PALEOMAGNETIC RESULTS FROM THE EASTERN CALIENTE-ENTERPRISE ZONE, SOUTHWEST UTAH: IMPLICATIONS FOR INITIATION OF A MAJOR MIOCENE TRANSFER ZONE

Previous paleomagnetic data from the central and western Caliente-Enterprise zone (CEZ), a major east-west trending left-lateral transfer system in southeastern Nevada and southwestern Utah, reveal large-scale counterclockwise vertical axis rotations of strike-slip bounded fault blocks that have experienced map-view domino-style rotation (Hudson et al., 1998). In this study, paleomagnetic data were obtained from Miocene volcanic rocks along the eastern segment of the CEZ in order to test the potential influence of the 22 Ma Iron Axis laccolith complex on the initiation of the transfer zone along the southeastern portion of the CEZ. Data from 38 sites (337 accepted samples) were collected over a ca. 25 km north south transect through the Pine Valley Mountains of southwest Utah. In addition to the Stoddard Mountain laccolith, paleomagnetic data from the Bauers and Harmony Hills ash flow tuffs of the Quichapa Group (23-22 Ma), the 22 Ma Rocks of Paradise and the 19 Ma Racer Canyon Tuff were obtained. The majority of the samples yield a single component magnetization isolated by AF demagnetization that is of high coercivity, although some variation were observed depending on rock type. In the south and east, the Stoddard Mountain laccolith and Miocene volcanics yield site mean demagnetization data that are discordant (<10° cw and ccw) to the Miocene expected direction. In contrast, site mean data from ashflow tuffs to the north and west of the Iron Axis laccoliths exhibit a progressive northward increase in the degree of ccw rotation (up to 60°). Site mean data from the Rocks of Paradise tuff yield anomalous directional data that may represent a transitional field direction. Our mapping shows that NW-SE strike-slip faults are more prominent in areas of greater ccw rotations (i.e., Pinto Quadrangle). The vertical axis rotations identified in the volcanic rocks better define the eastern and southern boundary of the CEZ north of the Iron Axis laccoliths. Our results suggest that the laccoliths inhibited the southward migration of crustal extension in the region, perhaps by acting as a rupture barrier, causing deformation to migrate westward into Nevada (Axen, 1998).