The South Virgin-White Hills detachment (SVWHD) in the central Basin and Range province with an along-strike extent of ∼60 km is a major continental detachment fault system. Displacement on the SVWHD decreases north to south from ∼17 to <6 km. This is accompanied by a change in fault and footwall rock type from mylonite overprinted by cataclasite to chlorite cataclasite and then fault breccia reflecting decreasing fault displacement and footwall exhumation. Apatite fission track (AFT) thermochronology was applied both along-strike and across-strike to assess this displacement gradient. The overall thermal history reflects Laramide cooling (∼75 Ma) and then rapid cooling beginning in the late early Miocene. Age patterns reflect some complexity but extension along the SVWHD appears synchronous with rapid cooling initiated at ∼17 Ma due to tectonic exhumation. Slip rate is more rapid (∼8.6 km/Ma) in the north compared to ∼1 km/Ma in the south. The displacement gradient results from penecontemporaneous along-strike motion and formation of the SVWHD by linkage of originally separate fault segments that have differential displacements and hence differential slip rates. East-west transverse structures likely play a role in linkage of different fault segments. The preextension paleogeothermal gradient is well constrained in the Gold Butte block as 18-20°C/km. We present a new thermochronologic approach to constrain fault dip during slip, treating the vertical exhumation rate and the slip as vectors, with the angle between them used to constrain fault dip during slip through the closure temperature of a particular thermochronometer. AFT data from the western rim of the Colorado Plateau constrain the initiation of timing of cooling associated with the Laramide Orogeny at ∼75 Ma, and a reheating event in the late Eocene/early Oligocene associated with burial by sediments ("rim gravels") most likely shed from the Kingman High to the west of the plateau.
ASJC Scopus subject areas
- Geochemistry and Petrology