Transcript Magma Supply Vs Magma Plumbing

OCEAN/ESS 410
Plate Tectonics on Planetary
Bodies
William Wilcock
Terrestrial Planets
Relative amount of surface area
Age of Terrestrial Planet Surfaces
2/3 of Earth’s surface formed
within the last 200 million years
Planets
form
4
3
2
1
Age of Surface (billions of years)
Earth
Plate tectonics replace 2/3 of the surface every ~100
Myr and modifies the remaining 1/3 on geologically
short timescales.
Evidence at a scale we might see on other planets
1. Linear rifts and arcuate compression zones
2. Transform faults and fracture zones (adjacent
transform faults are parallel).
3. Continuous plate boundaries
4. Volcanic Island chains - plates moving over fixed
mantle plume (melt source)
5. Topography variations consistent with aging plates.
Global Bathymetry
Sandwell and Smith
Mars
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
Mantle Convection in Mars
model by Walter Kiefer
Venus
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.
In class we will define the terms lithosphere and
asthenosphere and explain why water in the mantle
weakens the asthenosphere and lubricates plate
tectonics