Abstract

The northern Pilot Mountains of west-central Nevada consist of a complexly deformed terrane of imbricate thrust sheets composed of rocks of Mesozoic and possible late Paleozoic ages. Thrust nappes within the allochthonous terrane, named the Luning allochthon, are principally constituted by the Upper Triassic Luning Formation. Locally, the nappes contain numerous imbricate thrust slices, some of which are composed of undifferentiated Sunrise-Gabbs Formation (Triassic and Jurassic) and unnamed volcanic-carbonate assemblages of probable Permian or Triassic age.

Three episodes of folding and thrusting are recognized on the basis of folded thrusts and thrusted folds, and deformation and emplacement of the allochthon is constrained as late Mesozoic. Folds apparently formed coevally with thrust faults and fold geometry is used to determine approximate directions of thrust transport. Thrust displacements are responsible for 35 to 40 km of an estimated 70 km of intra-allochthon contraction which is inferred from lithofacies analysis of rocks juxtaposed by thrust nappes and from the structural overlap of imbricate thrusts.

The history of thrust displacement is complex and involves three directions of motion on a regionally extensive detachment surface, the Luning thrust. First motion, from northwest to southeast, resulted in the major component of stratal contraction and is the probable result of northwest-southeast regional compression. The final two episodes of motion are northeast to southwest followed by east to west; they resulted in small displacements and are possibly the product of gravity sliding of the thrust sheets into a depression formed beneath part of the allochthon within the autochthon. The site of downwarp in the autochthon may have formed by either load-induced subsidence or regional compression.

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