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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
