TESTING DEEP BURIAL OF THE RUBY MOUNTAIN-EAST HUMBOLDT RANGE METAMORPHIC CORE COMPLEX, NORTHEAST NEVADA, VIA STRUCTURAL AND THERMAL RECONSTRUCTIONS OF THE ADJACENT RANGES

The kinematic evolution of the crust within high-elevation orogenic plateaus provides insights into mechanisms of crustal thickening and plateau collapse. The North American Cordillera at the approximate latitude of northeast Nevada experienced Middle Jurassic to early Cenozoic E-W contractional deformation during eastward subduction of the Farallon plate along the western margin of North America. Protracted crustal shortening lead to the formation of the hypothesized high-elevation Nevadaplano. Structures that helped to accommodate thickening of the crust to >50 km are poorly resolved within the Cordilleran hinterland. The Ruby Mountains-East Humboldt Range (REH) metamorphic core complex, northeastern Nevada, consists of a 10–15km thick Neoproterozoic–Triassic passive margin sequence that yields geobarometric data (7–10 kbar) suggestive of deep intra-orogen burial (26–38 km depth) in the Late Cretaceous. The geology in surrounding ranges provides a record of relatively low-magnitude crustal shortening, with no evidence of intracontinental subduction. The core of the REH is strongly deformed and migmatitic, which makes systematic palinspastic reconstructions impossible. Instead, this study focuses on the relatively undeformed ranges along the margins of the REH (Toano-Goshute Mountains, Pequop Mountains, Spruce Mountains, Maverick Springs Range, and the southern Ruby Mountains). We integrate detailed geologic mapping, regional structural restorations, and Raman spectroscopy on carbonaceous material thermometry to place constraints on the geometry, kinematics, and thermal structure of the adjacent ranges. This, in turn, resolves the viability of deep burial of the REH. Important observations show: (1) shortening structures are moderate-low in magnitude with ≤4 km throw; and (2) temperature-depth relationships record a regionally elevated, but continuous, thermal gradient (>40 °C/km), which is inconsistent with deep burial models (≤20 °C/km). Preliminary results show no evidence for large magnitude burial of the upper crust, suggesting limited thickening of the Cordilleran hinterland. Conflicting paleodepths suggest that high geobarometric pressures throughout the REH may reflect non-lithostatic conditions or complications in assessing metamorphic phase equilibria.