29 Continental Evolution II (1)
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Transcript of 29 Continental Evolution II (1)
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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