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Contents of 12.4 What is the evidence that subduction occurs at convergent plate boundaries?

• The Wadati-Benioff zone of earthquake foci outlines subducting plates descending at an angle from deep-sea trenches into the asthenosphere.
• Seismic tomography shows this zone as having unusually fast seismic velocity in the asthenosphere. Subduction zones also show low heat flow. These data reveal the cold, dense plates sinking into the asthenosphere.
• Metamorphic fluids released from the subducting plate cause melting in the surrounding asthenosphere. Magma is generated, intrudes into the overlying lithosphere, and accounts for volcanic activity, high heat flow, and high-temperature metamorphism.

12.4 What is the evidence that subduction occurs at convergent plate boundaries?