23PlanGeol-4 - tectonics Compression Extension Convection...

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Unformatted text preview: tectonics Compression Extension Convection of the mantle creates stresses in the crust Tectonics Deformation of the crust Compression: Stresses push the crust together Mountains, ridges, etc. Extension: Stresses pull the crust apart Valleys, cracks Faults Normal (extension) Faults are where the crust fails, causing deformation Thrust (compression) Present on all planets Earth has special case: Plate Tectonics Strike-slip (shearing) Faults compressional Flooding and Tectonics As planet cools Early - global volcanism Global expansion caused crust to crack lava leaked through Later - global contraction Mantle and core cooled, compressed the crust Compressional tectonics Moon Scarps and Wrinkle Ridges Compression features Faults extensional Moon Venus Graben Extension stress Rift valley Mars Mars Tectonics on Venus Mars - Valles Marinaris - HUGE crack in crust due to stresses of Tharsis volcanoes 15% of Venus is made of highland plateaus and mountain belts Tessera terrain highly deformed and elevated crust Small tectonic features of all types are found everywhere on Venus likely due to the heavy volcanism Bahet and Onatah Coronae Coronae Beheometh volcanic features often many 100s of km in size Believed to be created by upwellings in the mantle Often covered by tectonic fractures and multiple lava flows Faults Normal (extension) Shearing Faults are where the crust fails, causing deformation Thrust (compression) Strike-slip (shearing) Earth - Plate Tectonics Compression Extension Convection of the mantle creates stresses in the crust Plate Tectonics = Extreme Tectonism Seafloor spreading Strong convection drives recycling of crust on time scale of ~100 MY Seafloor crust and continental crust Seafloor crust 5 10 km thick Dense Young Continental crust 20 70 km thick Less dense Varies in age, oldest known is 4.0 billion years old Continents - Blocks of lighter ("granite scum") moved around by convective motions Ocean ridges - volcanism making new oceanic crust (basalt) Plates collide -> mountain chains Plates subduct -> (ocean) trenches Colliding Sinking Spreading Compressing Spreading Rocky Mtns Andes - Pacific ocean plate sinks under south american plate Hot Spots Places where lava is continuously rising through the crust Venus completely re-surfaced by volcanism ~600 MY ago Mercury - lots of craters, little volcanism Earth heavily re-worked surface Mars - some volcanism, south heavily cratered Terrestrial Planets Moon volcanism stopped 3.2 BYago Lots of craters ...
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