THE OLIGOCENE-MIOCENE COOLING AND EXHUMATION OF A CORDILLERAN METAMORPHIC CORE COMPLEX: NEW APATITE, ZIRCON, AND TITANITE (U-TH)/HE THERMOCHRONOLOGY FROM THE RUBY MOUNTAINS, NEVADA

Cordilleran metamorphic core complexes expose large and relatively complete cross sections of the crust, and as such provide unique windows into a number of geologic processes operating during orogenesis including deformation, magmatism, and metamorphism. Because core complexes expose both deep- and shallow-crustal rocks, they can help provide a complete picture of the temporal evolution of the entire crust. The Ruby Mountains – East Humboldt Range – Wood Hills metamorphic core complex (REHW) in northeastern Nevada exposes an unusually complete upper- to deep-crustal section and records a long and complicated geologic history. This study, which focuses on the Ruby Mountains region of the complex, is part of a larger effort to document the transition from Mesozoic crustal shortening to Cenozoic extension in the Cordillera using multiple low- and medium-temperature thermochronology on samples from multiple crustal levels from throughout the REHW.

New apatite, titanite, and zircon (U-Th)/He thermochronology from the Ruby Mountains suggest cooling and exhumation during the late Oligocene and Miocene. Samples from the Lamoille Canyon and Harrison Pass regions are consistent with multiple periods of exhumation. Apatite (U-Th)/He [AHe] from Lamoille Canyon average ~14 Ma, with some samples exhibiting positive date-eU correlations. Zircon and titanite (U-Th)/He dates [ZHe and THe, respectively] from the same samples yield dates of ~19 Ma, suggesting that this region of the Rubies cooled from >180°C to <65°C between 19-14 Ma. Farther south in Harrison pass, ZHe and THe dates are generally older and range from 29 – 16 Ma, with some samples exhibiting negative date-eU correlations. The previously published thermochronology, ongoing research farther north in the range, and thermal modeling of the thermochronology data from multiple locations throughout the core complex suggests complex patterns in both the timing and style of deformation in the REHW.