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Evolution of the Continents IILecture by

Professor John Platt

Reading assignments for these twoReading assignments for these twolectures: Tarbuck & Lutgens, ch 22, p.lectures: Tarbuck & Lutgens, ch 22, p.618-624, and ch 14.618-624, and ch 14.

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Topics covered in this lecture

The modern world (Phanerozoic Eon)

Mechanisms of continental growth

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The Phanerozoic

540 Ma to present

Plate tectonic processes comparable to present Continued continental growth

Formation and break-up of Pangea

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United Plates

of

America Late Proterozoic

and Phanerozoic

mountain chains

have added new

material around theold shield

Many of these

chains represent an

old continental

collision

The youngest

addition is the

Cordillera

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Pangea

During the

Phanerozoic, the

supercontinent ofPangea was

created ~ 280

Ma, and broke up

by ~200 Ma.

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Mechanisms of Continental Growth

and Modification

1. Accretion of sediment along subduction zones

2. Emplacement of ophiolites

3. Magmatism above subduction zones

4. Accretion of island arcs

5. Accretion of continental fragments

6. Lateral translation of continental fragments

7. Continental collision

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1. Accretion of sediment in subduction zones

Makran Ranges of Pakistan. Young sediment has been

accreted to the south Asian margin: accretionary wedge

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Sand deposited in the deep ocean, then accreted to the continental margin

Makran Ranges

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Nankai trough accretionary wedge

Moore et al 1990

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2. Magmatism above subduction zones

Mt Rainier and Seattle

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3. Magmatism at mid-ocean ridges

Oceanic crust forms as a result of partial

melting in the mantle during plate divergence

Magma is basaltic in composition

Forms a crustal layer of intrusive and volcanic

rocks about 6 km thick

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Magmatism at mid-ocean ridges

Magma cools toform 6 km thickoceanic crust

Forms distinctive

sequence ofintrusive andextrusive rocks

locally preservedon land:

Ophiolite

sequence

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4. Accretion of island arcs

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5. Accretion

of continental

fragments

Much of the North

American Cordilleraconsists of accreted

terranes, including

continental

fragments, island

arcs, and

accretionary wedges

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6. Lateral

translation of

continentalfragments

The western marginof North America is

being translated

northwestward along

the San Andreas

Fault

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7. Continental collision

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Continental collision creates thick crust and spectacular

mountain ranges. Shishepangma (Himalayas): 8,013 m

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Continental Collision

Continental collision sweeps up much material from the

oceans and incorporates them into the continents

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United Plates

of

America Late Proterozoic

and Phanerozoic

mountain chains

have added new

material around theold shield

Many of these

chains represent an

old continental

collision

The youngest

addition is the

Cordillera