THE PRE-MIOCENE REGIONAL EXHUMATION HISTORY OF DEEP CRUST EXPOSED IN THE RUBY MOUNTAINS METAMORPHIC CORE COMPLEX, NEVADA

Plutonic rocks exposed in the Basin and Range province are known to have experienced widespread extension and uplift at ca. 16.5 Ma. This extension is broadly coincident with timing of earliest volcanism of the Yellowstone hotspot (notably in the Northern Nevada rift and Oregon-Idaho graben and manifest by widespread basalts of the early Columbia River basalt province). Although the coincidence in timing leads to suggestions of a causal relationship, the overall magnitude and history of pre-early Miocene cooling and exhumation is unclear, as most published studies in central and eastern Nevada focus on volcanic rocks and low temperature (<200°C) thermochronometers. Published thermochronologic data bearing on the higher temperature, pre-early Miocene history of the Ruby Mountains (principally K/Ar and ⁴⁰Ar/³⁹Ar hornblende and biotite ages) is insufficient to provide an unambiguous evaluation of the early exhumation history of the Rubys. It is critical to understand the pre-early Miocene exhumation history of this region in order to properly evaluate the influence of the Miocene Yellowstone hotspot. Samples were collected from traverse and longitudinal sections of the Ruby Mountains metamorphic core complex for single-crystal ⁴⁰Ar/³⁹Ar dating, with emphasis on alkali feldspar and muscovite, in order to provide new constraints to the ca. 450-200°C thermal history of deep crustal sections presently exposed in the Rubys. Samples are presently undergoing preparation for analysis in the ANIMAL facility, that include relatively undeformed, euhedral muscovite phenocrysts up to 2 mm in diameter that were collected from post-kinematic granitic intrusives. This study aims to produce in situ laser ⁴⁰Ar/³⁹Ar age dates of muscovites and feldspars from the samples collected in the Ruby Mountains. Due to diffusion of argon in these crystals during cooling, age ranges can be expected to produce core-rim variations in single crystals, and the data collected can be used to further constrain cooling histories of the area and formulate a more complete time-temperature model which could explain the history and crustal evolution of the Ruby Mountains from the Mesozoic to ca. 16.5 Ma. The new data will provide new context to the relationships between extension in northeastern Nevada and the inception of the Yellowstone hotspot.