How and why does subduction occur? zConvergence yOne plate sinks beneath the other yDense oceanic crust sinks into mantle

What and where is the Wadati-Benioff zone? zInclined array of earthquakes at subduction zone zCorrespond to upper edge of plate

How is magma produced at arcs? zWater from subducting slab lowers the melting point of overlying mantle zNote: water also makes for explosive eruptions…

Where and how do sediments accumulate in arc environments? zSediments accumulate in accretionary wedges at the trench zTwo sources: 1) volcanic arc 2) ocean sediments

Describe deformation of the sediment in the trench z‘Bulldozer action’ scrapes ocean sediments and thrusts material into a wedge

Briefly explain the orogenic cycle using India as an example zGondwana rifts into pieces incuding India zIndia diverges from antarctica but converges on Asia zIndia sutures to Asia

How can continents accumulate additional terrain via plate convergence? z‘collage’ tectonics zExample; The berkshires

Have the continents always looked like they do today? zContinents have grown by lateral accretion yAverage age of continents 2 billion yAverage age of oceans 100 million zAppalachian not at plate boundary

Has the mid-continent always been flat? zContinental shield have the oldest rocks. zComposed of sutured belts of mountains, which were eroded to platforms long ago zThese platforms have harbored shallow seas

What happens to the weak upper layers of crust during collision? zCompression results in thrust faulting and folding into nappes. zDeformation intensifies in the core of the orogen (higher T and P)

What happens to the weak upper layers of crust during collision? zCompression results in thrust faulting and folding into nappes. zDeformation intensifies in the core of the orogen (higher T and P)