Mountains, mountain building, & growth of continents.

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mountains, mountain building, & growth of continents



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


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)





mountains and mountain buildingancient mountain beltseroded flat: form stable, interior of continents: craton

-- oldest parts are shields -- e.g. Canadian shield




• thick sequences of folded and faulted rocks --typically marine (formed in ocean) sedimentary rocks

• metamorphic rocks locally common


• 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



green arrow shows Lewis Thrust, Glacier National Park


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



Mt. Everest



Himalayan foothills



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


after convergence stops, erosion and uplift occur

--isostatic adjustment--to thin continental root


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



topography







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)

Mountains, mountain building, & growth of continents.

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