Changes

|competition=December 2014

|competition=December 2014

}}

}}

'''Structural geology''' is the study of the three – dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present – day rock geometrics to uncover information about the history of deformation (strain) in the rocks, and ultimately, to understand the stress field that resulted in the observed strain and geometrics. This understanding of the dynamics of the stress field can be linked to important events in the regional geologic  past; a common goal is to understand  the structural related evolution  of a particular area with respect to regionally widespread patterns of rock deformation (mountain building, rifting )due to plate tectonics  

'''Structural geology''' is the study of the three-dimensional distribution of rock units with respect to their [[deformation]]al histories. The primary goal of structural geology is to use measurements of present-day rock geometrics to uncover information about the history of deformation (strain) in the rocks, and ultimately, to understand the stress field that resulted in the observed strain and geometrics. This understanding of the dynamics of the stress field can be linked to important events in the regional geologic  past; a common goal is to understand  the structural related evolution  of a particular area with respect to regionally widespread patterns of rock deformation (mountain building, rifting )due to plate tectonics  

==Growth fault==

==Growth fault==

[[File:Fig 1 Emad final thin boundary2.jpg|thumb|300px|{{figure number|2}} Sketch showing evolution stages of three growth faults. The black arrow shows the direction of evolution.]]

[[File:Fig 1 Emad final thin boundary2.jpg|thumb|300px|{{figure number|2}} Sketch showing evolution stages of three growth faults. The black arrow shows the direction of evolution.]]

Growth faults are syn-depositional or syn-sedimentary extensional faults that initiate and evolve at the margins of continental plates. They extend parallel to passive margins that have high sediment supply. Their fault plane dips mostly toward the basin and has long-term continuous displacement. [[:File:Fig_1_Emad_final_thin_boundary1.jpg|Figure 1]] shows a growth fault with a concave upward fault plane that has high updip angle and flattened at its base into zone of detachment. This angle is continuously changing from nearly vertical in the up dip area to nearly horizontal in the down dip area.

[[Growth fault]]s are syndepositional or synsedimentary extensional faults that initiate and evolve at the margins of continental plates. They extend parallel to passive margins that have high sediment supply. Their fault plane [[dip]]s mostly toward the basin and has long-term continuous displacement. [[:File:Fig_1_Emad_final_thin_boundary1.jpg|Figure 1]] shows a growth fault with a concave upward fault plane that has high updip angle and flattened at its base into zone of detachment. This angle is continuously changing from nearly vertical in the up dip area to nearly horizontal in the down dip area.

Growth faults maturation is a long term process that takes millions of years with slip rate ranges between 0.2-1.2 millimeters per year. It starts when sedimentary sequences are deposited on top of each other above a thick evaporite layer ([[:File:Fig 1 Emad final thin boundary2.jpg|Figure 2]]). A growth fault is initiated when the evaporite layer can no longer support the overlying sequences. The thicker and denser portion applies much more pressure on the evaporite layer than the thin portion. As a result, a flow within the evaporite layer is initiated from high pressure areas toward low pressure areas causing growth ridges to form below the thin portion. Also, sinking zones are noticed among these ridges at areas where thicker and denser layers form ([[:File:Fig 1 Emad final thin boundary2.jpg|Figure 2]]).

Growth faults [[maturation]] is a long term process that takes millions of years with slip rate ranges between 0.2-1.2 millimeters per year. It starts when sedimentary sequences are deposited on top of each other above a thick [[evaporite]] layer ([[:File:Fig 1 Emad final thin boundary2.jpg|Figure 2]]). A growth fault is initiated when the evaporite layer can no longer support the overlying sequences. The thicker and denser portion applies much more pressure on the evaporite layer than the thin portion. As a result, a flow within the evaporite layer is initiated from high pressure areas toward low pressure areas causing growth ridges to form below the thin portion. Also, sinking zones are noticed among these ridges at areas where thicker and denser layers form ([[:File:Fig 1 Emad final thin boundary2.jpg|Figure 2]]).

===Accompanied structures===

===Accompanied structures===

===Driving force===

===Driving force===

The main driving forces of the growth faults are the deferential sediments load and the low density layers - evaporites or over-pressured shale - that are formed during or right after the rifting process. Growth faults are located mainly within passive margin sedimentary wedges where tectonic forces have minimum or no effect. These passive margins receive millions of tons of sediments every year which are concentrated on the continental shelf below base level and above areas where the water velocity is no longer supporting the particles weight. This zone is called depositional center (depocenter for short) and has higher sediments load.Earthquakes arise and result ease of the force along the growth fault plane.

The main driving forces of the growth faults are the deferential sediments load and the low density layers - evaporites or over-pressured shale - that are formed during or right after the rifting process. Growth faults are located mainly within passive margin sedimentary wedges where tectonic forces have minimum or no effect. These passive margins receive millions of tons of sediments every year which are concentrated on the continental shelf below base level and above areas where the water velocity is no longer supporting the particles weight. This zone is called depositional center ([[depocenter]] for short) and has higher sediments load.Earthquakes arise and result ease of the force along the growth fault plane.

===Importance of growth faults===

===Importance of growth faults===

Growth faults have great significance for stratigraphy, structural geology and the petroleum industry. They account for relative and eustatic sea level changes and accommodation space left for new sediments. Likewise, growth faults are connected directly to the subsidence in the coastal and continental shelf areas. Moreover, they explain lateral thickness variation of sedimentary sequences across these faults. The updip area on the downthrown block is the main target of oil and gas exploration because it has synthetic and antithetic faults and rollover anticlines. These are considered as structural traps preventing oil and gas from escaping

Growth faults have great significance for stratigraphy, structural geology and the petroleum industry. They account for relative and eustatic sea level changes and accommodation space left for new sediments. Likewise, growth faults are connected directly to the subsidence in the coastal and continental shelf areas. Moreover, they explain [[lateral]] thickness variation of sedimentary sequences across these faults. The updip area on the downthrown block is the main target of oil and gas exploration because it has synthetic and antithetic faults and rollover anticlines. These are considered as structural traps preventing oil and gas from escaping

==Deformation of rocks==

==Deformation of rocks==

<gallery mode=packed heights=300px>

<gallery mode=packed heights=250px>

File:Structural_Geology_Fig-3.0.png|{{figure number|3.0}}

File:Structural_Geology_Fig-3.0.png|{{figure number|3}}

File:Structural_Geology_Fig-3.1.png|{{figure number|3.1}} Small Scale Folds

File:Structural_Geology_Fig-3.1.png|{{figure number|4}} Small Scale Folds

File:Structural_Geology_Fig-3.2.png|{{figure number|3.2}} Small Scale Faults

File:Structural_Geology_Fig-3.2.png|{{figure number|5}} Small Scale Faults

</gallery>

</gallery>

   

   

'''Rock Deformation'''

'''Rock Deformation'''

* Large scale deformation of the Earth’s crust = Plate Tectonics

* Large scale deformation of the Earth’s [[crust]] = [[plate tectonics]]

* Smaller scale deformation = structural geology

* Smaller scale deformation = structural geology

'''Deformation of rocks'''

'''Deformation of rocks'''

* Folds and faults are geologic structures

* [[Fold]]s and faults are geologic structures

'''Deformation – Stress vs. Strain'''

'''Deformation – Stress vs. Strain'''

'''Stress'''

'''Stress'''

* The ''force'' that acts on a rock unit to change its shape and/or its volume Causes strain or deformation

* The ''force'' that acts on a rock unit to change its shape and/or its volume Causes strain or [[deformation]].

Types of directed Stress include

Types of directed Stress include

* Compression

* [[Compression]]

* Tension

* [[Tension]]

* Shear

* [[Shear]]

; Compression: Action of coincident oppositely directed forces acting towards each other

; Compression: Action of coincident oppositely directed forces acting towards each other

</gallery>

</gallery>

[[File:Structural_Geology_Fig-3.6.png|300px|thumb|{{figure number|3.3}}Differential stress]]

[[File:Structural_Geology_Fig-3.6.png|300px|thumb|{{figure number|7}}Differential stress]]

'''Strength'''

'''Strength'''

* Temporary change in shape or size that is recovered when the deforming force is removed

* Temporary change in shape or size that is recovered when the deforming force is removed

[[File:Structural_Geology_Fig-3.7.png|center|300px|{{figure number|3.4}}]]

[[File:Structural_Geology_Fig-3.7.png|center|300px|{{figure number|8}}]]

'''Ductile (Plastic) Deformation'''

'''Ductile (Plastic) Deformation'''

<gallery mode=packed>  

<gallery mode=packed>  

File:Structural_Geology_Fig-3.8.png|{{figure number|3.5}} Diagram showing ductile deformation (folding).

File:Structural_Geology_Fig-3.8.png|{{figure number|9}} Diagram showing ductile deformation (folding).

File:Structural_Geology_Fig-3.9.png|{{figure number|3.6}}

File:Structural_Geology_Fig-3.9.png|{{figure number|10}}

</gallery>

</gallery>

* Usually occurs along sub-planar surfaces that separate zones of coherent material

* Usually occurs along sub-planar surfaces that separate zones of coherent material

[[File:Structural_Geology_Fig-3.10.png|center|300px|{{figure number|3.7}}]]

[[File:Structural_Geology_Fig-3.10.png|center|300px|{{figure number|11}}]]

'''Factors that affect deformation'''

'''Factors that affect deformation'''

'''''The variation of these factors determines if a rock will fault or fold.''''

'''''The variation of these factors determines if a rock will fault or fold.''''

[[File:Structural_Geology_Fig-4.0.png|center|300px|{{figure number|3.8}}]]

[[File:Structural_Geology_Fig-4.0.png|center|300px|{{figure number|12}}]]

Brittle Failure  

Brittle Failure  

* (scale - from mm to tens of km)

* (scale - from mm to tens of km)

   

   

[[File:Structural_Geology_Fig-4.1.png|center|300px|{{figure number|3.9}}]]

[[File:Structural_Geology_Fig-4.1.png|center|300px|{{figure number|11}}]]

===Anticlines and Synclines===

===Anticlines and Synclines===

Acticlines and synclines are the up and down folds that usually occur together and are caused by compressional stress.

Acticlines and synclines are the up and down folds that usually occur together and are caused by compressional stress.

   

   

[[File:Structural_Geology_Fig-4.2.png|center|300px|Fig 4.2 Anticline and syncline folds]]

[[File:Structural_Geology_Fig-4.2.png|center|300px|{{figure number|12}}Anticline and syncline folds]]

* Anticlines are folds in which each half of the fold dips away from the crest.   

* Anticlines are folds in which each half of the fold dips away from the crest.   

* Synclines are folds in which each half of the fold dips toward the trough of the fold.  You can remember the difference by noting that anticlines form an “A” shape, and synclines form the bottom of an “S.”  

* Synclines are folds in which each half of the fold dips toward the trough of the fold.  You can remember the difference by noting that anticlines form an “A” shape, and synclines form the bottom of an “S.”  

   

   

[[File:Structural_Geology_Fig-4.3.png|center|300px|Fig 4.3 Folding and surface rock pattern]]

[[File:Structural_Geology_Fig-4.3.png|center|300px|{{figure number|13}}Folding and surface rock pattern]]

After erosion has occurred, geologists can use the patterns of rocks on the surface to determine where anticlines and synclines exist.  In the block diagram above, the top of the block represents the ground surface and what would be shown on a geologic map. The sides of the block show the underground geology. In anticlines, as seen on the ground, the oldest rocks are in the center of the fold.  In synclines, the youngest rocks are in the center of the fold.

After erosion has occurred, geologists can use the patterns of rocks on the surface to determine where anticlines and synclines exist.  In the block diagram above, the top of the block represents the ground surface and what would be shown on a geologic map. The sides of the block show the underground geology. In anticlines, as seen on the ground, the oldest rocks are in the center of the fold.  In synclines, the youngest rocks are in the center of the fold.

   

   

[[File:Structural_Geology_Fig-4.4.png|center|300px|Fig 4.4 Folds in limestone picture.]]

[[File:Structural_Geology_Fig-4.4.png|center|300px|{{figure number|14}}Folds in limestone picture.]]

This intensely folded limestone from Highland County shows how anticlines and synclines typically occur together.  These sharp folds are called "chevron" folds.

This intensely folded limestone from Highland County shows how anticlines and synclines typically occur together.  These sharp folds are called "chevron" folds.

Equipment needed:  

Equipment needed:  

* A compass for measuring direction of dip and strike.   

* A compass for measuring direction of [[dip]] and strike.   

* A clinometer for reading angle of dip.

* A clinometer for reading angle of dip.

** These two are usually combined in a compass clinometer.

** These two are usually combined in a compass clinometer.

==Fracture==

==Fracture==

Fractures are surfaces along which rocks or minerals have broken, thus generating two free surfaces where none existed before.  

[[Fracture]]s are surfaces along which rocks or minerals have broken, thus generating two free surfaces where none existed before.  

Fractures are among the most common of all geologic features. Their study is important because fractures provide information on what kind of stress caused them (history of deformation) and also because they alter the characteristics of the rocks in which they occur: for instance a fracture would weaken a rock (and we need to know that if we build a dam, or a tunnel), and would allow fluids to move through it (and we need to know that if we are looking for oil or gas, or if we are dealing with groundwater.

Fractures are among the most common of all geologic features. Their study is important because fractures provide information on what kind of stress caused them (history of [[deformation]]) and also because they alter the characteristics of the rocks in which they occur: for instance a fracture would weaken a rock (and we need to know that if we build a dam, or a tunnel), and would allow fluids to move through it (and we need to know that if we are looking for oil or gas, or if we are dealing with groundwater.

Fractures and joint are similar

Fractures and joint are similar

==Sources==

==Sources==

# Cazes, C. A.; 2004. "Overlap Zones, Growth Faults, and Sedimentation: Using High Resolution Gravity Data, Livingston Parish, LA.". Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science in The Department of Geology and Geophysics; Louisiana State University, Thesis". p. 147.

# Cazes, C. A., 2004, Overlap zones, growth faults, and sedimentation: Using high resolution gravity data, Livingston Parish, LA: Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science in The Department of Geology and Geophysics; Thesis, Louisiana State University, p. 147.

# Schlische, R.W.; Anders, M.H. (1996). "Stratigraphic effects and tectonic implications of the growth of normal faults and extensional basins. In: Berata, K. (Ed.), Reconstructing the History of the Basin and Range Extension using Sedimentology and Stratigraphy". Geological Society of America303: 183–203. doi:10.1130/0-8137-2303-5.183.

# Schlische, R. W., M. H. Anders, 1996, Stratigraphic effects and tectonic implications of the growth of normal faults and extensional basins, "in" K. Berata, ed., Reconstructing the History of the Basin and Range Extension using Sedimentology and Stratigraphy: Geological Society of America Memoir 303, pp. 183–203.

# Doglioni C.; D’Agostino, N., Mariotti, G., (1998). "Normal faulting versus regional

# Doglioni, C., N. D’Agostino, and G. Mariotti, 1998, Normal faulting versus regional

# Homepage.smc.edu/grippo-alessandro/strct3.html

# http://Homepage.smc.edu/grippo-alessandro/strct3.html

# Wikipedia, the free encyclopedia (www.en.wikipedia.org)

# [http://www.en.wikipedia.org Wikipedia, the free encyclopedia]

# Structural geology ( www.geology.com)

# [http://www.geology.com Structural geology]

# www.princeton/~~achaey/time/course/wiki100k/docs/structures.

# [http://www.princeton/~~achaey/time/course/wiki100k/docs/structures]