Structural fabric of the Paleozoic Golconda Allochthon, Antler Peak Quadrangle, Nevada: Progressive Deformation of an Oceanic Sedimentary Assemblage

The Golconda allochthon in Nevada consists of structurally complex mid to late Paleozoic basinal sedimentary and volcanic rocks deformed under low temperature and pressure conditions and emplaced onto the North American shelf in the Permo-Triassic. Above the basal thrust in the Antler Peak area, the allochthon consists (in ascending structural order) of late Early to early Late Permian thick bedded chert (‘Pumpernickel subunit 1 ’); Pennsylvanian and Early Permian thin bedded chert, argillite and siltstone (‘Pumpernickel subunit 2’); Mississippian siliciclastic turbidites (‘Jory unit’) and undated chert and argillite of the ‘Trenton unit.’ Open to tight folds in subunit 1 trend north-south and are east-vergent. Folds in thinner bedded subunit 2 vary considerably in style. Fold axes in this unit are distributed within the mean axial plane (oriented N-S, 60°W) but exhibit a west-northwest trending data gap. Boudin axes measured in zones of highly disrupted layering (interpreted as zones of movement or shear) exhibit similar patterns without data gaps. These girdled distributions in part reflect rotation of these elements upon greater strain towards the east-west trending direction of tectonic transport or towards parallelism with the X axis of the strain ellipsoid. Asymmetry of folds indicate movement was west to east. Locally developed late stage folds in subunit 2 are subhorizontal, trend north-south, and are compatible with fold-fault solutions that indicate east-directed thrusting. Striations measured within fault zones yield bidirectional east-west slip lines. Our fold and fault data indicate that east-west shortening of these basinal sediments was accomplished by folding and east-directed thrust faulting during a single progressive deformational event. This conclusion is supported by the presence of a major west-dipping thrust fault in the map area that places Mississippian over Permian rocks. The allochthon formed as an east-vergent submarine fold and thrust belt that was subsequently thrust on the continental shelf. Autochthonous rocks beneath the Golconda thrust are virtually undeformed, suggesting that most of the structure in the allochthon formed prior to its ultimate emplacement.