Structural geology - Lineation and foliation

1. Lineation and Foliation

2. Contents
•Introduction
•Lineation
Slickenside Straie
 Intersection
 Mineral
 Crenulations
 Stretching
•Foliation
Fracture cleavage
Crenulation cleavage
Slaty cleavage
Schistosity
•Conclusion
•References

3. Introduction

4. Tectonites: Rocks that are pervaded
by foliation and or lineation- flowed
in solid state
Schistosity (foliation) only due to
flattening- no lineation.
L: Lineation only, due to unidirectional
stretching or constriction.
LS: Foliation and Lineation, related
to non coaxial strain- shearing.

5. Lineation
• The word lineation is used to describe any linear structure that
occurs repetitively in a sample of rock; for example,
 it may refer to an array of elongate pebbles, oriented with their
long dimensions mutually parallel, or
it may refer to the lines of intersection of two foliation.
Diorite gneiss

6. Contd..
• Lineation may be defined in a more precise way as any linear
fabric element; it may be primary igneous or sedimentary
structure or a secondary related to deformation
• Lineation are ubiquitous in deformed rocks and is common for
more than one lineation to be visible on a given foliation plane.

7. Origin of lineation
• In the period 1935 to 1960 lineations were used, more or less
indiscriminately, as indicators of “direction of tectonic
transport.”
• The precise meaning of this term was always obscure; to some
it was synonymous with the direction of maximum finite
extension in a deformed rock mass, to others, the “direction of
tectonic transport” was the direction that one rock mass has
been displaced relative to another.
• some writer believed that lineations were always parallel to
the direction of tectonic transport; others believed lineations
were always normal to this direction and others again believed
that they could be at any angle.

8. •Types of lineation
 Slickenside Striae
 Intersection
 Mineral
 Crenulations
 Stretching

9. Slickenside striae
• Slickenside striae are common linear structure in many rocks
but they are not generally a penetrative features and therefore
not a fabric element.
• a slickenside is a smoothly polished surface caused by frictional
movement between rocks along the two sides of a fault. This
surface is normally striated in the direction of movement. The
plane may be coated by mineral fibres that grew during the
fault movement, known as slickenfibres, which also show the
direction of displacement.
• How slickenside is form
and show sense of
movement on a fault

10. Contd..
Slickenside on a sample of dextral slickenside of pyrite
sandstone

11. Intersection
• Intersection of two planar features- an "apparent" lineation in
that there is no fabric that is linear.
• e.g., intersection between cleavage and planar surface

12. Mineral lineation
• Mineral lineation can be defined by the preferred dimensional
orientation of inequant grains or by elongate mineral
aggregates
Hornblende lineation in orthogeiness

13. Crenulations
• Crenulation lineation: Intersection between fold hinges and
foliation

14. Stretching lineation
• elongation of minerals due to "stretching" deformation

15. Contd..
Stretched
calcite

16. Foliation
• Foliation in geology refers to repetitive layering
in metamorphic rocks. Each layer may be as thin as a sheet of
paper, or over a meter in thickness. The word comes from the
Latin folium, meaning "leaf", and refers to the sheet-like planar
structure.It is caused by shearing forces (pressures pushing
different sections of the rock in different directions),
or differential pressure (higher pressure from one direction
than in others)
• foliation is any penetrative planar fabric present
in metamorphic rocks. Rocks exhibiting foliation include the
standard sequence formed by the prograde
metamorphism of mud rocks; slate, phyllite, schist and gneiss.
• Foliated rock is also known as S-tectonite in sheared rock
masses.

17. Contd..
• Gneiss , foliated metamorphic

18. Contd..
Fabric elements that define foliations. In each case the
foliation is parallel to the top of the block. (a) compositional
banding; (b) parallel discontinuities; (c) elongate mineral
grains; (d)inequant mineral grains

19. Types of foliation
Fracture cleavage
Crenulation cleavage
Slaty cleavage
Schistosity

20. Fracture cleavage
• Fracture cleavage consist of closely spaced microfaults or
fractures that divides the rock into a series of tabular bodies
• Fracture cleavage is generally formed in low and medium
metamorphic grade rocks and is common within sandstone
beds in folded sequences of alternating sandstone and pelites
where the cleavage in the pelites is a crenulation cleavage.

21. Crenulation cleavage
• Crenulation cleavage varies considerably in morphology but the
various forms share one diagnostic feature. In all cases an
earlier foliation, generally defined by preferred orientation of
layer silicates, is folded(crenulated) on a micro scale.
• It may be defined as microfaults developed parallel to the fold
limbs

22. Slaty cleavage
• The word slate originated as a quarryman’s term for fine-
grained rocks that were sufficiently fissile to be split into thin,
planar slabs suitable for roofing.
• slates are typically rich in layer silicates but the term slaty
cleavage is also used to describe foliations in low grade
metamorphic rocks of entirely different composition.

23. Schistosity
• Schistosity is a term used to describe the foliation in rocks that
have a grain size coarse enough to be called schists.
• It is most common in high grade metamorphic rocks but also
occurs in low-grade rocks, particularly in greenschist facies
rocks of retrograde origin.

24. Phyllitic structure is a type of foliation

25. Conclusion
• Lineation is a linear structure that occurs repetitively in a
sample of rock and it may refer to an array of elongate
pebbles, oriented with their long dimensions mutually
parallel, or it may refer to the lines of intersection of two
foliation.
• Some writer believed that lineation were always parallel to
the direction of tectonic transport; others believed lineation
were always normal to this direction and others again
believed that they could be at any angle.

26. Contd..
• Foliation in geology refers to repetitive layering in metamorphic
rocks. Each layer may be as thin as a sheet of paper, or over a
meter in thickness.It is caused by shearing forces (pressures
pushing different sections of the rock in different directions),
or differential pressure (higher pressure from one direction than
in others)
• foliation is any penetrative planar fabric present in metamorphic
rocks. Rocks exhibiting foliation include the standard sequence
formed by the prograde
metamorphism of mudrocks; slate, phyllite, schist and
gneiss.

27. Referances
• Bruce E.hobbs, Winthrop D.means, Paul F.Williams (1976), An
Outline of Structural Geology, John Wiley and Sons, INC. U.S.A.
Pp 213-288
• Marland P.Billings, (2013), Structural Geology, PHI learning
private limited, Delhi. Pp 408-419
• http://en.wikipedia.org/wiki/Lineation_(geology)
• https://www.google.co.in/search?q=image+of+foliation