feldspars with mica and amphibole.with mica and amphibole. Cleavage typesCleavage types
  • 11. Metamorphic differentiation:Metamorphic differentiation: formation of new layering by recrystallization or pressureformation of new layering by recrystallization or pressure solution. It is the production of new minerals with newsolution. It is the production of new minerals with new orientationorientation. Differential layeringDifferential layering the foliation that is produced during metamorphism andthe foliation that is produced during metamorphism and recrystallization.recrystallization. At high temperature and pressure this process will be enhanced with processes andAt high temperature and pressure this process will be enhanced with processes and gniessic banding may be produced.gniessic banding may be produced. Crenulations and spaced slaty cleavage may produce differential layering at lowCrenulations and spaced slaty cleavage may produce differential layering at low temperature and pressure.temperature and pressure. Cleavage typesCleavage types
  • 12. CLEAVAGE BEDDING RELATIONSHIPCLEAVAGE BEDDING RELATIONSHIP The angular relationship between cleavage andThe angular relationship between cleavage and bedding can be used to determine whether one isbedding can be used to determine whether one is observing the upright or the overturned limb of aobserving the upright or the overturned limb of a fold.fold. If bedding dips less steeply (lower angle but sameIf bedding dips less steeply (lower angle but same direction as cleavage) the rock will be on uprightdirection as cleavage) the rock will be on upright limb.limb. Care should be taken regarding the fold axis andCare should be taken regarding the fold axis and timing of cleavage.timing of cleavage.
  • 13. CLEAVAGE REFRACTIONCLEAVAGE REFRACTION  Refraction of cleavage from layer to layer occurs where the texture and composition-ductility- vary from layer to layer in rocks. The angle between cleavage and bedding changes or refracts as the cleavage passes from one layer to another (Fig. 17- 16)  Most slaty cleavage forms parallel to axial surfaces in folds but may be displaced or fanned with respect to the hinge as folding proceeds (Fig. 17-17)
  • 14. LINEAR STRUCTURESLINEAR STRUCTURES Any structure that can be expressed as a real or imaginary line is linear structure or lineation. Lineament is a topographic feature consisting of straight or aligned surficial features such as valleys and ridges.
  • 15. Non-penetrative linear structuresNon-penetrative linear structures Non-penetrative linear structures:Non-penetrative linear structures: Slickenlines:Slickenlines: are the direct result ofare the direct result of frictional sliding.frictional sliding. Slinckensides:Slinckensides: refer to the entirerefer to the entire movement surface develop on the faultmovement surface develop on the fault surface, bedding, and foliation.surface, bedding, and foliation. Slinkenfibers:Slinkenfibers: fibrous crystals of calcite,fibrous crystals of calcite, quartz, chlorite or iron oxides wherequartz, chlorite or iron oxides where their long axes are oriented in thetheir long axes are oriented in the direction of movement.direction of movement.
  • 16. Penetrative linear structuresPenetrative linear structures Penetrative linear structures:Penetrative linear structures: Intersection lineation (two cleavage or foliation planes) Mineral lineationMineral lineation (alignment of grain aggregates of mica, amphibole or feldspars) Pressure shadow:Pressure shadow: of quartz, muscovite, chlorite, magnetite on either side of single crystal of pyrite Rotated minerals Rods: rodding or grain aggregates of one or more minerals such as quartz, feldspars and mica (it is common in ductile shear zones) Natural strain ellipsoids : long axes of pebbles, boulders, vesicles and reduction spots. Mullions: form at boundaries between differing rock types. Boudinage: consists of lenticular segments of layer that has been pulled apart and flattened (layer been segmented is less ductile than enclosing). Shape of boudins is affected by the degree of contrast between the two rocks. Large contrast produces boudins with sharp edges, and small contrast produces rounded boudins. Boudins can produce under conditions of either ductile or brittle. Under brittle condition most boudins are angler and space between them is filled with less-competent rock
  • 17. Type of BoudinsType of Boudins 1) Ordinary boudinage:1) Ordinary boudinage: consists of segmented, sausage shaped of a singleconsists of segmented, sausage shaped of a single layer in which the lenticular segments parallel onelayer in which the lenticular segments parallel one another. It results from extension of the layer in aanother. It results from extension of the layer in a single direction.single direction. 2) Chocolate-block (chocolate tablet) boudinage2) Chocolate-block (chocolate tablet) boudinage:: It is produced if layer-parallel extension hasIt is produced if layer-parallel extension has occurred in two directions, the resultingoccurred in two directions, the resulting boudinage consists of a series of three-boudinage consists of a series of three- dimensional blocks.dimensional blocks.
  • 18. Importance ofImportance of BoudinsBoudins  They yield informationThey yield information aboutabout strain, shear sense andstrain, shear sense and difference in competencedifference in competence..  The neck lineThe neck line of the boudin isof the boudin is the lineation and isthe lineation and is commonly oriented parallelcommonly oriented parallel to the fold axesto the fold axes..  Boundinage is frequentlyBoundinage is frequently seen in theseen in the limbs of the folds,limbs of the folds, where most flattening andwhere most flattening and layer-parallellayer-parallel extensionextension occurs.occurs.
  • 19. LINEATION AS SHEAR-SENSE INDICATORSLINEATION AS SHEAR-SENSE INDICATORS  Slickensides directly indicateSlickensides directly indicate movement sense by the directionmovement sense by the direction of their lines and steps.of their lines and steps.  Boudins indicateBoudins indicate the extensionthe extension direction.direction.  Mineral lineationsMineral lineations yields senseyields sense of shear if the linear mineral isof shear if the linear mineral is segmented in the movementsegmented in the movement direction.direction.  Rotated minerals are shear-Rotated minerals are shear- sensesense indicators-the direction ofindicators-the direction of movement is perpendicular tomovement is perpendicular to the lineation (rotation axis)the lineation (rotation axis)
  • 20. FOLDS AND LINEATIONSFOLDS AND LINEATIONS  Intersection lineations tend to parallel foldIntersection lineations tend to parallel fold axesaxes..  Mullions and Boudin necks generallyMullions and Boudin necks generally parallel the fold axes.parallel the fold axes.  Mineral-elongation lineations sometimesMineral-elongation lineations sometimes parallel fold axes and are sometimesparallel fold axes and are sometimes oriented oblique to normal to fold axes.oriented oblique to normal to fold axes.  Deformed lineations are strain markers thatDeformed lineations are strain markers that can help to reveal the later deformationcan help to reveal the later deformation..