Subduction Zone Volcanism

Subduction is when two (2) plates converge and one (1) plate descends under the other. This forms a trench in the ocean floor. As the subducting plate slides under the second plate it carries surface water and hydrated minerals with it. As the depth of the plate increases so do the temperature and the pressure, causing the slab to release water into the mantle wedge. The water lowers the melting temperature of the mantle, causing it to melt. The magma produced varies from basalt to andesite in composition. It rises upward to produce a linear belt of volcanoes parallel to the oceanic trench. If the subduction takes place as an oceanic-oceanic subduction islands are formed, if the subduction takes place as an Oceanic and Continental convergence then a belt of volcanoes will be generated on a continental surface; examples include the Cascade volcanic arc in the Pacific Northwest, and the Andes volcanic arc of South America

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