NUMERICAL-MODELS OF A SUBSIDENCE MECHANISM IN INTRACRATONIC BASINS - APPLICATION TO NORTH-AMERICAN BASINS

McKenzie's model of sedimentary basin evolution and its modification, widely used in geophysics, sometimes fails to explain discrepancies be tween predicted and observed values of extension, thinning and subside nce of the Earth's crust, as for the North Sea. We develop a numerical model of sedimentary basin evolution based on the mechanism suggested by Lobkovsky. In the course of rifting, accompanied by thinning of lo wer parts of the lithosphere, the roof of the underlying asthenosphere moves upward. The material of the mantle lifts and partially melts ow ing to the reduction of pressure. The density difference between the m elt and the crystalline skeleton results in the filtration of the ligh ter melt and its accumulation in the form of a magmatic lens. Due to c hanged P-T conditions, the material of the lens undergoes the gabbro-e clogite phase transformation. The resultant anomalously heavy eclogite lens sinks in the surrounding material. This induces a viscous flow, changing the surface topography and forming a sedimentary basin. We co nstruct a 2-D numerical model describing a viscous flow induced by sub sidence of a heavy body and compute changes of surface topography. To compute the flow we employ the Galerkin-spline approach, with modifica tions allowing for density discontinuities and time dependence of the phase transformation. We apply the model to the cases of the Illinois, Michigan and Williston basins. The computed and tectonic subsidence c urves agree well for these cases. The proposed model is compatible wit h the seismic structure of the crust and upper mantle below these basi ns. The model is also consistent with gravity data. The approach is ap plicable to other intracratonic basins.