Abstract

The composition of magmas erupted at the surface are strongly dependent on the dynamics of melt transport through the mantle. Holistic modelling of melt transport processes requires consistent coupling of the thermodynamics of melting and melt-rock reaction, and geodynamics. However, the high-dimensionality of such coupled problems presents a major theoretical and computational challenge. In this talk I will present a new thermodynamically consistent and tractable framework for integrating multicomponent thermodynamics and multiphase geodynamics.

A major question in terrestrial magmatism is how mid-ocean ridge basalts sustain disequilibrium with the uppermost mantle. This is generally explained by melt transport through high-porosity channels, which are thought to be formed through a reactive channeling instability. However, there remains significant questions about how and where channelisation is initiated. Here I apply our new theoretical and software framework, and present a series of 2D models to investigate the formation of dunite channels in an upwelling harzburgitic mantle column within the Mg2SiO4-SiO2 binary system. These models are the first to self-consistently incorporate eutectic/peritectic melting into magma dynamics. We find that dunite channels can form via incongruent melting of harzburgite, but only when there is a sustained flux of deep silica-poor melts. I will discuss what this implies about the melting conditions beneath mid-ocean ridges.