An experimental investigation of the interactions between reaction-driven and stress-driven melt segregation: 1. Application to mantle melt extraction

Abstract

[1] We present results from experiments designed to investigate the interactions between stress-driven melt segregation and reaction-enhanced melt infiltration, two mechanisms that have previously been studied independently of each other. A melt source (with a melt fraction below the rheologically critical melt fraction) in which the basaltic melt is either orthopyroxene-saturated or orthopyroxene-undersaturated was coupled with a nominally melt-free olivine + orthopyroxene sink in two cylindrical configurations deformed in torsion. As melt migrates from the source to the sink in samples with an orthopyroxene-undersaturated melt source, the basalt dissolves orthopyroxene and precipitates olivine. The local increase in melt fraction during this process increases permeability and enhances melt infiltration. As melt migrates from the source to the sink in samples with an orthopyroxene-saturated melt source, the reaction described above does not occur. These samples display modest infiltration associated with combined surface tension-driven flow and mechanical segregation. Our experiments demonstrate (1) that combined reaction and deformation leads to greater infiltration of melt than does either mechanism alone, and (2) that melt segregation associated with deformation is an effective way to create perturbations in melt fraction along the source-sink interface, which act as nucleation points for reaction-enhanced infiltration in the experiments.