Assessing the role of thermal disequilibrium in the evolution of the lithosphere-asthenosphere boundary: An idealized model of heat exchange during channelized melt-transport

Abstract. This study explores how the continental lithospheric mantle (CLM) may be heated during channelized melt transport when there is thermal disequilibrium between (melt-rich) channels and surrounding (melt-poor) regions. Specifically, I explore the role of disequilibrium heat exchange in weakening and destabilizing the lithosphere from beneath as melts infiltrate into the lithosphere-asthenosphere boundary (LAB). During equilibration, hotter-than-ambient melts would be expected to heat the surrounding CLM, but we lack an understanding of the expected spatio-temporal scales and how these depend on channel geometries, infiltration duration, and transport rates. This study utilizes a 1D model of thermal disequilibrium between melt-rich channels and the surrounding melt-poor region, parameterized by the volume fraction of channels (Φ), relative velocity across channel walls (vchannel), channel spacing (d), and timescale of episodic melt-infiltration (τ). The results suggest that, during episodic infiltration of hotter-than-ambient melt, a steady-state 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 a material dependent velocity, reaching a maximum steady-state width δ ~ [Φvchannel (τ / d)2]. 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. For geologically-reasonable values of Φ, vchannel, d, and τ, disequilibrium heating within the TRZ may contribute at least 10−3 W/m3 to the LAB heat budget.