Tectonic Erratics-Remarkable Exotic Blocks Emplaced by the Henderson Thrust During the Sonoma Orogeny, Eureka County, Nevada

摘要

Throughout north-central Nevada, Cambrian-Devonian siliciclastic strata of the Roberts Mountains allochthon (RMA), which was emplaced along the Roberts Mountains thrust during the Late Devonian-Early Mississippian Antler orogeny, overlie an autochthon of coeval largely carbonate strata. In Eureka County, masses of the carbonate strata also form topographic highs above the RMA, and on the east side of the Roberts Mountains they occur along a thrust fault, here termed the Henderson thrust, that duplicates the RMA and is constrained to the Permian-Late Jurassic. We propose that the Henderson thrust initially developed along the Roberts Mountains thrust and then ramped upward and eastward duplicating the RMA. In the process, carbonate blocks were plucked from the lower plate of the Roberts Mountains thrust and were incorporated and transported in the upper plate of the Henderson thrust. Following preferential erosion across substantial areas of the rocks of the RMA in the upper plate, carbonate masses were left in several places stranded on top of the strata of the RMA in the lower plate of the Henderson thrust. These exotic carbonate blocks are numerous, widespread, and often large. They are similar to glacial erratics in that they remain stranded on rocks of very different character-the rocks of the RMA in the lower plate of the Henderson thrust. The Henderson thrust is a structural expression of the deformation of the RMA during the Sonoma orogeny when the Golconda allochthon was emplaced against the RMA. The widespread occurrence of erratics at the surface and in the subsurface has important implications for petroleum and gold exploration in north-central Nevada.