GEOCHRONOLOGIC AND PETROLOGIC CONSTRAINTS ON DEEP CRUSTAL METAMORPHIC CORE COMPLEX DEVELOPMENT, EAST HUMBOLDT RANGE, NEVADA

The Ruby Mountains-East Humboldt Range in northeastern Nevada are the westernmost example of a metamorphic core complex within the hinterland of the Late Cretaceous to early Tertiary Sevier orogenic belt, exposing the oldest rocks in Nevada as well as the deepest western pre-Cambrian basement. The northern East Humboldt Range is unique in the core complexes of the Sevier Hinterland in the depth of its exposure of the ductiley deformed high-grade metasedimentary rocks that underlie the Tertiary mylonitic shear zone. The protracted and complex metamorphic history of continental evolution recorded in these deep crustal exposures is condensed in the key tectonic contact of Paleoproterozoic metapelitics and pre-Cambrian orthogneiss within the core and lower limb of the Winchell Lake fold-nappe (WLN), a south-verging recumbently folded thrust fault. Recent studies have produced potentially conflicting zircon ages within the WLN for early evolution of the core complex, constraining exhumation to a relatively short duration of 2.1 to 6.1 Ma from magmatic conditions at depth recorded in migmatitic orthogneiss to temperatures of ~400 °C.

This study presents petrologic analysis of eleven rock samples of key structural units and garnet amphibolites collected in the Angel Lake cirque. A detailed outcrop-scale map informs the petrographic analysis by characterizing the tectonic relationships recorded of the WLN. In addition, laser ablation split stream (LASS) dating of zircon, titanite, and monazite will help constrain the conditions of the earliest phase of deformation in the East Humboldt Range core complex, potentially constraining the age and duration of exhumation.