Cleavage and its
application
010021-32 chenjianye
Classification and nomenture of
cleavage.
Continuous cleavage
Slaty cleavage
Phyllitic structures
Chisttosity
Disjunctive cleavage
Crenulation cleavage
Discrete crenulation cleavage
Zonal crenulation cleavage
Spaced cleavage
Huge slaty cleavage
Two types of crenulation cleavage
Discrete crenulation
“∫” shape
Zonal crenulation
Transition from the discrete crenulation
cleavage to zonal crenulation cleavage
The faultlike space cleavage
Photomicrograph of
Micrograph
spaced
cleavage
Scanning electon micrograph
of ofspace
cleavage
spaced cleavage
200μm
20μm
Fabrics in cleavage
The fabrics dominal structure, a kind of structural
lamination composed of alternating
cleavage domains and microlithon domains
Cleavage domains are subparallel, mica rich
lamination, within which the original host rock
has been strongly rearranged or partial
removed ;
Microlithon is almost the original rock.
.1.Excellent example of domainal structure, the cleavage domains are the
dark ,fine-grained micaceous zones. The microlithon domains are the
light-colored, lamination of quartz and mica.
2. In section ,oriented micas comprise cleavage domains .the cleavage
domains separate microlithon domains of quartz feldspar,and mica.
Pressure solution --- the
key origin of cleavage
As the figure shows, randomly
oriented minerals can
become dimensionally
aligned by virtue of
preferential grain size
reduction at right angles to
the direction of greatest
shortening due to the
pressure solution .
The using of cleavage
1. Using the geometric relationship of
cleavage and folds.
2. Using the dissolution removed of fossils.
3. Using geometric relationship of
cleavage to shearing.
4. Using of insoluble beds.
5. Using offset bedding.
6. Using of the stylolites.
1. Geometric relationship of
cleavage and folds
Ordinarily cleavage
surface are parallel,
and symmetrically
about the axial
surface. This kind of
cleavage is called
axial plane
cleavage.
What can we know if we see this in
the field?
Could the form of the fold be this ?
A good fit
2.Using the relationship of
cleavage and shearing
Cleavage
domains
Strain ellipse in the cleavage domains
S3
S1
S1
S3
3. Using the dissolution
removed of fossils
If we see the cleavage with partial soluble
fossils, we can calculate extension and
stretch of the rock.
L0
At first, measure
the length of the
rock--- L0.
Then reconstruct the original shape,
and measure the length----L1.
L
L11
E = (L1- L0)/ L0
S= L1/ L0
4. The using of insoluble beds
Another clear signature of pressure solution origin of
spaced cleavage is the strain response of insoluble
layers . The amount of thrust imbrications and/or fold of
chert layers is proportional to the amount of volume loss.
Different intensity of
development of
cleavage cause the
varied degree of fault
imbrication.
Through the insoluble beds, we can
calculate the S and E of the rocks.
L0 represent the
length now.
L=L1+ L2+ L3+ L4
L3
S = L0 /L
E = (L0 -L)/L
L1
L4
L2
5. Using offset bedding
L
In the pressure solution
cleavage, as we saw in our
second field practice, there is
offset of the layers, through
the offset, we can calculate E
and S of the rock.
θfigure shows, at first,
As the
we identify the cleavage
plane and the distinctive
bedding plane. Through the
cleavage, we can know the
main stress direction which
is perpendicular to the
cleavage plane.
Then we should measure the angle θbetween
the cleavage plane and the bedding plane, and
Then we can calculate
the offset L.
the stretch and the
extension of the rock,
and reconstruct the
original graph as the
θ
right figure shows. L0
represent the length
now.
L
ΔL=L*tg(θ)
E=-ΔL/(L0+ΔL)
S= L0/(L0+ΔL)
6. using of the stylolites
Stylolites surface is a special type of cleavage
that usually develops in carbonate stone or
marble. Stylolites surfaces are perpendicular to
the direction of greatest principal stress.
Stylolites have different types with teeth,
cones,columes shapes, as the following figure
shows. And the teeth, cones and columes are
aligned parallel to the direction of greatest
principal stress.
As the figure shows, series of stylolites have
largely shorten the rocks. we can calculate E and
S through stylolites.
At first, measure the
length of the select
part of rock-- L0,
then measure the
lost along each
stylolites surfaces.
L1
Except for L0, We
should measure the
missing amount of
each section due to
the pressure solution,
that is the distance
between the relative
highest point and the
lowest of the stylolites
along the direction of
greatest principal
strees---L1, L2 , L3.
• E= -( L1+L2+ L3 )/( L1+L2+ L3+ L0)
• S= L0/( L1+L2+ L3+ L0).