Geometry of Basement-Cored Structures Using Reasonable Rheological Models for Basement Deformation in Wyoming Province: ABSTRACT

Abstract

Direct observations of the material behavior of both basement and sedimentary-cover rocks reveal that we may be able to relax the assumption that basement rocks deform rigidly and that cover rocks behave passively. Basement rocks, which lack mechanical anisotropy (e.g., no foliation, layering), may deform by faulting along narrow, discrete faults or along zones of faulting, which may be several kilometers wide. Both high-angle and low-angle faults are compatible with a general model of regional horizontal compression. Low-angle faults, in particular, may require internal deformation of the basement rocks. Based on limited data from surface mapping and/or subsurface data, it is possible to construct a number of plausible geometric models for the configuration of the basement. The resultant cross sections must balance either locally or regionally using both volume and line length in the sedimentary-cover rocks and using volume of the basement rocks and line length for the upper basement surface. Any of these geometric models has the possibility of depicting the true basement configuration and can be tested with selected additional data. Sequential restoration of the cross sections provides useful information about the relative timing for development of structures in both the cover rocks and the basement. Knowledge ofmore » timing (e.g., early out-of-syncline crowd vs. late mountain-flank thrusts) can be used in forward modeling and aids in exploration by accepting or rejecting certain specific cross sections without the need for additional subsurface data.« less