Mountain building1


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Mountain building1

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