Olivine crystallographic control and anisotropic melt distribution in ultramafic partial melts

Abstract

In the upper mantle, physical properties (permeability, electrical conductivity, and seismic velocity) are highly dependent on the melt geometry. Both flat and curved melt interfaces exist in olivine-basalt partial melts. To further understand anisotropic wetting behavior of partial melting within the mantle, crystal orientation studies have been conducted to determine the Miller indices of flat interfaces, wetted by the melt in olivine-basalt partial melt samples. The samples were equilibrated at pressures of 1-2 GPa, and temperatures of 1350-1400 °C for 142-549 hours. Crystal orientation studies show that lower Miller indices of crystals are associated with wetted-flat melt interfaces and melt films. Specifically, (010), (110), and (021) olivine faces in these studies were dominantly wetted, indicating that they may be potentially large contributors to permeability and seismic anisotropy in the upper mantle where partial melts occur with high degrees of preferred crystallographic alignment.