1. Lecture Outlines Physical Geology, 14/e
Plummer, Carlson & Hammersley
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2. Mountain Belts and the Continental Crust Physical Geology 14/e, Chapter 20
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3. Mountain Belts & Earth’s Systems
Mountain belts – chains of mountain ranges that are 1000s of km long
commonly located at or near the edges of continental landmasses
part of the geosphere
as they grow higher and steeper, erosion rates increase
air rising over mountain ranges results in precipitation and erosion
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4. Characteristics of Mountain Belts
Mountain belts – very long compared to their width
older mountain ranges tend to be lower in height than younger ones due to erosion
ancient mountain belts have eroded nearly flat to form the stable cores (cratons) of the continents
shields - areas of cratons laid bare by erosion
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5. Rock Patterns in Mountain Belts
Mountain belts – typically contain thick sequences of folded and faulted sedimentary rocks, often of marine origin
Fold and thrust belts – indicate crustal shortening produced by compression
common at convergent boundaries
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6. Rock Patterns in Mountain Belts
Erosion-resistant batholiths – may be left behind as mountain ranges after long periods of erosion
localized tension in uplifting mountain belts can result in normal faulting
earthquakes common along faults in mountain ranges
horsts and grabens can produce mountains and valleys
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7. Evolution of Mountain Belts
Accumulation stage – rocks that will later be uplifted into mountains are deposited
typically occurs in marine environment, at opening ocean basin or convergent plate boundary
Orogenic stage – mountains are uplifted at convergent boundaries
result of ocean-continent, arc-continent, or continent-continent convergence
subsequent gravitational collapse and spreading may bring deep-seated rocks to the surface
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8. Evolution of Mountain Belts
Block-faulting – a long period of erosion, uplift occurs after convergence stops
as erosion removes overlying rock, the crustal root of a mountain range rises by isostatic adjustment
tension in uplifting and spreading crust results in normal faulting and fault-block mountain ranges
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9. Evolution of Mountain Belts
Basin-and-Range province – may be the result of delamination
overthickened mantle lithosphere beneath old mountain belt may detach and sink into asthenosphere
resulting inflow of hot asthenosphere can stretch and thin overlying crust, producing normal faults
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10. Growth of Continents
Continents grow larger as mountain belts evolve along their margins
accumulation and igneous activity add new continental crust
New accreted terranes can be added with each episode of convergence
Western North America (especially Alaska) contains many such terranes
numerous terranes, of gradually decreasing age, surround older cratons that form the cores of the continents
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11. End of Chapter 20