Note_-_Chapter_9 - Crags Cracks and Crumples Crustal Deformation and Mountain Building Mountains Mountains are attractive landscape features They

Note_-_Chapter_9 - Crags Cracks and Crumples Crustal...

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Crags, Cracks, and Crumples: Crustal Deformation and Mountain Building Mountains - Mountains are attractive landscape features - They provide vivid evidence of tectonic activity - They are manifestations of geologic processes - Uplift - Deformation - Metamorphism - Mountains frequently occur in elongate, linear belts - Mountain building is a process called orogenesis Orogenesis - the building of Mountains - Mountains are born and have a finite life span - Young mountains are high, steep, and still growing upward - Middle-aged mountains are lowered by erosion Deformation - Deformation changes the character of the rocks - Undeformed (unstrained): - Horizontal beds, spherical sand grains, no folds or faults - Deformed (strained): - Tilted beds, metamorphic alteration, folding and faulting - Deformation results in one or all of the following: - Displacement - change in location - Rotation - change in orientation - Distortion - change in shape - Deformation is often easy to see - Displacement - change in location by faulting - Rotation - change in orientation - Distortion - change in shape Strain - Strain is the change in shape caused by deformation - There are several types of strain: - Stretching - pulling apart - Shortening - squeezing together - Shear - sliding past Brittle vs. Ductile Deformation - There are two major deformation types: brittle and ductile - The type of deformation depends on: - Temperature - Pressure
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- Deformation rate - Composition - Ductile - rocks deform by flowing and folding - Occurs at higher P and T in the deeper crust - Transition to ductile deformation occurs at about 10-15km depth in the continental crust Stress, strain and fracture - Compression takes place when an object is squeezed - Horizontal compression drives collision - Shortens and thickens material Stress - Tensions occur when the ends of an object are pulled apart - Horizontal tension drives crustal rifting - Stretches and thins material - Shear develops when surfaces slide past one another - Shear stress neither thickens nor thins the crust - Pressure occurs when an object feels the same stress on all sides Geologic structures - Geometric features are created during rock deformation - Planar and linear features are present in deformed rock - The 3-D orientation of a place is described by strike and dip - Strike - horizontal intersection with a tilted - Dip - the angle of the surface down from the horizontal Joints and Veins - Groundwater often flows through joints - Dissolved minerals in groundwater precipitation in joints -
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