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Our transcription: Igneous activity is directly related to plate tectonics. Ocean ridges, zones of spreading in the Earth's oceans is due to the upwelling of molten magma derived from partial melting in the mantle. In melting mantle, the result is a magma that will crystallize to form basalt. That is why basalt is the dominant rock type of ocean ridges, of ocean islands, and of ocean crust. At subduction zones, that ocean crust, made of basalt again, is subducted, taken back down into the Earth's mantle; and it is heated. It then is partially melted. Magma rising from that partial melt rises to form the great volcanoes above the rim of fire.
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