THE ROLE OF THE ~ 16 -5 MA KNOLL- EAST HUMBOLDT-RUBY MOUNTAINS FAULT SYSTEM IN THE EVOLUTION OF THE RUBY–EAST HUMBOLDT-WOOD HILLS METAMORPHIC CORE COMPLEX, NORTHEAST NEVADA

Much of the exhumation of metamorphic rocks in the Ruby Mountains-East Humboldt-Wood Hills metamorphic core complex is commonly ascribed to the ~ 16 to 8 Ma west-dipping Ruby-East Humboldt detachment, whose northernmost known extent is in the vicinity of Wells, Nevada. However, integration of structural and chronologic data from Miocene faults and basins bounding the core complex with data from the Knoll Mountain region due north of the core complex indicate the Ruby-East Humboldt detachment formed part of a much larger, > 190 km long, fault system that included the Knoll Mountain fault. This fault system, the Knoll-East Humboldt-Ruby fault system, extended north of the core complex to Contact, Nevada where it terminated near the southern margin of the Snake River Plain.

New tephrochronology from synextensional basin fill and geologic mapping of the Knoll Mountain segment of the Knoll-East Humboldt Ruby fault system reveals that the fault system as a whole was active from 17-16 to 8 - 5 Ma and involved the development of a late-stage, segmented intrabasin fault system between ~8 and 5 Ma. Moreover, the footwall of the Knoll-East Humboldt Ruby-fault system formed a regional horst bounded on the east by the coeval east-dipping Thousand Springs fault system.

In summary, our synthesis indicates that the Ruby-East Humboldt detachment extended well beyond the confines of the core complex as part of the Knoll-Ruby-East Humboldt fault system whereby the central part of the fault system facilitated exhumation of metamorphic rocks in the core complex. Furthermore, this fault system was active for a longer time than previously recognized. Specifically, our data and synthesis indicates that the Knoll-Ruby-East Humboldt fault system and intrabasin faults, at least north of the Ruby Mountains, ceased to be active sometime after 8 Ma but before 5 to 3 Ma.