HR: 0800h
AN: T21C-0499    [Abstracts]
TI: Continental Thermal Isostasy
AU: * Hasterok, D
EM: dhasterok@mines.utah.edu
AF: University of Utah Department of Geology and Geophysics, 135 S 1460 E WBB Rm 709, Salt Lake City, UT 84047 United States
AU: Chapman, D S
EM: dchapman@park.admin.utah.edu
AF: University of Utah Department of Geology and Geophysics, 135 S 1460 E WBB Rm 709, Salt Lake City, UT 84047 United States
AB: The sources of continental elevations are partitioned into a combination of compositional, thermal, and geodynamic buoyancy. Because the potential elevation due to crustal compositional variations are large, an isostatic correction normalizing the effect of crustal composition on elevation is applied to reveal the effects of thermal buoyancy. Particular attention is paid to the uncertainties related to removing compositional effects. The elevation of 32 North American tectonic provinces are adjusted for the effect of compositional buoyancy by computing an isostatic adjustment relative to a standard crustal section (average density of 2830~kg/m³ and a 40~km thick crust). The crustal thickness and P-wave seismic velocity (V_P) structure are determined for each province from seismic models; densities are computed using an empirical relationship derived from laboratory pressure-temperature-velocity-density data. Compositional elevation adjustments of North American tectonic provinces range ~-500~m in the southern Rocky Mountains to 2500~m in the Gulf of California, with uncertainties ranging from ~200~m to >600~m. Thermal buoyancy is estimated by integrating the difference between a geotherm derived from observed values of heat flow and a reference geotherm. The best fitting continental heat flow--elevation model has a reference heat flow of 43~mW/m² at 0~km and a 60-40 partitioning of surface heat flow between basal heat flow and upper crustal radioactive heat production. Whereas raw elevations of continental provinces show little correlation with heat flow, the compositionally adjusted elevations show a clear trend with about 3~km difference between cold and hot provinces. A continental heat flow--elevation plot is used to identify outliers in adjusted province elevations. These anomalous elevations may reflect a non-steady state thermal regime, dynamically supported elevation, anomalous mantle or some combination of these states. Discriminating between these sources of elevation provides insights into the geodynamics of North America, and demonstrates the usefulness of this approach in continental geodynamic studies. We extend this method to a set of global tectonic provinces.
DE: 5418 Heat flow
DE: 5475 Tectonics (8149)
DE: 8103 Continental cratons
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8130 Heat generation and transport
SC: Tectonophysics [T]
MN: Fall Meeting 2005