Department of Biological Sciences and Geology

Partial Melting

Partial melting takes place when the subducting slab of an oceanic plate and any sediment brought down with the slab is melted by increasing temperature. Along with rising temperature due to depth, the slab is frictionally heated, and any water carried down with it acts a flux that reduces the melting point of the rock.

Molten material is, so to speak, sweated off the subducting slab and begins to rise. A look at Bowen's reaction series shows that the last-formed silicates, quartz, K-feldspar, muscovite, etc., would be the first to melt. Because a mafic rock and an admixture of sediment rich in quartz, etc., are being melted, the resulting melt is a little less mafic and an andesitic melt is created.

This melt rises to create intermediate lavas in composite type volcanoes that occur near the subduction zone. One place where this happens is along the west coast of South America, where the Avenue of the Volcanoes running along the length of the Andes Mountains is a result. The Andes are part of the "Ring of Fire" that surrounds the Pacific.

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