Analysis and interpretation of foliation and lineation

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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
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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.
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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..
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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.
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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.
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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
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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.
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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)
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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
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12. Spaced foliation
Continuous foliation
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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.
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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.
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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.
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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.
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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
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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
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20. ▪ An intersection lineation isalinear fabric element
formed by, asthenamesuggests, theintersection of two
planar fabric elements.
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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.
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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.
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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
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24. Thanks
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