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Plate Boundaries (Convergence (O+O (Subduction of denser plate under less…
Plate Boundaries
Convergence
O+O
Subduction of denser plate under less dense plate --> forms oceanic trench in ocean floor at subduction zone
Causes the mantle material to melt forming magma that rises through the crust to form a chain of undersea volcanoes only on less dense plate --> eventually becomes arc of volcanic islands when the rock accumulates
Friction produced during subduction may result in earthquakes due to built up pressure being released at boundary
Eg. Pacific Plate converge with Philippine Plate (slower moving) --> Pacific subducts under forming Mariana Trench and Mariana Islands
O+C
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Forms oceanic trench on oceanic plate, fold mountains on continental plate
Active volcanoes can also form on C plate as magma from mantle material rises through crust --> may result in earthquakes
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Divergence
O+O
Creates fractures in the plate, magma seeps through the cracks and cools forming new rocks --> sea floor spreading
Magma continues to seep through the cracks and cool, forming a mid-oceanic ridge and the rocks eventually accumulate to form undersea volcanoes
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Eg. Mid-Atlantic Ridge (North-American Plate + Eurasian Plate); Azores Islands (North Atlantic Ocean)
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Transform
Collision between the two plates and they slide past each other --> create immense pressure and friction which is released through earthquake
San Andreas Fault betwen Pacific and NA Plate resultng in San Francisco earthquake in 1906 due to movement of avrg 2.5 m in >1 min