Mantle

Definition

The mantle is the part of the Earth or of other planets between the crust and the core. On Earth, it is mainly composed of silicate minerals, whose nature changes depending on the pressure (or depth). In the upper mantle, between the base of the crust and the transition zone at about 660 km, the principal rock type is peridotite composed of olivine, orthopyroxene, clinopyroxene, and an aluminous phase (plagioclase, spinel, or garnet). In the lower mantle, these minerals convert to denser phases such as Mg- or Ca-perovskite and magnesiowüstite. The terrestrial mantle is solid except in shallow zones of partial melting beneath mid-ocean ridgesor in hot spots, and perhaps at the core-mantle boundary. The mantle convects at different scales, one manifested by the relative motion of lithospheric plates, the other by the upwelling of mantle plumes from the mantle-core boundary (D″ zone) or from the upper-to-lower mantle boundary at 660 km depth. The occurrence of mantle...