Relative Timings of Structures and Mesozoic-Cenozoic Intrusions in the Sand Springs Range, Nevada
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The Sand Springs Range (SSR) in western Nevada exposes Mesozoic – Cenozoic structures of the eastern Sierra Nevada, Luning-Fencemaker Thrust Belt, Basin and Range province, and Walker Lane. Recent 1:8000-scale geologic mapping in the northern Sand Springs Range reveals key cross-cutting relations between structures and diverse Triassic – Tertiary igneous rocks. The northern SSR was previously mapped by Page (1964), Willden and Speed (1974), and Satterfield (2005). Our recent mapping includes: locating contacts with GPS and satellite imagery, constructing a grid of tied cross-sections, and sampling and distinguishing seven different igneous map units. Schlumberger’s Petrel software will be used construct a three-dimensional model from the geologic map and cross-section grid. Mapping provides four key timing constraints. First, Sierran (D1) axial-planar cleavage (S1) deforms Triassic quartz porphyry intrusions. Second, Cretaceous granitoid units cross-cut S1 and D1 folds and postdate movement on low-angle faults. Third, a basaltic extrusive previously mapped as Jurassic must be Tertiary because it overlaps Cretaceous granite and is interstratified with Tertiary ash flow tuff. Fourth, Tertiary and Cretaceous sills that locally terminate at a low-angle fault actually post-date faulting: they thicken upward below the fault, only terminate below the fault, and rare Tertiary dikes of the same composition cross-cut the fault. The low angle fault provided a barrier for magma ascent. Cross-cutting relations described are significant because they can be subtle, they overturn previously published sequences of events, and they constrain regional deformation timing. This project was supported by a SW AAPG research grant.