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Candy Bar Tectonics Question of the day: What happens to tectonic plates when they come together? What other ways can they move? http://earthref.org/SCC Scripps Classroom Connection Present day tectonic plates and relative motion http://earthref.org/SCC Scripps Classroom Connection Isostasy http://earthref.org/SCC Scripps Classroom Connection Relative plate motion scenarios: Diagrams Relative motion Divergent Transform Convergent Crust type ContinentalContinental Mountain building Continental Rift ContinetalOceanic Not possible Subduction: Volcanic arc OceanicOceanic Offset features Ocean Spreading Ridge http://earthref.org/SCC Subduction: Island arc Relative motion Divergent Transform Convergent ContinentalContinental Continental rift Offset features Mountain building • Low topography • Cracks in crust open and widen • Thin crust and asthenosphere • Horizontal lengthening • Possible high or low changes in topography due to offset features like rivers or hills • Little change in asthenosphere thickness • Some horizontal lengthening • High topography • Chunks of crust are thrust upward and over crust on the other side • Thick crust and asthenosphere • Horizontal shortening ContinetalOceanic Not possible Offset features Subductionvolcanic arc Crust type OceanicOceanic • Possible high or low changes in topography due to offset features like rivers or hills • Little change in asthenosphere thickness • Some horizontal lengthening Ocean spreading ridge Offset features • Bathymetric high due to warm, less dense lithosphere and upper mantle • Thin crust and asthenosphere • Horizontal lengthening • Possible high or low changes in topography due to offset features like seamounts • Little change in asthenosphere thickness • Some horizontal lengthening • Low topography at trench, high topography at volcanic arc • Thick crust and asthenosphere on continental side • Horizontal shortening Subduction- island arc • Low topography at trench, high topography at island arc • Thick crust and asthenosphere on overriding plate side • Horizontal shortening Relative plate motion scenarios: Photos Relative motion Divergent Transform Convergent Crust type ContinentalContinental Himalaya Mountains, Nepal East African Rift, Ethiopia ContinetalOceanic Not possible San Andreas Fault, Carrizo plain Andes Mountains, South America OceanicOceanic http://earthref.org/SCC Mid Atlantic Ridge Aleutian Islands, Alaska Scripps Classroom Connection Experiment Hypothesis What will happen? 1) Divergent plate boundary ? 2) Transform plate boundary ? 3) Convergent plate boundary ? http://earthref.org/SCC Scripps Classroom Connection Conclusions 1) Relative motion at tectonic plate boundaries: Divergent, Transform, or Convergent 2) Geological features depend on (a) relative motion 3) And (b) continental vs. oceanic crust, through the principle of isostasy http://earthref.org/SCC Scripps Classroom Connection
