THERMOCHRONOLOGY OF UPPER CRUSTAL ROCKS IN THE WOOD HILLS, NEVADA: DOCUMENTING THE TRANSITION FROM CONTRACTION TO EXTENSION IN THE U.S. CORDILLERA

The metamorphic core complexes of the Basin and Range Province record a long and complex geologic history that includes contraction and crustal shortening followed by extensional deformation and thinning. Many studies using a wide range of methods have attempted to uncover how regional extensional collapse of the crust initiated. Previous work on high temperature processes has documented older, Cretaceous to Eocene (~70 – 34 Ma) deformation, whereas studies of shallower crust (using low temperature thermochronology and basin analysis) highlight more recent, Miocene (~15 Ma) processes. In order to address a major gap in the thermochronologic record across the Ruby Mountains – East Humboldt Range - Wood Hills metamorphic core complex in northeastern Nevada, we are using zircon, titanite, and apatite (U-Th)/He thermochronology within a well-understood structural framework from samples in the Wood Hills to document the cooling and exhumational history of the shallower parts of the core complex. Thermal modeling will also be used to create continuous cooling histories throughout the range which can be compared to deeper parts of the region in order to bridge the gap between datasets.

New zircon (U-Th)/He dates from the Wood Hills record late Eocene to early Oligocene cooling through a zircon He closure temperature of ~180 °C. These results are consistent with previous studies and suggest that cooling related to extensional exhumation in the Wood Hills occurred earlier than has been documented farther west in the core complex. Ongoing thermal modeling will better define the timing and rates of exhumation in the Wood Hills and provide important constraints on the evolution of the entire core complex.