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Structural geology : foliation

Ahmed Essam
Ahmed Essam

This presentation discusses briefly the differences between foliation and lineation, showing the main types of primary foliation and secondary foliation and how to identify them.

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Structural Geology By: Ahmed Essam
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. 2 Ahmed Essam Ayad
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. 3 Ahmed Essam Ayad
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. 4 Ahmed Essam Ayad
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. 5 Ahmed Essam Ayad
Foliation Vs. Lineation 6 Ahmed Essam Ayad
Some Basic Concipts Cleavage: a secondary fabric element formed under low temperature conditions which depends on rock tendency to split along planes. 7 Ahmed Essam Ayad
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. 8 Ahmed Essam Ayad
Primary Structure : Foliation Prefered orientation of Bubbles: characterizes some types of igneous extrusive rocks especially " Pumice fragments ". 9 Ahmed Essam Ayad
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. 10 Ahmed Essam Ayad
Primary Structure : Foliation M a g m a t i c l a y e r i n g : characterizes cumulate magmatic rocks. 11 Ahmed Essam Ayad
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. 12 Ahmed Essam Ayad
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 Ahmed Essam Ayad
Secondary Structure : Foliation 14 Ahmed Essam Ayad
Spaced Foliation : Disjunctive 15 Ahmed Essam Ayad
Disjunctive : Styolitic 16 Ahmed Essam Ayad
Disjunctive : Anastomosing 17 Ahmed Essam Ayad
Spaced Foliation : Crenulation 18 Ahmed Essam Ayad
Morphological Classification 19 Ahmed Essam Ayad
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. 20 Ahmed Essam Ayad
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. 21 Ahmed Essam Ayad
Pencil Vs. Slaty Cleavage 22 Ahmed Essam Ayad
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. 23 Ahmed Essam Ayad
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. 24 Ahmed Essam Ayad
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. 25 Ahmed Essam Ayad
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. 26 Ahmed Essam Ayad
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. 27 Ahmed Essam Ayad
Mylonite Classification 28 Ahmed Essam Ayad
Thanks E-mail: geo.ahmedessam@gmail.com 29

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Structural geology : foliation

  • 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. 2 Ahmed Essam Ayad
  • 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. 3 Ahmed Essam Ayad
  • 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. 4 Ahmed Essam Ayad
  • 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. 5 Ahmed Essam Ayad
  • 7. Some Basic Concipts Cleavage: a secondary fabric element formed under low temperature conditions which depends on rock tendency to split along planes. 7 Ahmed Essam Ayad
  • 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. 8 Ahmed Essam Ayad
  • 9. Primary Structure : Foliation Prefered orientation of Bubbles: characterizes some types of igneous extrusive rocks especially " Pumice fragments ". 9 Ahmed Essam Ayad
  • 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. 10 Ahmed Essam Ayad
  • 11. Primary Structure : Foliation M a g m a t i c l a y e r i n g : characterizes cumulate magmatic rocks. 11 Ahmed Essam Ayad
  • 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. 12 Ahmed Essam Ayad
  • 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 Ahmed Essam Ayad
  • 14. Secondary Structure : Foliation 14 Ahmed Essam Ayad
  • 15. Spaced Foliation : Disjunctive 15 Ahmed Essam Ayad
  • 18. Spaced Foliation : Crenulation 18 Ahmed Essam Ayad
  • 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. 20 Ahmed Essam Ayad
  • 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. 21 Ahmed Essam Ayad
  • 22. Pencil Vs. Slaty Cleavage 22 Ahmed Essam Ayad
  • 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. 23 Ahmed Essam Ayad
  • 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. 24 Ahmed Essam Ayad
  • 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. 25 Ahmed Essam Ayad
  • 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. 26 Ahmed Essam Ayad
  • 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. 27 Ahmed Essam Ayad