GRAVITY DATA INCONSISTENT WITH AN ASYMMETRICAL BASIN ABOVE THE CASTLE CLIFF DETACHMENT, UTAH AND NEVADA

The Castle Cliff detachment is the easternmost of three generally west-dipping low-angle normal faults that together are inferred to accommodate 54 ± 10 km of west-southwest directed Miocene crustal extension between the Beaver Dam Mountains, Utah and the Meadow Valley Mountains, Nevada (Axen et al., 1990). Given that the present dip of the detachment is only 11°, the sedimentary basin in its hanging wall is expected to be asymmetrical, with the thickest fill close to the western edge.

Gravity data acquired in Beaver Dam Wash and across the Beaver Dam Mountains in May-June, 2010, along the line of a published regional cross-section, greatly increase the resolution of available gravity coverage (Langenheim et al., 2001). A notable feature of the negative Bouguer anomaly for the basin is that it is symmetrical, a pattern that is consistent with the presence of one or more high-angle normal faults on both sides of the basin. A positive Bouguer anomaly beneath the eastern portion of the wash, but west of the front of the Beaver Dam Mountains, is inferred to represent either a rider block or a buried landslide of crystalline rocks. Seismic reflection data obtained across the eastern margin of the basin are currently being processed, with the expectation that they may shed additional light on the dip of the range-bounding fault.