Basin and Range Geoscientific Experiment (BARGE)

This project involves an integrated, multi-disciplinary investigation to quantify how the deep continental crust and uppermost mantle respond to extension, and to thus establish how large horizontal strains of the lithosphere relate to vertical motions controlled by isostasy. The principal investigators plan to use the "natural experiment"of a large strain gradient in the uppermost part of the lithosphere associated with the abrupt boundary between highly extended terrain and a tectonically stable block. They have chosen the western margin of the Colorado Plateau to study. It is ideally suited for accomplishing their research objectives for several reasons: (1) the transition is particularly abrupt here; (2) the geologic setting indicates a simple pre- extensional crustal structure; (3) it has a well-understood large- scale extensional kinematic history; (4) the large inland waterway of Lake Mead provides a unique environment in which to perform deep geophysical studies that transect the boundary in precisely the location where geological studies place bounds on crustal uplift during extension. They propose to integrate geological and geochronologic studies, "marine"multi-channel seismic reflection profiling in the lake itself, integrated with land-based recordings on an array on three-component seismometers to provide control on seismic velocity structure and to develop tomographic images of the region which, together with gravity modeling will allow them to unravel the kinematics and dynamics of the lithosphere's response to severe extensional strain.