Class 1' Earth Structure and Plate Tectonics William Wilcock

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Class 1. Earth Structure and Plate Tectonics
William Wilcock
OCEAN/ESS 410
Fall, 2007
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Plate Tectonics
fracture zone
island arc
trench
MOR
trench
earthquakes
continental crust
earthquakes
ocean crust
magma
melt
Mantle
melt
Mantle
sediments,cold crust mantle
adiabatically rising mantle material
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InternalStructure of the Earth.The Earth is a
differentiated Planet
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Planetary Differentiation - early in Earths
history
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The Earth as a Heat Engine

• Heat generated by
• Radioactivity (U, Th, K isotopes)
• Solidification of Inner Core
• Heat Lost from the Earth by
• Mantle Convection

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Heat Convection - Heating From Below
Conduction Important

Convection (or advection) refers to the transport
of heat by motion in a liquid or a gas It is a
very efficient means to transport heat
Thermal Boundary Layer
Upwelling Plume
Downwelling Plume
Convection Important
Thermal Boundary Layer

Conduction Important
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A simplistic model of mantle convection and plate
tectonics
You will commonly see mantle convection depicted
in a simple manner, similar to this figure. This
depiction is reasonable at subduction zones but
not very accurate at mid-ocean ridges.
(figure from Earth by F. Press and R. Siever,
3rd. edition, 1982)
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Heat Convection - Internal Heating
Thermal Boundary Layer
Convection in the Earths mantle is driven
primarily (80-90) by internal heating from the
decay of long lived radioactive isotopes of
potassium, uranium and thorium and not heat loss
from the core (10-20). The pattern of convection
for internal heating is different from bottom
heating.
Broad Region of Diffuse Upwelling
Downwelling Plume
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Many Aspects Mantle Convection in the Earth are
Still Incompletely Understood
volcanic island chain
ocean crust
mid-ocean ridge
trench
island arc
cont. crust
After Kellogg et al., 1999
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Global Bathymetry
Sandwell and Smith
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Plate Tectonic Theory

• The Earths surface is made up of a number of a
  small number of rigid plates that move relative
  to one another. Deformation near the earths
  surface is concentrated along the boundaries
  between. Plates boundaries may be sites of
• Divergence - oceanic spreading centers and rifts
• Convergence - subduction zones and regions of
  continental collision
• Motions that are orthogonal to the plate boundary
  - transform faults.

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Tectonic Plates