Chapter 17 PM notecards

Chapter 17 PM notecards - Chapter 17 Convergence Collision...

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Chapter 17 Convergent Plate Margins 1) What type of crust is subducted? oceanic Why are there no subduction zones in the middle of continents? The buoyancy of the plates does not allow them to sink under one another 2) Draw a cross section showing the following features: volcanic arc, forearc basin, trench/slope break, accretionary prism, trench, “outer swell” or “peripheral bulge”. Volcanic arc- consists of intermediate to felsic volcanic rocks at the surface with plutonic intrusions beneath. Source is from partial melts in the downgoing slab and upper plate. volatiles in the suducted plate reduce the melting temperature. Forearc basin- bounded by the trench-slope break and the volacnic arc. It accumulates sediment mostly from the arc Trench/slope break- a ridge at the top of the accretionary prism, formed as the prism is pushed up by the material accumulating from the downgoing slab. Accretionary prism- where sediment and other crustal material brought along by the descending plate is scrapped off and transferred to the overriding plate. Trench- depression in the ocean floor where the plate turns downward Outer swell- is an upward bulge caused by the flexural rigidity as the plate bends down. may have normal faults due to the bending extension of the outer curve 3) What is “roll-back”? sinking of subducting plate
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Down-going slab 4) What causes the “outer swell”? flexing of the subducting plate Why are there extensional fault there? The outer part of the oceanic crust bulges causing normal faults to relieve the stress 5) What is the Wadati-Benioff zone? Subduction zone How is it defined? It is the thrust fault where the two plates are moving What is its dip angle? The angle the subducted plate is dipping is controlled by the sinking rate of the plate and velocity 6) How deep are earthquakes found in the down-going slab? 700km Why do some show slab parallel compression and others extension? The slab speeds up as it is pulled down causing extension and slow downs as it reaches the end of how far it can travel causing compression
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Chapter 17 PM notecards - Chapter 17 Convergence Collision...

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