The document discusses the principles of structural geology, distinguishing between non-tectonic and tectonic structures, and provides explanations of various geological terms such as micro-structure, fabric, foliation, and lineation. It elaborates on primary structures, including bedding and preferred orientations in igneous and sedimentary rocks, as well as secondary structures that arise from deformation under temperature and pressure. Additionally, it categorizes different types of foliation based on their characteristics and formation processes.

1. Structural Geology
By: Ahmed Essam

2. Principles
▰ Non-Tectonic structures:
Also called primary structures
which formed without the
influence of any tectonic
forces.
▰ Tectonic Structures:
A l s o c a l l e d s e c o n d a r y
structures which formed due to
tectonic movements and
activities.
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3. Some Basic concepts
▰ Structure: the geometric
form or shape in rocks with
s c a l e r a n g e f r o m
m i c r o s c o p i c t o l a r g e
regional scale.
▰ T e x t u r e : p r e f e r e d
o r i e n t a t i o n o f
crystallographic axes in 3
dimensions.
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4. Some Basic Concipts
▰ Mico-structure: small scale
arrangement of geometric
forms of minerals within a
rock usually formed due to
external forces or extreme
conditions.
▰ F a b r i c : a g e o m e t r i c
c o n f i g u r a t i o n a n d
a r r a n g e m e n t o f r o c k
elements or components
large enough to be seen in
many samples.
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5. Some Basic Concipts
▰ Foliation: a general term
for any planner fabric in a
rock.
▰ Lineation: a general term to
describe any repeated
a l i g n m e n t o f l i n e a r
elements in a rock.
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6. Foliation Vs. Lineation
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7. Some Basic Concipts
▰ Cleavage: a secondary
fabric element formed
under low temperature
conditions which depends
on rock tendency to split
along planes.
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8. Primary Structure : Foliation
▰ B e d d i n g : t h i s w o r d
indicates a sedimentary
origin which in the original
states sedimentary rocks
are formed and found in a
horizontal pattern not
affected by any tectonic
forces.
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9. Primary Structure : Foliation
▰ Prefered orientation of
Bubbles: characterizes
some types of igneous
extrusive rocks especially "
Pumice fragments ".
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10. Primary Structure : Foliation
▰ Prefered orientation of
clasts: usually charactrizes
clastic sedimentary rocks
which oriantation occurs
d u e t o s e d i m e n t a r y
processes during deposition.
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11. Primary Structure : Foliation
▰ M a g m a t i c l a y e r i n g :
characterizes cumulate
magmatic rocks.
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12. Secondary Structure : Foliation
▰ Secondary foliation: this
type of structures forms
under faverable conditions
of temperature or pressure
o r b o t h , d u e t o s u c h
deformation processes
some mineralogical and
geometric changes may
o c c u r a n d e v e n n e w
minerals may grow.
▰ Secondary foliation usually
divided into to main types:
A. Continuous.
B. Spaced.
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13. Secondary Structure : Foliation
▰ Spaced Foliation:
A. Disjunctive Cleavage.
1. Styolitic.
2. Anastomosing.
3. Rough.
4. Smooth.
A. Crenulation Cleavage.
▰ Continuous Foliation:
1. Pencil Cleavage.
2. Slaty Cleavage.
3. Phyllite structure.
4. Schistosity.
5. Gneissic layering and Migmatization.
6. Mylonitic Foliation.
7. Flattened pebbles. 13
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14. Secondary Structure : Foliation
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15. Spaced Foliation : Disjunctive
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16. Disjunctive : Styolitic
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17. Disjunctive : Anastomosing
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18. Spaced Foliation : Crenulation
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19. Morphological Classification
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20. Continuous Foliation
▰ P e n c i l s t r u c t u r e :
characterizes fine grained
sedimentary rocks like
shales and mudstones
which breaks into elongate
pencil-like shards.
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21. Continuous Foliation
▰ S l a t y c l e a v a g e :
characterizes very low
g r a d e r e g i o n a l
metamorphic rocks which
consists of parallel grains
of chay minerals like
chlorite or mica forming
thin layers.
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22. Pencil Vs. Slaty Cleavage
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23. Continuous Foliation
▰ P h y l l i t i c s t r u c t u r e :
characterizes low grade
metamorphic rocks which
is a continuous cleavage
with a distinctive silky
luster.
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24. Continuous Foliation
▰ Schistosity: characterizes
l o w t o m e d i u m g r a d e
m e t a m o r p h i c r o c k s ,
shcistosity tends to be wavy
as mica curves around the
large crystals.
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25. Continuous Foliation
▰ Gneissic layering and
Migmatization: formed due
to recrystallization of
igneous or sedimentary
rocks during medium, high
a n d v e r y h i g h g r a d e
metamorphism.
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26. Contunuous Foliation
▰ F l a t t e n e d - p e b b l e s :
c h a r a c t e r i z e s
m e t a m o r p h o s e d
c o n g l o m e r a t e s a n d
pyroclastic rocks which
contain pancake-shaped
pebbles arranged parallel to
each other.
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27. Continuous Foliation
▰ M y l o n i t i c F o l i a t i o n :
characterized by grain sizes
have been reduced as a
result of intensive shearing
as ductilely deformed rocks
by the accumulation of
large shear strain in ductile
fault zones.
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28. Mylonite Classification
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29. Thanks
E-mail: geo.ahmedessam@gmail.com
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