9219939 Wernicke BARGE is an integrated, multi-disciplinary investigation of a region of the earth's continental lithosphere where an abrupt boundary exists between highly extended terrain and a tectonically stable block. The main research objective of this study is to use the "natural experiment" of a large strain gradient in the uppermost part of the lithosphere to understand how the Moho and other deep discontinuities respond to extension, thus quantifying how large horizontal strains of the lithosphere relate to vertical motions at various levels, controlled by isostasy. A number of such regions have been identified by geological mapping in the Basin and Range province. Of these, the western margin of the Colorado Plateau is the best suited example for accomplishing our objective. It has the virtues of (1) abruptness; (2) a geologic setting that indicated a simple pre-extensional crustal structure; (3) a well-understood large-scale extensional kinematic history; and perhaps most importantly, (4) a large inland waterway suitable for deep geophysical studies, Lake Mead, that transects the boundary in precisely the location where geological studies can place bounds on crustal uplift during extension. The Principal Investigators are integrating geological and geochronologic studies, marine multi-channel seismic reflection profiling, coordinated land and marine seismic refraction profiling, and gravity modeling to unravel the kinematic and dynamics of the lithosphere's response to severe extensional strain. The main objective of the geologic portion of the BARGE project are nearing completion. The primary objective was to characterize the large-scale pre-extensional configuration of the Gold Butte structural block in the crust through geologic mapping, a petrologic and thermochronometic studies, and paleomagnetic studies of the Proterozoic crystalline basement that comprises the bulk of the block. The geophysical component of BARGE was fun ded a year later than the geological portion. Due to unforseen logistical delays, the geophysical experiment will be conducted in early 1994, nearly a year after the expiration of the grant for the geological portion of the research. This project involves a modest continuation of geological portion of BARGE with two principal objectives: 1) Additional geologic mapping of the Gold Butte and neighboring small fault blocks, in particular the uppermost part of the block where major upper crustal fault zones intersect the high-resolution reflection lines; 2) Participation of the PI in the geophysical experiment, including interpretation of results and preparation of manuscripts for publication. ***
