Module 2B Notes - ESC 1000 Chapter 2 Notes Exploring Earth...

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ESC 1000 Chapter 2 Notes Exploring Earth Science, 1e What-To-Know List 2B - Chapter 8: Mountains, Basins, and Continental Margins 8.1 Why Are Some Regions High in Elevation? Regional elevations are controlled primarily by the thickness of the crust, but they can also be influenced by the temperature and density of materials in the crust and upper mantle. Differences in crustal thickness between regions reflect differences in their geologic histories. Such differences include whether the crust is continental or oceanic, and whether it has been deformed, eroded, or buried. Continents have thick crest (30-50 km) and are higher than ocean basins, which are underlain by oceanic crust which is thinner (7 m) Decreasing Elevation: Normal faulting can thin the crust by displacing higher rocks off lower ones. This decreases crustal thickness and causes a region to subside. Increasing Elevation: Crust that is compressed and shortened by thrust faults also thickens. This thickening causes the region to be uplifted. The thrust can also uplift rocks, forming a mountain. If the crust or mantle beneath a region is heated, the rocks expand and become less dense, resulting in an increase in elevation.
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Describe how heat (and age of the oceanic lithosphere) affect the elevation of the seafloor. Lithosphere varies in thickness from nearly 0 at mid-ocean ridges to more than 150 km beneath some ancient continental interiors. This greatly influences elevation bc the mantle part of the lithosphere is more dense than the asthenosphere. What led to the discovery of Isostasy (regional elevations adjust to the types of thicknesses of rocks at depth)? Higher mountains had thicker crustal roots Lower density crustal material in the roots attracts the suspended weight less than the denser mantle material that the crustal root has displaced. 8.2 Where Do Mountain Belts and High Regions Form? Most regional mountain ranges occur near convergent plate boundaries or where there has been large- scale movement of material in the mantle. West Canada: mountain ranges overlie crust thickened from major thrust faulting, magmatic additions, and collisions w/ island arcs and pieces of continental material. Alps Mountain Range: collisions btwn Europe and smaller continental blocks from the S. Tibetan Plateau/ Himalaya: Indian continent collided (shoved beneath) continental crust of Asia. Andes: (Subduction Zone) Magmatic additions and crustal shortening. East African Rift: magmatic heating of the crust, thinning of lithosphere, and hot spot. Great Divide : No plate boundary here - currently investigating age and cause of uplift.
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Explain how erosion and isostasy help expose deeply formed rocks in eroded mountain belts Summarize differences in regional elevation across North America.
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