HR: 0800h
AN: T31C-0577    [Abstracts]
TI: The Mormon Peak and Tule Springs Detachments of Southern Nevada and Their Role in Interpreting the Subsurface Structure of the Sevier Desert Basin
AU: * Wernicke, B
EM: brian@gps.caltech.edu
AF: California Institute of Technology, Division of Geological and Planetary Sciences, Mail Stop 100-23, Pasadena, CA 91125,
AU: Axen, G J
EM: gaxen@ess.nmt.edu
AF: New Mexico Tech, Department of Earth and Environmental Science, Soccoro, NM 87801,
AB: The eastern Sevier front is commonly overprinted by west-dipping normal faults that have been active through much of Cenozoic time. Although examples of disparate age and geometry abound, the Sevier Desert detachment stands out as being: (1) a very large, low-angle structure, (2) probably still active, and (3) at drillable depth, and hence is a prime target for scientific drilling. Among the closest surface-exposed analogs of the detachment are the Miocene Mormon Peak and Tule Springs detachments in southern Nevada, about 250 km SSW of the Sevier Desert. In both areas, the detachments developed within a few km of the basal Sevier thrust. The few traces of the southern Nevada detachments that were identified by reconnaissance mapping in the 1950s were first interpreted as underlying "rootless" gravity-slide masses. Detailed stratigraphic and structural mapping in the 1980s revealed the full extent of these detachments and their close relationship to the basal Sevier thrust. Construction and retrodeformation of cross sections through the two detachments demonstrated that neither fault could represent the base of a surficial slide mass. The key field relationship is the structural contiguity of the hanging walls of the detachments with large mountain range blocks in their down-dip directions. "Rootless" gravity-driven masses of equivalent or larger scale are widely documented, and in contrast to the southern Nevada detachments show clear evidence along their down-dip portions of either riding over the earth's surface (e.g. Heart Mountain, WY; Shadow Valley, CA) or having been internally shortened (e.g. Bearpaw Mountains, MT; Louisiana shelf). A rootless slide origin for the Mormon Peak detachment has been revived based on meso- and microstructural analysis of the fault surface (refs. 1, 2, and 3), but the hypothesis still fails the retrodeformation test at macroscopic scale. The retrodefomed sections indicate that the footwalls of the southern Nevada detachments expose a paleodepth range from near-surface conditions to more than 7 km, which will be useful for comparison with microstructures that are encountered along the Sevier Desert detachment where it is sampled at depth. 1: Carpenter et al., 1989, Geology 17, p. 774; 2: Anders et al., 2006, J. Geol 114, p. 645; 3: Walker et al., 2007, Geology 35, p. 259.
DE: 8109 Continental tectonics: extensional (0905)
DE: 8110 Continental tectonics: general (0905)
DE: 8123 Dynamics: seismotectonics
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: 2007 Fall Meeting