Review
? Primary sedimentary structures
? Faults (thrust system,extensional fault system,
strike-slip fault system)
? Joints (tension joints,conjugate joints,en echelon
joints)
? Folding (bending,buckling,flexural slip,
flexural flow,passive folding,kinking)
? Stereographic projection
STEREOGRAPHIC PROJECTION
Plotting normal to a plane 90 ∠ 40
Draw the great circle with attitude 90 ∠ 40,count
90 degree along EW from D’,mark the point P’.
It is the projection of the normal to the plane 90 ∠ 40
Solution for apparent dip from true dip
Bedding 300∠ 40
Solve the apparent dip
along the orientation of 335
degree.
1.Plot the bedding and get the
arc EHF.
2.Mark 335 on the primitive
Circle at point D’
3,Link D’O intersecting at H’
4.Count D’H’ along WE or NS.
It is the apparent dip.
solution for the intersection line of
two planes
1,Plot plane EHF and JHK
2,Link OH and extend it to
the primitive circle at G
3,Count the plunge direction
of G on the primitive circle
and the plunge angle GH
on the WE line
Beta Diagram
Pai diagram
Contouring
STRUCTURAL FABRICS I,
Basic categories of
fabrics
a A random fabric
b A preferred
fabric
c A foliation
d A lineation
Concept of fabric:
The geometric
arrangement of
component features
in rock,seen on a
scale large enough
to include many
samples of each
feature,
Planar fabric
and elements
are parallel to
one another
Linear fabric and the size
in one dimension is
much longer than that in
the other two dimensions
Long axes are aligned
with one another
Long axes are not paral-
lel to one another
(a) (b)
FABRICS,‘PENETRATIVE’ VERSUS ‘SPACED’
Penetrative fabric
Pervasive,affecting all
parts of the rock
Spaced fabric
Non-penetrative,occur
at intervals,separated
by unaffected rock.
Non-penetrative cleavage
is often termed spaced
cleavage
cleavage
A secondary fabric element,formed under
low temperature condition,that imparts on
the rock a tendency to split along a set of
planes.
Slaty cleavage the very pervasive cleavage owing to the
preferred alignment of elongate minerals and grains
(phyllosilicates and quartz grains here)
Spaced cleavage
? Fracture cleavage,a set of closely spaced
fractures
? Crenulation cleavage,a banded structure
produced by microfolding
2mmCleavage domain microlithon
Cleavage domain,consists of phyllosilicates and unsoluble materials
Microlithon,almost the
origional rock
Spaced cleavage
Fracture cleavage:
A set of closely spaced
fractures
Relationship between spaced cleavage(S2) and
slaty cleavage (S1),
Diameter 3mm
Axial plane slaty cleavage
Axial plane cleavage:
cleavage that is parallel
or subparallel to the axial
plane of a fold.
FORMATION OF CLEAVAGES
Solution cleavage,in which differential solution and deposition of the
more soluble minerals in the rock has produced a compositional banding.
Pressure shadow
Stylolites in limestone
DISJUNCTIVE
(pressure solution)
CLEAVAGE
Key Word:
‘Stylolite’
Example of Cleavage
AAxial-plane cleavage
Pressure-solution cleavage
pebble
C Crenulation cleavage
short limbs of
asymmetric crenulations
enriched in micas.
D Shape fabric
foliation,Alignment
of flattened and
elongated pebbles
in a deformed
conglomerate.
Cleavage plane
B
CRENULATION CLEAVAGE
Cross-section viewIntersection Lineation
Spaced cleavage
Crenulation cleavage,A,asymmetric; B,symmetric.
The cleavage is parallel to the axial surface traces of the crenulations
Compositional Layering
Produced by Deformation
A1 Solution cleavage defined
by seams enriched in dark
material,owing to the solution
and redeposition of the light
material elsewhere.A1
A2 close-up
of A1
2mm
B showing dark layers where
material is thought to have
been dissolved.
C Gneissose banding in three
stages of deformation,C1 mafic
areas are recognizable,
C2 gneiss with alternating
lensoid mafic and felsic
components,C3 striped rock
whose origins could not be easily
determined.C1 C3
C2
Mafic and Felsic
Mafic composed dominantly of the
magnesian rockforming silicates; dark
minerals,as usually used,Contrasted
with felsic.
Felsic light-colored minerals,The chief
felsic minerals being quartz,feldspars,
feldspathoids,and muscovite(white mica)
A foliation developed during
folding is often subparallel
to the fold axial surface.
B intense deformation may
cause thinning and rotation
of fold limbs into the plane of
the foliation,ultimately
causing the limb to disappear.
Types of folds thus formed
are intrafolial and rootless
intrafolia folds.
C,D Foliation developed
during folding often has a
simple fan-shaped arrangement
about the axial surface,
C divergent fan;
D convergent fan.
Relationship between folds and foliation
AXIAL PLANE CLEAVAGE
Relationship between cleavage and layer
Relationship between cleavage and folds
Cleavage refraction,angles between cleavage
and bedding are different in different rocks
CLEAVAGE
REFRACTION
CLEAVAGE
REFRACTION
2m
Problems
1,Distinguish between different fabrics,
different cleavages
2,How to determine the competency of
rocks from cleavage refraction?
3,Distinguish between different formation
mechanisms of cleavage
? Primary sedimentary structures
? Faults (thrust system,extensional fault system,
strike-slip fault system)
? Joints (tension joints,conjugate joints,en echelon
joints)
? Folding (bending,buckling,flexural slip,
flexural flow,passive folding,kinking)
? Stereographic projection
STEREOGRAPHIC PROJECTION
Plotting normal to a plane 90 ∠ 40
Draw the great circle with attitude 90 ∠ 40,count
90 degree along EW from D’,mark the point P’.
It is the projection of the normal to the plane 90 ∠ 40
Solution for apparent dip from true dip
Bedding 300∠ 40
Solve the apparent dip
along the orientation of 335
degree.
1.Plot the bedding and get the
arc EHF.
2.Mark 335 on the primitive
Circle at point D’
3,Link D’O intersecting at H’
4.Count D’H’ along WE or NS.
It is the apparent dip.
solution for the intersection line of
two planes
1,Plot plane EHF and JHK
2,Link OH and extend it to
the primitive circle at G
3,Count the plunge direction
of G on the primitive circle
and the plunge angle GH
on the WE line
Beta Diagram
Pai diagram
Contouring
STRUCTURAL FABRICS I,
Basic categories of
fabrics
a A random fabric
b A preferred
fabric
c A foliation
d A lineation
Concept of fabric:
The geometric
arrangement of
component features
in rock,seen on a
scale large enough
to include many
samples of each
feature,
Planar fabric
and elements
are parallel to
one another
Linear fabric and the size
in one dimension is
much longer than that in
the other two dimensions
Long axes are aligned
with one another
Long axes are not paral-
lel to one another
(a) (b)
FABRICS,‘PENETRATIVE’ VERSUS ‘SPACED’
Penetrative fabric
Pervasive,affecting all
parts of the rock
Spaced fabric
Non-penetrative,occur
at intervals,separated
by unaffected rock.
Non-penetrative cleavage
is often termed spaced
cleavage
cleavage
A secondary fabric element,formed under
low temperature condition,that imparts on
the rock a tendency to split along a set of
planes.
Slaty cleavage the very pervasive cleavage owing to the
preferred alignment of elongate minerals and grains
(phyllosilicates and quartz grains here)
Spaced cleavage
? Fracture cleavage,a set of closely spaced
fractures
? Crenulation cleavage,a banded structure
produced by microfolding
2mmCleavage domain microlithon
Cleavage domain,consists of phyllosilicates and unsoluble materials
Microlithon,almost the
origional rock
Spaced cleavage
Fracture cleavage:
A set of closely spaced
fractures
Relationship between spaced cleavage(S2) and
slaty cleavage (S1),
Diameter 3mm
Axial plane slaty cleavage
Axial plane cleavage:
cleavage that is parallel
or subparallel to the axial
plane of a fold.
FORMATION OF CLEAVAGES
Solution cleavage,in which differential solution and deposition of the
more soluble minerals in the rock has produced a compositional banding.
Pressure shadow
Stylolites in limestone
DISJUNCTIVE
(pressure solution)
CLEAVAGE
Key Word:
‘Stylolite’
Example of Cleavage
AAxial-plane cleavage
Pressure-solution cleavage
pebble
C Crenulation cleavage
short limbs of
asymmetric crenulations
enriched in micas.
D Shape fabric
foliation,Alignment
of flattened and
elongated pebbles
in a deformed
conglomerate.
Cleavage plane
B
CRENULATION CLEAVAGE
Cross-section viewIntersection Lineation
Spaced cleavage
Crenulation cleavage,A,asymmetric; B,symmetric.
The cleavage is parallel to the axial surface traces of the crenulations
Compositional Layering
Produced by Deformation
A1 Solution cleavage defined
by seams enriched in dark
material,owing to the solution
and redeposition of the light
material elsewhere.A1
A2 close-up
of A1
2mm
B showing dark layers where
material is thought to have
been dissolved.
C Gneissose banding in three
stages of deformation,C1 mafic
areas are recognizable,
C2 gneiss with alternating
lensoid mafic and felsic
components,C3 striped rock
whose origins could not be easily
determined.C1 C3
C2
Mafic and Felsic
Mafic composed dominantly of the
magnesian rockforming silicates; dark
minerals,as usually used,Contrasted
with felsic.
Felsic light-colored minerals,The chief
felsic minerals being quartz,feldspars,
feldspathoids,and muscovite(white mica)
A foliation developed during
folding is often subparallel
to the fold axial surface.
B intense deformation may
cause thinning and rotation
of fold limbs into the plane of
the foliation,ultimately
causing the limb to disappear.
Types of folds thus formed
are intrafolial and rootless
intrafolia folds.
C,D Foliation developed
during folding often has a
simple fan-shaped arrangement
about the axial surface,
C divergent fan;
D convergent fan.
Relationship between folds and foliation
AXIAL PLANE CLEAVAGE
Relationship between cleavage and layer
Relationship between cleavage and folds
Cleavage refraction,angles between cleavage
and bedding are different in different rocks
CLEAVAGE
REFRACTION
CLEAVAGE
REFRACTION
2m
Problems
1,Distinguish between different fabrics,
different cleavages
2,How to determine the competency of
rocks from cleavage refraction?
3,Distinguish between different formation
mechanisms of cleavage
