Candy Bar Tectonics Question of the day What

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 Continental Mountain building Continental Rift Continetal. Oceanic Not possible Subduction: Volcanic arc Oceanic Offset features Ocean Spreading Ridge http: //earthref. org/SCC Subduction: Island arc

Relative motion Divergent Transform Convergent 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 Continetal. Oceanic Not possible Offset features Subductionvolcanic arc Crust type Oceanic • 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 Continental Himalaya Mountains, Nepal East African Rift, Ethiopia Continetal. Oceanic Not possible San Andreas Fault, Carrizo plain Andes Mountains, South America Oceanic 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