Cleavage

GEOLOGY

1. UNIVERSITY OF AZAD UNIVERSITY OF AZAD
JAMMU AND KASHMIR JAMMU AND KASHMIR
MUZAFFARABADMUZAFFARABAD

2. CLEAVAGE AND FOLIATIONSCLEAVAGE AND FOLIATIONS

3. CLEAVAGECLEAVAGE
A tendency to split along planes A tendency to split along planes
other than bedding. Cleavage other than bedding. Cleavage
is directly linked to other is directly linked to other
deformation processes-deformation processes-
especially folding- and especially folding- and
metamorphism. metamorphism. It can help in It can help in
understanding the fold understanding the fold
geometry and the physical geometry and the physical
conditions during deformationconditions during deformation. .
It may serve as a conduit for It may serve as a conduit for
ground waterground water

4. FabricFabric
Is used to describe the spatial and Is used to describe the spatial and
geometric relationships that make geometric relationships that make
up the rock. up the rock. It includes planar and It includes planar and
linear structures-bedding, cleavage, linear structures-bedding, cleavage,
and the orientation of minerals and and the orientation of minerals and
their relationship to texturetheir relationship to texture..

5. Slaty CleavageSlaty Cleavage
Is a penetrative structure (occurs in all Is a penetrative structure (occurs in all
scale). scale). It consists of parallel grains of It consists of parallel grains of
thin layer silicates (clay minerals or thin layer silicates (clay minerals or
micas) or thin anastomosing subparallel micas) or thin anastomosing subparallel
zones insoluble residues produced by zones 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 all They include all cleavages and foliations commonly cleavages and foliations commonly
though as penetrative structures. They also include though 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 is multiple S-surfaces, a series of subscripts is
assigned bedding being oldest is designated S0, S1 is assigned bedding being oldest is designated S0, S1 is
the oldest cleavage (or foliation) and any later the 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 rock Cut all the rock
mass.mass.
Spaced:Spaced: can be resolved into regions can be resolved into regions
of uncleaved rock separated by of uncleaved rock separated by
cleavage planes spaced from less cleavage planes spaced from less
than a millimeters to several than a millimeters to several
centimeters. centimeters. The uncleaved zones The uncleaved zones
between cleavage surfaces are between 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
anastomosing anastomosing
rough rough
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 that Shale 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 rock produces spaced cleavage by dissolving the most soluble parts of a rock
mass leaving behind discrete insoluble residues in irregular planar zones mass leaving behind discrete insoluble residues in irregular planar zones
that define cleavage (Fig. 17-8). Spacing of pressure solution ranges that define cleavage (Fig. 17-8). Spacing of pressure solution ranges
from less than a millimeter to more than a centimeter. They may be from less than a millimeter to more than a centimeter. They may be
irregular ( styloitic to anastomsing to rough) to smooth, where rock mass irregular ( 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 in muscovite, 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 feldspars Foliation 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 pressure formation of new layering by recrystallization or pressure
solution. It is the production of new minerals with new solution. It is the production of new minerals with new
orientationorientation.

Differential layeringDifferential layering
the foliation that is produced during metamorphism and the foliation that is produced during metamorphism and
recrystallization.recrystallization.
At high temperature and pressure this process will be enhanced with processes and At 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 low Crenulations 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 and The angular relationship between cleavage and
bedding can be used to determine whether one is bedding can be used to determine whether one is
observing the upright or the overturned limb of a observing the upright or the overturned limb of a
fold.fold.
If bedding dips less steeply (lower angle but same If bedding dips less steeply (lower angle but same
direction as cleavage) the rock will be on upright direction as cleavage) the rock will be on upright
limb.limb.
Care should be taken regarding the fold axis and Care 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 of are the direct result of
frictional sliding.frictional sliding.
Slinckensides:Slinckensides: refer to the entire refer to the entire
movement surface develop on the fault movement 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 where quartz, chlorite or iron oxides where
their long axes are oriented in the their 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 single consists of segmented, sausage shaped of a single
layer in which the lenticular segments parallel one layer in which the lenticular segments parallel one
another. It results from extension of the layer in a another. 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 has It is produced if layer-parallel extension has
occurred in two directions, the resulting occurred 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 of Importance of
BoudinsBoudins
They yield information They yield information about about
strain, shear sense and strain, shear sense and
difference in competencedifference in competence..
The neck line The neck line of the boudin is of the boudin is
the lineation and is the lineation and is
commonly oriented parallel commonly oriented parallel
to the fold axesto the fold axes..
Boundinage is frequently Boundinage is frequently
seen in the seen in the limbs of the folds, limbs of the folds,
where most flattening and where most flattening and
layer-parallellayer-parallel extension extension
occurs.occurs.

19. LINEATION AS SHEAR-SENSE INDICATORSLINEATION AS SHEAR-SENSE INDICATORS
Slickensides directly indicateSlickensides directly indicate
movement sense by the direction movement sense by the direction
of their lines and steps.of their lines and steps.
Boudins indicateBoudins indicate the extension the extension
direction.direction.
Mineral lineationsMineral lineations yields sense yields sense
of shear if the linear mineral is of shear if the linear mineral is
segmented in the movement segmented in the movement
direction.direction.
Rotated minerals are shear-Rotated minerals are shear-
sensesense indicators-the direction of indicators-the direction of
movement is perpendicular to movement is perpendicular to
the lineation (rotation axis)the lineation (rotation axis)

20. FOLDS AND LINEATIONSFOLDS AND LINEATIONS
Intersection lineations tend to parallel fold Intersection lineations tend to parallel fold
axesaxes..
Mullions and Boudin necks generally Mullions and Boudin necks generally
parallel the fold axes.parallel the fold axes.
Mineral-elongation lineations sometimes Mineral-elongation lineations sometimes
parallel fold axes and are sometimes parallel fold axes and are sometimes
oriented oblique to normal to fold axes.oriented oblique to normal to fold axes.
Deformed lineations are strain markers that Deformed lineations are strain markers that
can help to reveal the later deformationcan help to reveal the later deformation..