Cretaceous–Neogene structural architecture, normal faulting, and sedimentary basin development in the Ruby metamorphic core complex domain, northeast Nevada, USA

The Ruby metamorphic core complex domain encompasses an ∼10,000 km2 area that includes the Ruby Mountains, East Humboldt Range, Wood Hills, Windermere Hills, and Pequop Mountains in northeast Nevada, USA. The domain contains metamorphic and mylonitized mid-crustal rocks that were exhumed by an intricate array of poorly understood Late Cretaceous−Cenozoic normal faults. This study establishes the first holistic structural architecture and sequence of normal faulting in the Ruby metamorphic core complex domain. The architecture and sequence of faulting are established by synthesizing new and published geologic mapping, and geochronology and sedimentology of synextensional basin fill. Our synthesis shows that after Mesozoic thrust faulting via the Windermere-Angel Lake and Independence thrusts, including a period of Barrovian metamorphism, the core complex sustained four phases of exhumation accommodated by normal faulting. The first phase of normal faulting produced the top-to-the-west to -northwest Pequop fault and was active at some time between 84 Ma and 41 Ma. The second phase began between 38 Ma and 35 Ma and was accommodated by the newly recognized, top-to-the-northwest Ruby-East Humboldt (REH)-Holborn fault. The REH-Holborn fault was a rolling-hinge-style, ductile-to-brittle normal fault that created a synextensional basin filled with sediment of the Clover Creek formation from at least 35−17 Ma. Basin filling was followed by the extinction of the fault between 17 Ma and 15 Ma. The third phase of exhumation was accomplished by N-striking horst-and-graben−style normal faults of the 16 Ma to >3 Ma east-dipping Thousand Springs and west-dipping Knoll-Ruby fault systems, whose synextensional basins filled with sediment of the Humboldt Formation. The modern range-bounding normal faults are accomplishing the fourth and ongoing phase of exhumation. This study has implications for previous work that attributes high pressures recorded by metamorphic rocks to tectonic overpressure in that it shows that significant thrust faulting was a prominent contributor to the development of high pressures. Moreover, this study shows that significant Eocene−Oligocene exhumation of mid-crustal rocks−−previously attributed to diapirism in the absence of regional extension−−occurred during extension and was accommodated by the REH-Holborn normal fault. This indicates that diapirism was not the primary mode of exhumation.