Melting Behaviour of Mantle Peridotites and Compositional Variations of Partial Melts at High Pressures

Abstract

Determination of composition of melts formed by partial melting of peridotite at high pressures is important for understanding genesis of magmas in the upper mantle; however, the previous experimental studies had more or less shortcoming in the method and the results were not always satisfactory. Recently, a new method which seems to have less shortcoming than the previous methods was developed independently by two groups. In the new method, aggregates of diamond grains are placed on top of or between peridotite layers. Upon heating partial melts formed in the peridotite layers segregate into pore space between diamond grains, and after quencheing they can be analysed without quench problem (Johnson and Kushiro, 1992; Kushiro and Hirose, 1992, Baker et al., 1992; Hirose and Kushiro, 1993, Baker and Stolper, 1993). In the present studies, this method is applied to (1) equilibrium partial melting of a relatively fertile mantle peridotite, (2) stepwise fractional melting of the peridotite, and (3) melt segregation from the peridotite. The compositional variations of melts formed by these processes are determined.