EXTENSIONAL AND STRIKE-SLIP FAULTING INTERACTIONS IN THE NORTHERN SIERRAN – GREAT BASIN TRANSITION ZONE INFERRED FROM NEW INTEGRATED GRAVITY DATA

Basin geometries visualized from recently integrated gravity data suggest interactions between extensional and strike-slip fault systems in the northwestern Great Basin. These interacting fault systems may have accommodated late Cenozoic westerly to northwesterly relative displacement of the Sierran Block. More than 1100 new stations near Reno, over 1000 previously unincorporated stations from published surveys, and 3900 stations from the National Geodetic Survey's gravity database were combined to form a new compilation that elucidates structural features in the transition zone between Carson Valley and Honey Lake. Gravity defined basin geometries in the transition zone show a discontinuous but well defined series of north-trending, 500 to 1500 meter deep grabens. This zone consists of several subparallel basins over a width of 20 to 40 km in the Great Basin and a prominent end-member - the Lake Tahoe basin - within the Sierran block. The north-trending pattern of basins terminates abruptly northward against the inferred trace of the Walker Lane zone between Pyramid and Honey Lakes signifying a possible kinematic relation between northwest-striking dextral faults in the Walker Lane and the northerly striking normal faults. The relatively deep Honey Lake basin appears to have developed between two northwest-striking strands of the Walker Lane, with faults on the southwest and northeast basin margins accommodating a significant component of normal offset. Ongoing studies are integrating these observations with geologic field relations.