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Mountain building1


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  • 2. Cotopaxi Volcano in Ecuador
  • 3. Cotopaxi
  • 4.
    • Deformation – refers of all changes in the original shape or size of a rock body.
    • Brittle deformation – at the earth’s surface, low temperatures and low pressures, solid rock fractures
    • Ductile deformation – deep with in the Earth, high temperatures and high pressures, rock is deformed without breaking
    • The mineral composition and texture also affects how it will deform.
    • Small stresses applied over time will cause the rock to bend.
  • 5.
    • Stress – force per unit area acting on a solid
    • Strain – the change in shape or volume
    • Tensional stress – causes a material to be stretched
    • Compressional stress – causes a material to shorten
    • Shear stress – causes a material to be distorted
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    • Folds – during mountain building flat-lying sedimentary and igneous rock are bent into a series of ripples
    • Anticlines – arching of rock layers
    • Synclines – downfolds or troughs
    • Monoclines – large step-like folds
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    • Faults – fractures in the crust along which movement has taken place
    • Normal fault – when the hanging wall block moves down relative to the footwall block, caused by tensional forces
    • Reverse fault – the hanging wall block moves up relative to the footwall, caused by compressional forces
    • Thrust faults – reverse faults with dips less than 45o
    • Strike-slip faults – the movement is horizontal and parallel, caused by shear stress, San Andreas fault
    • Joints – most common rock structure, fractures along which no appreciable movement has occurred
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    • Mountains – classified by the dominant processes that deformed them
    • Folded Mountains – formed by folding, compressional stress is the major force that formed them; examples – Appalachians, Alps, northern Rocky Mountains
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    • Fault-block Mountains – mountains that form as large blocks of crust are uplifted and tilted along normal faults; examples – Tetons Range, Sierra Nevadas
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    • Horst and Grabens – formed from tensional forces, horsts are uplifted structures and grabens is where the blocks dropped down; example – the Basin and Range region of Nevada, California and Utah
  • 21.
    • Domes – formed by upwarping and exposing older igneous and metamorphic rock; example – Back Hills of South Dakota
    • Basins – downwarping structures having a circular shape
  • 22. Mountain Building – Orogenesis
    • Mountain Building at Convergent Boundaries – colliding plates provide the compressional forces that deform rock
    • Oceanic-Oceanic Convergence – forms volcanic island arcs, Aleutian Islands of Alaska
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    • Ocean- Continental Convergence – ocean crust subducts the continental crust, the continental crust is deformed, creates volcanic arcs on continent
    • Accretionary wedge – accumulation of different sedimentary and metamorphic rocks
    • Continent-Continent Convergence – form folded mountains; examples – Himalayas, Ural mountains
  • 25.
    • Mountain Building at Divergent Boundaries – fault-block mountains
    • Non-Boundary Mountains – Hawaiian Islands are volcanic islands formed by a hot spot
    • Continental Accretion – smaller crustal fragments collide and merge with continental margins; example – many of mountains rimming the Pacific Canada and Alaska
    • Terranes – any crustal fragment that has a geologic history distinct from adjoining terranes
  • 26.
    • Isostacy – a floating crust in gravitational balance. As mountains erode, the crust rises in response to the reduced load. Erosion and uplift continue until the mountains reach normal crustal thickness
    • The weight of the ice sheet during the Pleistocene depressed the Earth’s crust hundreds of meters. Since the ice age, uplift has occurred
  • 27.