THERMOCHRONOLOGIC CONSTRAINTS ON THE COOLING AND EXHUMATION OF THE NORTHERN RUBY MOUNTAINS, NEVADA
New low temperature, (U-Th)/He thermochonometer data from apatites and zircons from the Ruby Mountains suggest cooling through >180°C to <70°C during the mid-Miocene, ~17 Ma. These samples come from a ~6 km east-west transect across an extensional mylonitic shear zone and metamorphic core complex. Samples were taken primarily from the abundant late-Cretaceous to mid-Cenozoic leucogranites found throughout the complex. Our data records a late-Oligocene to early Miocene cooling and exhumationl history with zircon (U-Th)/He dates ranging from 23.5 ± 0.7 to 12.1 ± 0.8 Ma while apatite (U-Th)/He dates range from 18.5 ± 1.3 to 14.2 ± 0.7 Ma. Complimentary to the previous low temperature themochronometer findings farther south in the Ruby Mountains, our data suggests rapid exhumation along a normal fault from 17 – 16 Ma, however our results from the northern Ruby Mountains are consistent with a more shallow fault system than indicated farther south. These results imply complex fault system activity throughout the Rubies during the mid-Miocene. Ongoing work integrating these results with higher temperature thermochronometry, as well as with similar studies throughout the entire core complex, are consistent with this complex picture.