Assessing the role of thermal disequilibrium in the evolution of the lithosphere-asthenosphere boundary: An idealized model of heat exchange during channelized melt-transport
- Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87106, USA
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.
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