<P> Antigorite = Forsterite + Enstatite + H O </P> <P> Transition into the eclogite facies is proposed to be the source of earthquakes at depths greater than 70 km . These earthquakes are caused by the contraction of the slab as minerals transition into more compact crystal structures . The depth of these earthquakes on the subducting slab is known as the Wadati--Benioff zone . </P> <P> Paired metamorphic belts are a set of parallel metamorphic rock units parallel to a subduction zone displaying two contrasting metamorphic conditions and thus two distinctive mineral assemblages . Nearest the trench is a zone of low temperature, high pressure metamorphic conditions characterized by blueschist to eclogite facies assemblages . This assemblage is associated with subduction along the trench and low heat flow . Nearest the arc is a zone of high temperature - low pressure metamorphic conditions characterized by amphibolite to granulite facies mineral assemblages such as aluminosilicates, cordierite, and orthopyroxenes . This assemblage is associated with high heat flow generated by melting beneath the volcanic arc . </P>

What does metamorphic rock turn into at subduction zones
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