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Lecture Outlines
Physical Geology, 14/e
Plummer, Carlson & Hammersley
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Mountain Belts and the
Continental Crust
Physical Geology 14/e, Chapter 20
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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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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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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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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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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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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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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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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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End of Chapter 20