Thermal Conductivity of Quartz and Feldspars with Application to Continental Heat Flow

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EAR-0125883HofmeisterA one-year investigation of thermal conductivity (k) of crustal minerals using spectroscopic measurements and modeling is proposed. The data will be supplemented with new measurements of the thermal diffusivity of a plagioclase feldspar using a laser-flash apparatus. These measurements will provide a benchmark of the PI's model for the lattice contribution against available reliable data on thermal conductivity below room temperature for quartz and feldspar, and against the laser flash measurements at high T. The calibrated model will provide high T data appropriate for diffusion of heat in the Earth, and will constrain pressure dependencies through the equation of state. The purpose is to try and understand why the most recent heat flow data from the continents is lower than that from the oceans (Pollack et al. 1993), contrary to the expected correlation of high heat flow with high radioactive contents, and to the partitioning of almost all of Earth's radioactive elements into the crust The imbalance suggests that virtually no heat from the mantle escapes through the crust. From the determination of k(T,P) for quartz and feldspars, the continental crust can be approximated by a conductive cooling model that incorporates internal heating. Requiring that the surface heat flux and temperature be matched will give solutions relating the basal temperature to the radioactive contents. Comparison of results with previous independent estimates of radioactive contents (based on chemical inventory) and of temperatures (based on phase relations) will set limits on these interrelated quantities, and thus on the basal heat flow from the mantle. This result should provide a constraint for convection models of the mantle.