What is decompression melting? How does it form magma?
Decompression melting is an adiabatic process, that is, it takes place without any change in temperature of the region. Earth's crust is divided into a number of tectonic plates, which are constantly moving over the layer called mantle. This mantle is hundred's of kilometers thick and is actually solid, but behaves plastically. We constantly have a flow of hot mantle towards the earth's surface, only the temperatures are not high enough for melting to take place. At the regions of divergent plate boundaries, such as mid-ocean ridges, the hot mantle material rises up adiabatically and this causes a decompression or reduction in pressure. This adiabatic decompression results in reduction in melting point of the rocks and we end up with basalt magma.
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