GEOLOGY

Detailed explanation-1: -Areas of lower pressure always have a lower melting point than areas of high pressure. This reduction in overlying pressure, or decompression, enables the mantle rock to melt and form magma. Decompression melting often occurs at divergent boundaries, where tectonic plates separate.

Detailed explanation-2: -At divergent boundaries magma forms because of decompression melting. Decompression melting also takes place within a mantle plume.

Detailed explanation-3: -At divergent plate boundaries hot mantle rock rises into the space where the plates are moving apart. As the hot mantle rock moves upwards, less material is pushing down on it and the pressure decreases. The rock is under lower pressure; this lowers the melting temperature of the rock and so it melts.

Detailed explanation-4: -Because the temperature of the mantle is fairly constant, a decrease in pressure is the most common cause of magma formation. Magma often forms at the boundary between separating tectonic plates, where pressure is decreased.

Detailed explanation-5: -At ocean–ocean and ocean–continent convergent boundaries, the older/colder/denser oceanic plate sinks into the mantle. This is called subduction. The subducting oceanic plate carries water into the mantle. This water lowers the melting temperature of the rocks in the mantle and creates magma.