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Jan 15, 2016
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mountains, mountain building, & growth of continents
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mountains and mountain buildingmountain belts• are chains of mountains 1,000’s of km’s long
• sit at or near edges of continents
• form from tectonic or volcanic processesover millions of years--geosphere
• erode as they grow higher and steeper--hydrosphere
• cause precipitation as air rises above them--atmosphere
mountains and mountain buildingmountain belts
are very longcompared to
their width
North AmericanCordillera
extends fromAlaska
toPanama
mountains and mountain buildingmountain belts
height is related to age: old mountains (100’s of millions of years) (Appalachians) have lower elevations (due to erosion) than young mountains (a few million years) (Himalayas)
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mountains and mountain buildingancient mountain beltseroded flat: form stable, interior of continents: craton
-- oldest parts are shields -- e.g. Canadian shield
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mountains and mountain buildingmountain belts
• thick sequences of folded and faulted rocks --typically marine (formed in ocean) sedimentary rocks
• metamorphic rocks locally common
mountains and mountain buildingmountain belts
• fold and thrust belts --crust shortened and thickened
(remember: thrust faults indicate shortening)
• common at convergent boundaries (compression)
Himalayas, Alps, Urals, northern and Canadian Rockies
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green arrow shows Lewis Thrust, Glacier National Park
mountains and mountain buildingmountain belts
fold-thrust mountains
evolution of mountain beltsmountains and mountain building
accumulation stagerocks (sedimentary) that will later be uplifted, faulted, and
folded into mountains aredeposited in opening ocean
(sea floor spreading)
mountain building episode from plate convergence(provides compression necessary for thrusting)
orogenic stage
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Mt. Everest
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Himalayan foothills
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Swiss Alps
mountains and mountain buildingevolution of mountain belts
when mountains get very tall (e.g. Himalayas), gravitational collapse and spreading may occur
--normal faulting and extension/thinning of crust--uplift of metamorphic rocks from depth as crust thins and spreads
mountains and mountain buildingevolution of mountain belts
after convergence stops, erosion and uplift occur
--isostatic adjustment--to thin continental root
mountains and mountain buildingevolution of mountain belts
uplifting crust spreads and results in tension (extension)that produces normal faulting and creates
fault-block mountains(horsts and grabens from normal faulting)
evolution of mountain beltsfault-block mountains
mountains and mountain building
Basin and Range, western US
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topography
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Basin and Range
evolution of Basin and Rangemountains and mountain building
crustal extension dominates today--accompanied by high heat flow--
older period of thrusting andformation of mountains when
continental root developed
delamination of mantle?mantle lithosphere detachesand sinks into asthenosphere
warm asthenospherefills space and results in
stretching of crust
but must explain high heat flowuplift and erosion yield extension
modern Basin and Rangemountains and mountain building
extension at surface; upwelling asthenosphere at depth
continents grow as mountain belts evolve at active continental margins
mountains and mountain building
igneous activity addsnew crust
sedimentary rocksoriginally deposited
in oceanare uplifted, folded,
and faulted toform new terranesthat are “accreted”
or added tocontinent along its edge
accreted terranes inwestern US
continents decrease in age toward their margins continental growth
geologic map of the United States
Paleozoic to Recent orogenic belts
Paleozoicorogenic belts(Appalachians)
Canadian shield
Paleozoicorogenic belts
(Ouachitas, Marathons)
Mesozoic to Recent
passive margin
Paleozoicto Recent active margin
from: http://pubs.usgs.gov/publications/text
Basin and Range(rifting)
growth of continents: US example
craton
on-going subduction(Cascadia)
transformboundary
(San Andreas)