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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, B06415, doi:10.1029/2006JB004664, 2007

Continental thermal isostasy: 2. Application to North America

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 can be partitioned into contributions from thermal and compositional buoyancy and geodynamic forces. In order to isolate the thermal component, elevations of 36 North American tectonic provinces are adjusted for the effects of compositional thickness and density variations by computing an isostatic adjustment relative to a standard crustal section (2850 kg m−3 density and 39 km thickness). Crustal densities are estimated using an empirical velocity-density relationship. Compositional elevation adjustments applied to North American provinces range from ∼−1100 m in the southern Rocky Mountains to 2300 m in the Gulf of California, with uncertainties ranging from ∼200 m to >600 m. Theoretical 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 46.6 mW m−2 at 0 km and a 60:40 partitioning of surface heat flow between reduced and upper crustal radiogenic heat flow. Raw elevations of continental provinces show little correlation with heat flow, while compositionally adjusted elevations show a clear trend with ∼3 km difference between hot and cold provinces. A continental heat flow–elevation plot is used to identify outliers in adjusted province elevations. Anomalous elevations may reflect a nonsteady state thermal regime, dynamically supported elevation, anomalous mantle, or some combination of these states. Discriminating between these elevation sources provides insight into the geodynamics of North America, demonstrating the usefulness of this approach in continental geodynamic studies.

Received 29 July 2006; accepted 22 February 2007; published 23 June 2007.

Keywords: thermal isostasy; continental elevation; North America.

Index Terms: 8178 Tectonophysics: Tectonics and magmatism; 5418 Planetary Sciences: Solid Surface Planets: Heat flow; 8103 Tectonophysics: Continental cratons; 3010 Marine Geology and Geophysics: Gravity and isostasy (1218, 1222); 8110 Tectonophysics: Continental tectonics: general (0905).

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Citation: Hasterok, D., and D. S. Chapman (2007), Continental thermal isostasy: 2. Application to North America, J. Geophys. Res., 112, B06415, doi:10.1029/2006JB004664.