The Fox Range, northwest Nevada
Kinsella, Margaret Elizabeth
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Recent studies indicate an Early Cretaceous strike-slip fault system, the Mojave-Snow-Nevada-Idaho, extended from southeast California through northwest Nevada into western Idaho and accommodated 400-500 km of dextral offset. Younger cover and plutonic intrusions have obscured the fault. Therefore, its location and displacement are based on the juxtaposition of unrelated geologic units. To investigate the western boundary of the proposed fault, the Fox Range in northwest Nevada was extensively mapped. The pre-Cenozoic rocks of the range are divided into four metasedimentary units: a graphitic argillite unit (Smith Canyon argillite), a massive quartzite unit (Cottonwood Canyon quartzite), a quartz-muscovite-schist (Smoke Creek schist), and a quartz-biotite paragneiss (Fox Canyon gneiss), all intruded by Cretaceous plutons and dikes. Two phases of deformation were identified in all units: 1) bedding deformed by tight to isoclinal D1 folds verging west, accompanied by an axial planar foliation (S1); 2) tight to open D2 folds deforming S1 and D1 folds with S2 present locally. These deformational events are not found to the east of the proposed fault in the adjacent Black Rock and Late Triassic back-arc terranes. U-Pb detrital zircon ages were obtained from several samples of quartzite in the Fox Range. The distribution of zircon ages are essentially identical to those of Jurassic erg deposits of the Colorado plateau and their redeposited equivalents in the southwest Cordillera. This indicates the Fox Range is unrelated to neighboring terranes and was translated northwards along the fault system possibly from an origin as far as southwestern Arizona.