Low-temperature thermochronometric constraints on Cenozoic intraplate deformation in the central Basin and Range

Tandis Bidgoli
University of Kansas, Department of Geology Lawrence, Kansas, USA
[email protected]

The central Basin and Range of southern Nevada and southeastern California has experienced both Miocene extension and Miocene to recent transtension. This unique positioning has made the region instrumental in the development of kinematic and dynamic models for continental rifting and strike-slip faulting. Two classes of competing models have been proposed for the development of low-angle normal and strike-slip faults in the region. One class of models suggests that motion on normal and strike-slip faults is synchronous (e.g., rolling hinge and pull-apart models). The other proposes a two-phase history, with extensional faults being reactivated and/or overprinted by a relatively young phase of strike-slip faulting. We are testing these models through a comprehensive (U-Th)/He thermochronologic study of 15 ranges across the province. 230 samples have been collected from the footwalls of the major normal faults and from step-overs in key strike-slip faults. Preliminary results suggest that extension initiated at ~18 Ma in the eastern part of the province and has migrated westward with time. The youngest cooling ages (4-5 Ma) occur in the very western part of the province and may signal the onset of transtension associated with the developing Eastern California Shear Zone. These Pliocene cooling ages are similar to the inferred timing of mantle delamination in the central and southern Sierras, suggesting that internal or intraplate factors, rather than external controls like plate boundary kinematics, may be dominant.

AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects