Geologic Mapping of the Pequop Mountains, NE Nevada: Exploring Basic and Applied Topics in the Easternmost Ruby Mountains-East Humboldt Range Metamorphic Core Complex
Abstract
The Ruby-East Humboldt core complex and surrounding ranges in NE Nevada record an enigmatic history of Mesozoic contraction and Cenozoic extension. The Pequop Mts in the eastern part of this system expose a continuous section of Neoproterozoic-Permian sedimentary rocks; numerous small Jurassic, Cretaceous, and Eocene intrusions; Eocene volcanic rocks; Miocene sedimentary rocks; and Quaternary basin deposits. Preservation of the Paleozoic section and exposure of Mesozoic thrust faults and foliations make this area ideal for investigating the overprinting Mesozoic-Cenozoic tectonic evolution of NE Nevada. USGS STATEMAP supported mapping builds upon prior research to address basic (characteristics and timing of major contraction, metamorphism, and extension) and applied (origin of Carlin-type gold deposits) geology. Mesozoic contraction and Cenozoic extension divided the range into several structural blocks. Mapping reveals similarities and differences in Paleozoic facies between blocks, reflecting both local facies variation and tectonic transport. Contraction and metamorphism have been attributed to either the Jurassic Elko or Cretaceous Sevier orogenies, but intrusion of probably Jurassic lamprophyre along a major thrust suggests it and folding are Jurassic. Furthermore, a continuous metamorphic gradient from amphibolite grade Cambrian rocks to non-metamorphosed Permian rocks in the lower plate of the thrust raises questions about interpretations of overlying thrust plates that buried rocks to great depths and pressures. Cenozoic extension and tilting are constrained by 40°E dipping 41-39 Ma volcanic rocks and underlying Paleozoic rocks. The concordance of these volcanic rocks with uppermost Paleozoic rocks preclude major pre-41 Ma extension. W-dipping faults along the range's west side accommodated extension since middle Miocene, based on thick deposits of that age containing megabreccia of footwall rocks. Late Pleistocene scarps along the range-front fault demonstrate active extension. Late Pleistocene lakes occupied adjacent valleys. A Carlin-type deposit in the E side of the range may have formed in the Eocene but was likely controlled by Jurassic structures. Its occurrence greatly expands the geographic and geologic setting of these significant deposits.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.V31F0186H
- Keywords:
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- 8110 Continental tectonics: general;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICSDE: 8178 Tectonics and magmatism;
- TECTONOPHYSICSDE: 8486 Field relationships;
- VOLCANOLOGY