The Thermal Effects of Pervasive and Channelized Fluid Flow in the Deep Crust

Abstract

Heat advection by upward-migrating fluids in one possible mechanism for elevating temperatures within the earth's crust. Models are presented that compare the thermal impact of a pervasive upward flux of fluids to that of the same flux focused into vertical parallel planar channels. In channelized flow, the average temperature across channels is lower than that of pervasive flow at comparable times in the systems' evolutions. As the channel spacing decreases, the evolution through time and steady state approach that of pervasive flow, with pervasive flow representing the limiting case of zero spacing. When channel spacings are small relative to the length of the vertical flow path, lateral temperature gradients around channels will be very shallow for any geologically reasonable flux. When small fluxes, such as may be generated from pelites undergoing progressive metamorphism, are focused into very widely spaced channels, the resultant temperature increase around channels may be discernable with geothermometry, but lateral temperature gradients around channels will be very shallow. Large sustained fluxes, such as may be produced from subduction zones, can have a large thermal impact without focusing. When such fluxes become focused into widely spaced channels, steep, easily discernable lateral temperature gradients develop around the channels.