Continental thermal isostasy: 1. Methods and sensitivity

摘要

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.