LINEATION AND TYPES

1. LINEATION AND THEIR TYPES
Department of Geology
Guided By Presented By
Dr. Poonam Bhatnagar Aayushi Parwal
M.Sc. I Semester
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2. CONTENT
Lineation.
Types of lineation.
Form lineation.
Surface lineation.
Mineral lineation.
Form lineation.
1. Fold hinge lineation.
2. Crenulation lineation.
3. Boudins. 2

3. 4. Mullions.
5. Pinch and swell structures.
6. Structural slickenlines.
Surface lineation.
1. Intersection lineation.
2. Slip lineation.
Mineral lineation.
1. Mineral grain lineation.
a. Acicular habit lineation.
b. Elongate grain lineation.
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4. c. Mineral fiber lineation.
2. Polycrystalline mineral lineation.
a. Rods.
b. Stretching minerals.
Usefulness of lineations in structural analysis.
1. Geometrical relation with folds.
2. Geometrical relation with strain.
3. Linear structures indicating slip directions.
Conclusion.
Reference.
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5. LINEATION
Lineation is a word used to describe any linear
structure that occurs repetitively in a sample of
rock. Lineation is almost found in deformed
rocks.
• It may refer to an array of elongate pebbles,
oriented with their long dimensions mutually
parallel.
• It may refer to the lines of intersection of two
foliation.
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6. Lineation in gneiss.
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7. We broadly group lineation into three categories
1. Form lineation.
2. Surface lineation.
3. Mineral lineation.
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8. FORM LINEATION
Form lineation may occur as follow:
Fold hinge lineation.
Crenulation lineation.
Boudins.
Mullions.
Pinch and swell structure.
Structural slickenlines.
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9. FOLD HINGE LINEATION
The hinge of any fold is a linear feature. If folds
are closely spaced, the fold hinges effectively
define a rock fabric that we can measure as fold
hinge lineation. It may be treated as regionally
penetrative lineation.
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10. Fold and crenulation hinges.
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11. CRENULATION LINEATION
Crenulation lineation is defined by the hinge
lines of the microfolds in a crenulated rock.
Crenulation means having a contour with
shallow, rounded projection. They are composed
of numerous millimeter to centimeter- scale fold
hinges of low amplitude fold. For example
Phyllites.
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12. BOUDINS
Boudins are competent rock layers that have
been stretched into segments. They yield
information about strain, shear sense, and
differences in competence. The neck line of a
boudin is the lineation commonly parallel to the
fold axes. The process forming boudins is called
boudinage.
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13. Boudins.
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14. MULLIONS
Those linear structures that are restricted to the
interface between a competent and an
incompetent rock are known as mullions.
Mullion structure in metamorphic rocks is at the
boundary between quartzite and phyllite or
micaschist.
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15. Mullion structure.
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16. PINCH AND SWELL
STRUCTURE
Pinch and swell structures are periodic
oscillations in the thickness of a bed, with the
“pinches” becoming thinner as the amount of
lengthening of the bed increases.
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17. Pinch and swell structure.
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18. Cylindrical Pinch and swell structure.
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19. STRUCTURAL SLICKENLINES
Structural slickenlines are grooves and ridges
that appear on Slickensides, the fine grained
polished surfaces that commonly developed
along faults.
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20. Structural slickenlines.
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21. SURFACE LINEATION
Surface lineation are broadly divided into two
types-
1. Intersection lineation.
2. Slip lineation.
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22. INTERSECTION LINEATION
An intersection lineation is a linear fabric
element formed by the intersection of two
planar fabric elements. It is also known as
bedding- cleavage intersection. Since it is a
combination of bedding and cleavage.
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23. Intersection lineation.
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24. Intersection of a foliation and a
bedding surface.
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25. SLIP LINEATION
Slip lineation form on surfaces that move in
opposite directions. This occurs; for example, on
fault surfaces, but also at the interface between
beds in flexural slip folds. Slip lineation are of
two types-
1. Groove lineations, formed by plowing of
surface irregularities.
2. Fiber lineations, that are formed when vein
mineral fibers precipitate along a sliding
surface.
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26. Slip lineation.
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27. MINERAL LINEATION
Mineral lineation consists of a preferred
orientation of either single elongate mineral
grains or elongated polycrystalline aggregates.
Mineral lineation can be classified into two
types-
1. Mineral grain lineation.
2. Polycrystalline mineral lineation.
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28. Mineral lineation in Serpentinite.
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29. MINERAL GRAIN LINEATION
Mineral grain lineation are formed by the
parallel alignment of mineral grains. Three types
of mineral grain lineations commonly exists in
rocks and are formed respectively by acicular
minerals, by elongate mineral grains and by
mineral fibers.
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30. ACICULAR HABIT LINEATION
Some mineral grains, such as amphiboles or
sillimanite, naturally grow with a acicular habit.
If their long axes have a preferred orientation,
such minerals define an acicular habit lineation.
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31. ELONGATE GRAIN LINEATION
Under some conditions, elongate grain
lineations may form in a rock by deformation of
pre- existing equant mineral grains into aligned
elongate forms.
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32. MINERAL FIBER LINEATION
Mineral fiber lineations are formed by very
elongate crystal grains of a particular mineral,
commonly quartz, calcite etc.
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33. Mineral fiber lineation.
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34. POLYCRYSTALLINE MINERAL
LINEATION
Polycrystalline mineral lineation are formed by
the preferred orientation of elongate clusters of
grain of a particular mineral measuring atleast a
few grains in diameter.
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35. RODS
Rods are polycrystalline mineral lineation
formed by rod-shaped concentrations of a
particular mineral, commonly quartz. The rods
may appear in cross-section to be isolated
cylindrical masses that have been boudinaged.
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36. Quartz rod lineation.
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37. STRETCHING LINEATION
Stretching lineations are formed by shearing of
rocks during assymetrical deformation of a rock
mass. This lineation is formed in deformed
metamorphic rocks. Stretching lineation is a
type of mineral lineation.
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38. Stretching lineation in quartzite
conglomerate. 38

39. USEFULNESS OF LINEATIONS
IN STRUCTURAL ANALYSIS
There are generally different types of lineation
in a metamorphic terrain. Their orientations
should be separately recorded during structural
mapping. Even the same rock may have different
types of lineations.
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40. GEOMETRCAL RELATION
WITH FOLDS
The intersection of bedding and axial plane
cleavage is always parallel to the axis of folds
which develop on the bedding. Linear structure
can be utilised to determine the orientation of
the fold axis only if their geometrical relations
with the folds can be clearly established.
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41. GEOMETRICAL RELATION
WITH STRAIN
The pressure shadow lineation is parallel to the
direction of maximum stretching in the rocks.
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42. Pressure- shadow lineation.
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43. LINEAR STRUCTURES
INDICATING SLIP DIRECTION
The striations on slickensides are parallel to the
direction of fault movement. The movement on
a fault may take place over a long period of time
and the direction of movement may change
during this period. The striations on slickensides
are generally parallel to the last phase of the
fault movement.
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44. CONCLUSION
• Lineation is a linear fabric element.
• “Subparallel to parallel alignment of elongate,
linear fabric elements in a rock body.
Commonly penetrative at the outcrop and/ or
hand sample scales of observation.”
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45. REFERENCE
• Robert J. Twiss, Eldridge M. Moores-Structural
geology (Second Edition).
• S. K. Ghosh. -Structural geology
• Haakon Fossen- Structural geology
• Ben A. Van Der Pluijm, Stephen Marshak-Earth
Structure (Second Edition).
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46. THANK YOU
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