8' Plate Tectonics on Planetary Bodies William Wilcock

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8. Plate Tectonics on Planetary BodiesWilliam
Wilcock
OCEAN/ESS 410
Fall 2006
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Terrestrial Planets
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Age of Terrestrial Planet Surfaces
Relative amount of surface area
2/3 of Earths surface formed
within the last 200 million years
Planets
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3
2
1
form
Age of Surface (billions of years)
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Earth

• Plate tectonics replace 2/3 of the surface every
  100 Myr and modify the remaining 1/3 on
  geologically short timescales.
• Evidence at a scale we might see on other planets
• Linear and rifts and arcuate compression zones
• Transform faults and fracture zones (adjacent
  transform faults are parallel after adjusting for
  geometry of the earth).
• Continuous plate boundaries
• Volcanic Island chains - plates moving over fixed
  mantle plume (melt source)
• Topography variations consistent with aging
  plates.

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Mars
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Mars

• Last eruption on Olympus Mons 2 to 100 Myr ago
• Surface appears to be one plate
• Evidence for plate tectonics in the past is
  controversial
• Smaller radius means it cooled down quicker than
  earth and the lithosphere (the rigid cold layer)
  is thicker - too strong for plate tectonics
• Large volcanoes show surface has not moved
  relative to mantle plumes

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Mantle Convection in Mars
model by Walter Kiefer
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Venus
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VENUS

• Burst of volcanism 600-700 MYrs ago
• Either steady state plate tectonics stopped
  then or Venus undergoes episodic bursts of
  volcanism
• Venus has lost its water.
• Water in the mantle may be critical for plate
  tectonics because it weakens the mantle and
  lubricates the motion of the plates.
• In the absence of lubrication the heat from
  radioactivity may build up inside Venus until it
  is released in catastrophic mantle overturning
  events.

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• In class we will define the terms lithosphere and
  asthenosphere and explain why water in the
  mantle weakens the asthenosphere and lubricates
  plate tectonics