Thermal disequilibrium during melt-transport: Implications for the evolution of the lithosphere-asthenosphere boundary

Abstract

This study explores how thermal disequilibrium during melt-infiltration and melt-rock interaction may modify the continental lithosphere from beneath. Using an idealized 1D model of thermal disequilibrium between melt-rich channels and the surrounding melt-poor material, I estimate heat exchange across channel walls during channelized melt transport at the lithosphere-asthenosphere boundary (LAB). For geologically-reasonable values of the volume fraction of channels ($\phi$), relative velocity across channel walls ($v$), channel spacing ($d$), and the timescale of episodic melt-infiltration ($\tau$), model results suggest disequilibrium heating may contribute $>$ $10^{-3}$ W/m$^3$ to the LAB heat budget. During episodic melt-infiltration, a thermal reworking zone (TRZ) associated with spatio-temporally varying disequilibrium heat exchange forms at the LAB. The TRZ grows by the transient migration of a disequilibrium-heating front at material-dependent velocity, reaching a maximum steady-state width $\delta\sim$ $\left[\phi vd^{-2}\tau^{2} \right]$. The spatio-temporal scales associated with establishment of the TRZ are comparable with those inferred for the migration of the LAB based on geologic observations within continental intra-plate settings, such as the western US.