DETAILED GEOLOGIC MAPPING AND INTERMEDIATE-SCALE MAP COMPILATION OF THE RUBY MOUNTAINS-EAST HUMBOLDT RANGE METAMORPHIC CORE COMPLEX, NORTHEAST NEVADA, YIELD INSIGHTS INTO MESOZOIC CONTRACTION AND CENOZOIC EXTENSION IN THE NORTH AMERICAN CORDILLERA

The Ruby Mountains-East Humboldt Range-Wood Hills-Pequop Mountains region of northeast Nevada has for decades been the focus of geologic mapping and research to understand the formation and deformational history of metamorphic core complexes in the North American Cordillera. In recent years the Nevada Bureau of Mines and Geology (NBMG) has generated six new 1:24,000-scale geologic maps of the region by NBMG geologists and graduate students, while simultaneously publishing six 1:24,000-scale maps authored by many of the region’s long-time researchers. Detailed geologic map coverage of a key transect of this complexly deformed region now exists, extending from the East Humboldt Range in the west to the Pequop Mountains in the east, allowing for integration of the mapping into a 1:62,500-scale geologic map compilation. This compilation allows for a more complete depiction of the region’s structures, which include Mesozoic contractional features, associated with crustal thickening and the development of the Nevadaplano orogenic plateau, Cenozoic detachment fault systems that accommodated metamorphic core complex exhumation, and Miocene to Quaternary high-angle normal fault systems. The new map compilation includes the integration of decades of geochronology data into a common database and development of regional cross sections. The recent geologic mapping has contributed to fundamental research on the deformational history of the region and resulted in numerous publications on a variety of geologic framework topics. The range of research topics facilitated by this multi-year project include: the timing of Mesozoic contraction in eastern Nevada; estimates of Mesozoic crustal thickness and burial of Paleozoic stratigraphy in the Nevadaplano orogenic plateau; the structural and magmatic setting for Carlin-type gold mineralization; the timing, kinematics, and thermal history of metamorphic core complex exhumation via diapiric upwelling of the middle crust; the application of Raman spectroscopy to evaluate the Mesozoic thermal state of the thickened crust; microstructural analysis of mylonitic fabrics to capture shear dynamics of highly extended terranes; and constraints on the timing of extensional basin formation using detrital sanidine and zircon geochronology.