More Plate Tectonics

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• More Plate Tectonics

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• A CLOSER LOOK AT PLATE TECTONICS

• Some revision
• Driving forces
• What is the evidence? A bit of history
• Continental drift
•  Ocean exploration the Cold War
• The plate tectonic revolution

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PLATE TECTONICS THE RULES

• Earths surface layer (the lithosphere) is
  divided into a series of rigid plates
• Deformation only occurs at plate boundaries
• If lithosphere is created in one area, it is
  destroyed in another

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Earths lithosphere is divided into plates
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Deformation occurs at plate boundaries
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Three types of plate boundary
From Davidson et al. 1997



divergent convergent
transform
MELTING reduced pressure water
added none
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New plate created old plate destroyed
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Continental Divergence in transition to Oceanic
Divergence
Oceanic Divergence
Continental Divergence
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MILESTONES
1569 Fit of South Atlantic continents
noticed Abraham Ortelius, Belgian cartographer
1910-1924 Continental drift proposed German
climatologist Alfred Wegener Geophysicists
respond that continents cannot plow through
basalt
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The continents fit together!
Rocks of the same strati-graphic ages also fit
together
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Rare fossil provinces, too
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Evidence for continental drift

• Fit of the continents
• Matching of rock types between continents
• Matching of fossils between continents
• BUT, the hypothesis was not accepted at the time

so what changed?
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The Cold War was a great source of funding and
data for geophysicists! Surveys of the oceans
(bathymetry and magnetic field), for submarine
navigation Establishment of the World-Wide
Standardized Seismographic Network (WWSSN) in the
1960s to monitor nuclear tests
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Paleomagnetism
Magnetic minerals in magma
align in an applied magnetic field
This alignment is frozen in as the magma cools
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From the book
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Magnetic intensities
150 km
Zebra pattern of stripes Black normal
magnetization White reverse magnetization
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Wadati-Benioff zones
Evidence for plate subduction
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A summary

• Several lines of evidence supported continental
  drift
• Key evidence for plate tectonics
•  Mid-ocean magnetic anomalies
• Earthquake epicenters and vectors
•  Benioff zones

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• COMBINE THREE BOUNDARY MOTIONS
• WITH TWO TYPES OF CRUST

• DIVERGENT
• ocean ridges  new ocean crust
• continental rifts  thinned continental crust
• TRANSFORM
• oceanic transforms (e.g. Menocino)
• continental transforms (e.g. San Andreas)
• CONVERGENT
• ocean-ocean (e.g. Philippines)  island arc
• ocean-continent (e.g. Andes)  volcanic arc
• continent-continent (e.g. Himalayas)
   thickened
• continental crust