Evolution of

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Evolution of




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Presentations text content in Evolution of

Slide1

Evolution ofContinental Crust

Chapter 10

Slide2

Hypsographic Curve

Slide3

Continental Crust Terms

OrogenyEpeirogenyTerraneAccreted TerraneMantle PlumeHot Spot Volcanism

Wilson Cycle

Basin

Dome

Accretion

Craton

Shield

Slide4

Continental Crust

It’s

thick

(30-60km),

It’s

old

(250 - 4000 my),

It’s

light

(

r

= 2.75 g/cm

3

)

It’s

silicic

(dioritic to granitic in composition).

It has a stable interior called the

craton

.

It

grows

at active margins.

It does not

subduct.

Slide5

Continental Crust

Because continental crust is thick and old, it has experienced and recorded many orogenic events.

It is extremely heterogeneous

Oldest continental rocks are about 4 billion years old.

The oldest oceanic rocks are only 200 million years old.

Slide6

Slide7

Slide8

Cratons and Shields

The

craton

is the stable interior part of the continent.

The craton may be covered by a thin (<2km) veneer of sedimentary rocks.

The

shield

is that portion of the craton that is free of sedimentary cover.

Shields occur in Canada, Southern Africa, Western Australia, and Scandinavia.

Slide9

Slide10

Terranes

A

terrane

is a co-genetic block of crust.

Continents are composed of terranes or blocks of similar age and origin.

The terrane we are on gives a metamorphic age of 1800 my.

The CO-WY border is also a terrane boundary

The Wyoming terrane is Archean.

Slide11

Growth of Continents

Continents grow at

active margins

They grow by addition of accreted or exotic terranes.

A

exotic terrane (= accreted terrane)

is a small block of crust “scraped off” a subducting plate.

Much of SE Alaska and British Columbia is composed of accreted terranes.

Slide12

Slide13

Mountain Belts

An

orogeny

is an episode of mountain building.

An

orogenic belt

is a co-genetic belt of mountain ranges. (e.g. Alps, Himalayas, Rocky Mountains)

Mountain belts tend to have thicker sedimentary cover (2-10 km).

Slide14

Wilson Cycle

The cycle of opening and closing of ocean basins is called the

Wilson Cycle.

Continents can be

rifted

by the formation of new ocean crust.

Continents can fuse or collide as in the Alpine-Himalaya

orogeny

.

Slide15

Slide16

Slide17

Plate tectonic movements and ocean basins

Earth System Figure 10.18 (page 232)Go to next slide to begin

Slide18

Rifting splits the continent...

Slide19

…leading to the creation of new oceanic crust.

Slide20

Passive margin cooling occurs and sediment

accumulates.

Slide21

Convergence begins: an oceanic plate subducts

beneath a continental plate, creating a

volcanic chain.

Slide22

Terrane accretion welds material to the continent.

Slide23

Orogeny thickens the crust and builds

mountains, forming a new supercontinent.

Slide24

The continent erodes, thinning the crust. Rifting

may begin the process again.

Slide25

Plumes and Hot Spots

A ‘

Plume’

is a small convective upwelling from the mantle.

Plumes may cause ‘

hot spot’

volcanism

Yellowstone

Hawaii

Slide26

Plume Hypothesis

Slide27

Slide28

Orogeny and Epeirogeny

O

rogeny

is an episode of mountain building.

Himalayas Alps

Rocky Mtns Appalachians

Epeirogeny

is regional vertical movement of continental crust

Glacial rebound in NE US

Rocky Mountains ??

Slide29

Epeirogeny: example

Glacial Rebound

Slide30

Epeirogeny

1 mm/y = 1000 m/My (!!)

Slide31

Continental Crust

Western US has several terranes

Coast Ranges

Cascades - Sierra Nevada

Columbia Plateau

Snake River (Hot spot track?)

Basin and Range

Colorado Plateau

Rocky Mountains

Great Plains

Slide32

Slide33

Slide34

Continental Crust Terms

OrogenyEpeirogenyTerraneAccreted TerraneMantle PlumeHot Spot VolcanismHypsographic Curve

Wilson Cycle

Basin

Accretion

Craton

Shield

Slide35

Clicker Question:A small block of crust added on to the active margin of a continent is called a(n)

A. Accreted Terrane

B. Shield

C. Craton

D. Mantle Plume

E. Epeirogeny

Slide36

The stable interior portion of a continent is the:

A. Accreted Terrane

B. Shield

C. Craton

D. Mantle Plume

E. Epeirogeny

Slide37

An episode of mountain building is called a(n)

A. Accreted

Terrane

B. Shield

C.

Craton

D.

Orogeny

E.

Epeirogeny

Slide38

Upward or downward movement of a region of continental crust is called a(n)

A. Accreted

Terrane

B. Shield

C.

Craton

D.

Orogeny

E.

Epeirogeny

Slide39

The stable interior portion of a continent that is not covered by sediments is the:

A. Accreted Terrane

B. Shield

C. Craton

D. Mantle Plume

E. Epeirogeny


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