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mountains, mountain building, & growth of continents. mountains and mountain building. mountain belts. • are chains of mountains 1,000’s of km’s long. • sit at or near edges of continents. • form from tectonic or volcanic processes over millions of years-- geosphere.

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Presentation Transcript
slide2

mountains and mountain building

mountain belts

• are chains of mountains 1,000’s of km’s long

• sit at or near edges of continents

• form from tectonic or volcanic processes

over millions of years--geosphere

• erode as they grow higher and steeper--hydrosphere

• cause precipitation as air rises above them--atmosphere

slide3

mountains and mountain building

mountain belts

are very long

compared to

their width

North American

Cordillera

extends from

Alaska

to

Panama

slide4

mountains and mountain building

mountain 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)

slide5

mountains and mountain building

ancient mountain belts

eroded flat:

form stable, interior of continents: craton

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

slide6

mountains and mountain building

mountain belts

• thick sequences of folded and faulted rocks

--typically marine (formed in ocean) sedimentary rocks

• metamorphic rocks locally common

slide7

mountains and mountain building

mountain belts

• fold and thrust belts

--crust shortened and thickened

(remember: thrust faults indicate shortening)

• common at convergent boundaries (compression)

slide8

mountains and mountain building

mountain belts

fold-thrust mountains

Himalayas, Alps, Urals, northern and Canadian Rockies

green arrow shows Lewis Thrust, Glacier National Park

slide9

mountains and mountain building

evolution of mountain belts

accumulation stage

rocks (sedimentary) that will

later be uplifted, faulted, and

folded into mountains are

deposited in opening ocean

(sea floor spreading)

orogenic stage

mountain building episode

from plate convergence

(provides compression necessary for thrusting)

slide10

Mt. Everest

Himalayan foothills

Swiss Alps

slide11

mountains and mountain building

evolution 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

slide12

mountains and mountain building

evolution of mountain belts

after convergence stops, erosion and uplift occur

--isostatic adjustment--

to thin continental root

slide13

mountains and mountain building

evolution 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)

slide14

topography

mountains and mountain building

evolution of mountain belts

fault-block mountains

Basin and Range, western US

slide16

mountains and mountain building

evolution of Basin and Range

crustal extension dominates today

--accompanied by high heat flow--

older period of thrusting and

formation of mountains when

continental root developed

uplift and erosion yield extension

but must explain high heat flow

delamination of mantle?

mantle lithosphere detaches

and sinks into asthenosphere

warm asthenosphere

fills space and results in

stretching of crust

slide17

mountains and mountain building

modern Basin and Range

extension at surface; upwelling asthenosphere at depth

slide18

mountains and mountain building

continents grow as

mountain belts evolve at

active continental margins

igneous activity adds

new crust

sedimentary rocks

originally deposited

in ocean

are uplifted, folded,

and faulted to

form new terranes

that are “accreted”

or added to

continent along its edge

accreted terranes in

western US

slide19

continental growth

continents decrease in age toward their margins

slide20

growth of continents: US example

geologic map of the United States

on-going subduction

(Cascadia)

Basin and Range

(rifting)

Canadian shield

transform

boundary

(San Andreas)

Paleozoic

orogenic belts

(Appalachians)

craton

Paleozoic

to Recent

active

margin

Mesozoic to

Recent

passive margin

Paleozoic to Recent

orogenic belts

Paleozoic

orogenic belts

(Ouachitas, Marathons)

from: http://pubs.usgs.gov/publications/text