Lecture 10 - Chapter 10 Crustal Deformations Structural...

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Chapter 10  Crustal Deformations Structural geology – is a discipline about the deformations of the Earth crust. Structural geologists study the architecture and processes responsible for the crust deformation Deformation is a general term that refers to all changes in the original form and/or size of a rock body Most crustal deformation occurs along plate margins Deformation  involves Force which tends to put stationary objects in motion or changes the motions of moving objects Stress - force applied to a given area Types of stress : Compressional stress – shortens a rock body Tensional stress – tends to elongate or pull apart a rock unit Shear stress – produces a motion similar to slippage that occurs between individual playing cards when the top of the stack is moved relative to the bottom Strain changes in the shape or size of a rock body caused by stress How rocks deform ? Rocks subjected to stresses greater than their own strength begin to deform usually by folding , flowing , OR fracturing General characteristics of rock deformation under confining pressure : Elastic deformation – the rock returns to nearly its original size and shape when the stress is removed Once the elastic limit (strength) of a rock is surpassed, it either fractures  ( brittle  deformation ) or  flows  ( ductile  deformation ) Factors that influence the strength of a rock and how it will deform Temperature . Low t o - rocks exhibit brittle (with fractures) deformation. High t o ductile deform-n . Confining pressure. When the pressure is low (close to the surface) – rocks exhibit brittle deformation, high pressure – ductile deformation Rock type . Igneous rocks with the crystalline structure and strong internal molecular bonds tend to fail by brittle
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Lecture 10 - Chapter 10 Crustal Deformations Structural...

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