Partial melting processes in the Earth’s upper mantle

Abstract

The mantle of the Earth is an essentially solid shell separating the metallic and partially molten core from the cooler rocks of the crust. Extending to a depth of some 2900 km, it accounts for 83% of the Earth’s volume and 67% of its mass. It can be subdivided into two main seismic regions that are broadly concentric with the surface; the upper mantle and lower mantle, separated by the 670 km seismic discontinuity (Fig. 3.1). In this chapter we shall focus our attention on the physical state, chemical composition, mineralogy and partial melting behaviour of the upper mantle. Everything that happens at the surface of the Earth — the building of mountain ranges, the formation of ocean basins, volcanism and even changes in sedimentation patterns — is a response to events taking place within this part of the mantle. In addition, this is also the zone in which the driving forces that move the lithospheric plates about the surface of the Earth originate.