Kinetics of melt-rock and melt-rock-fluid interactions in the lithosphere: Critical review of experiments and models of the dissolution of planetary rock-forming silicate minerals in aluminosilicate melts

Abstract

Silicate melts and magmas produced at depth encounter rocks at a variety of temperatures and redox conditions during their ascension towards the surface of planetary bodies. Reactions occur between the magma and surrounding material, but despite their potential importance for the regulation of magmatic differentiation, the rates of such interactions are rarely considered and poorly known. The aim of this work is to review the results of high-temperature experiments and kinetic models for the dissolution of the main rock-forming silicate minerals in aluminosilicate melts, partial melting of the main rock types, and reactions between silicate melts and the principal lithologies composing the lithosphere to set the foundations of a new kinetic model.Available experiments on the dissolution of the main rock-forming silicate minerals in aluminosilicate melts far from equilibrium and with high melt-to-rock ratios demonstrate that dissolution rate is controlled either by diffusional or convective transport rather than surface reaction. In contrast, during partial melting and dissolution of magmatic minerals close to equilibrium or under low melt-to-rock ratio (applicable for reactive porous flow, for example), the overall reaction rate can be controlled by surface reaction.The diffusion-controlled dissolution rate r (mol cm -2 s -1 ) of the main rock-forming silicate minerals in aluminosilicate melts at 1300 ± 50°C and <1 GPa pressure in a system with elevated melt-to-rock ratios (and applicable for melt channelization) can be described by an inverse function of the viscosity of the reacting aluminosilicate melts independent on the silicate mineral composition according to: r = 10 -7 η -0.433 , where η (Pa s) is the reacting melt viscosity. This function implies a simple Si atom detachment mechanism during silicate dissolution in the melts. This equation can be applied to the main rock-forming silicate mineral dissolution during melt-rock interaction processes in the lithosphere such as shallow mantle assimilation, at pressures up to 1 GPa. The broad negative correlation between dissolution rate and the reacting melt viscosity demonstrates that lowviscosity mafic-ultramafic magmas are far more prone to contamination by lithosphere materials than high viscosity felsic magmas. An expanded database for the main rock-forming silicate minerals at higher pressure-temperature conditions may be directly applicable for lithosphere assimilation by planetary magmas, magma mixing as well as modeling of diverse types of melt-rock interaction.