Plate tectonics: A historical reviewseismo.berkeley.edu/~rallen/eps122/lectures/L02.pdf · EPS 122:...

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EPS 122: Lecture 2 - Plate tectonics: A historical review

Plate tectonics: A historical review

Reading: Tectonics: Fowler Ch 2 p5-10

For those unfamiliar with plate tectonics: Press & Siever “Understanding Earth” Ch 20


A continental jigsaw

1620: Francis Bacon

Africa and South America

fit together

1655: Antonio Snider

Published a sketch

Mid 1800’s:

First proposed that

continents did fit

together

Toward plate tectonics:

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1912: Alfred Wegener – Continental Drift

1. Similar fossils: N America and Europe S America and Africa

2. Similar rock formations across boundaries

Conclusion: There used to be a supercontinent - Pangaea

Flora and fauna Toward plate tectonics:

Mesosaurus Glossopteris


Skeptics Toward plate tectonics:

Wegener’s ideas were only discussed for a decade and then dropped.

• The coastlines don’t match perfectly

• Were the rock formations really the same?

Alternatives:

1. Land masses sank as the Earth cooled and contracted

2. Land bridges between the continents could explain the fossil record

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Bathymetry The plate tectonic revolution

After World War II …no evidence of land bridges!


Vine and Matthews - 1963

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Magnetic stripes

Atlantic Pacific

Plate tectonics


Seafloor age Plate tectonics

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Euler poles Plate tectonics


Morgan 1968 1968

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Morgan 1968


Morgan 1968

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Morgan 1968


Isacks, Oliver, Sykes 1968

1968

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Isacks, Oliver, Sykes 1968 thanks to the WWSSN


Identifying the plates

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Isacks, Oliver, Sykes 1968

Plate motion directions, from what?

Relative motions


Categories of plate boundaries

Divergent • Established mid-ocean ridge • New rift zone, new ocean

Transform • Along mid-ocean ridges • Across continents

Convergent • Ocean – continent • Ocean – ocean

• Continent – continent

Plate tectonics:

What kinds of beach balls?

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Categories of plate boundaries

Divergent • Established mid-ocean ridge Mid-Atlantic Ridge • New rift zone, new ocean East African Rift

Transform • Along mid-ocean ridges Fracture Zones e.g. south Pacific

• Across continents San Andreas Fault

Convergent • Ocean – continent Off west coast of South America • Ocean – ocean Japan Trench, western Pacific • Continent – continent Himalaya

Plate tectonics:


Mid-Atlantic Ridge Divergent boundaries:

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Ocean transforms Transform plate boundaries:

Mid-ocean ridges are

offset by

ocean transforms:

Fracture Zones

Ocean bathymetry map


Ocean transforms Transform plate boundaries:

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San Andreas Fault Transform plate boundaries:


Different types Convergent plate boundaries:

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Hotspot tracks 1963: Wilson’s

Hawaii

Easter

MacDonald

Galapagos


Morgan 1971

…so hotspot tracks provide absolute plate motion

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Plate velocities Plate tectonics

relative and absolute


Diffuse regions of seismicity …and deformation

plate tectonics is not a perfect model

Plate tectonics: A historical reviewseismo.berkeley.edu/~rallen/eps122/lectures/L02.pdf · EPS 122:...

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