Mesozoic Geology of the Sand Springs Range, West-Central Nevada

Mesozoic structures and rock types mapped at a scale of 1:80000 in the Sand Springs Range (SSR), west-central Nevada, differ from those in adjacent allochthons. SSR structures and rock types contrast with those in better-known exposures in the Sierra Nevada to the west and in the Luning-Fencemaker thrust belt to the east. Cenozoic igneous rocks in the SSR are steeply tilted. However all Cenozoic-pre-Cenozoic contacts are fault or intrusive contacts and Cenozoic structures have not tilted or rotated pre-Cenozoic structures. Pre-Cenozoic rocks include: a) greenschist facies tectonites, b) amphibolite facies tectonites, c) unmetamorphosed Jurassic-Cretaceous basalt, and d) post-tectonic, Late Cretaceous granitoid plutons. Tectonites include: carbonate rocks, black slate/schist, felsic and mafic volcanic and volcanogenic rocks, and intrusive rocks. Three Triassic successions, two Jurassic successions, and three successions of unknown, Mesozoic and/or Paleozoic age are recognized within tectonites in individual fault blocks. Most successions can be placed within an overall Triassic-Jurassic stratigraphic section which appears consistent throughout the Sand Springs lithotectonic assemblage, the allochthon or terrane which includes the SSR. Rock types and depositional environments of the Sand Springs assemblage differ fromage-equivalent sections in adjacent allochthons, implying large displacements on bounding faults. Three generations of Mesozoic structures in the SSR, DI, D2, and D3, are distinguished by direct superposition. Middle-Late Jurassic D, structures include map-and outcrop-scale folds, faults, and pervasive metamorphic foliations and lineations of unknown original orientation. Late Jurassic-Cretaceous D2 structures are northeast-trending map- and outcrop-scale folds and low-angle faults. Late Jurassic-Cretaceous D3 structures are northwest-trending, map- and outcrop-scale folds. An angular unconformity separates tectonites deformed only in D, from Jurassic-Cretaceous basalt only deformed in D2 and D3. D2 and D3 structures are characteristic of the LuningFencemaker thrust belt, while D, structures, which predate D2 by a large time span, are possibly correlative to Middle-Late Jurassic structures widespread in westernmost Nevada and the Sierra Nevada. If DI is a Sierra Nevada deformation event, then Luning-Fencemaker thrusting must postdate Middle-Late Jurassic deformation in the Sierra Nevada