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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, B06414, doi:10.1029/2006JB004663, 2007

Continental thermal isostasy: 1. Methods and sensitivity

Derrick Hasterok

Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, USA


David S. Chapman

Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, USA


Abstract

Continental elevations result from a combination of compositional and thermal buoyancy and geodynamic forces. Thermal effects are often masked by compositional variations to crustal density and thickness that produce equal or greater relief. We have developed a method by which compositional variations in the crust may be removed, thereby isolating the thermal contribution to elevation. This isostatic correction normalizes the composition of a region to a standard crustal column 39 km thick having an average density of 2850 kg m−3. The crustal thickness and density are computed using one-dimensional seismic V P models and an empirical velocity to density conversion. Continental regions adjusted for compositional effects show that thermal isostasy can produce nearly 3 km of relief between cold shield platforms and hot rift zones, comparable to observed relief between young (hot) and old (cold) regions of oceanic lithosphere. A Monte Carlo analysis is used to estimate the uncertainties in the isostatic correction. Uncertainties in the seismic parameters, surface heat flow, and regression coefficients of the velocity-density relationship are all incorporated into the analysis. The Wyoming Craton is used as a case study to demonstrate the effectiveness of the elevation adjustment. Analyses of seismic V P models yield a crustal thickness of 49.5 ± 4.9 km and density of 2945 ± 13 kg m−3. The computed compositional correction to elevation for the Wyoming Craton is −131 ± 180 m, shifting the raw elevation of 1069 m to an adjusted elevation of 938 m.

Received 28 July 2006; accepted 22 February 2007; published 23 June 2007.

Keywords: thermal isostasy; continents; elevation.

Index Terms: 5405 Planetary Sciences: Solid Surface Planets: Atmospheres (0343, 1060); 1020 Geochemistry: Composition of the continental crust; 3010 Marine Geology and Geophysics: Gravity and isostasy (1218, 1222); 8107 Tectonophysics: Continental neotectonics (8002); 8103 Tectonophysics: Continental cratons.

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Citation: Hasterok, D., and D. S. Chapman (2007), Continental thermal isostasy: 1. Methods and sensitivity, J. Geophys. Res., 112, B06414, doi:10.1029/2006JB004663.