U-Pb detrital zircon geochronology of the Golconda allochthon, Nevada

The Golconda allochthon consists of deformed and imbricated deep-marine strata and volcanic rocks of late Paleozoic age that structurally overlie lower Paleozoic rocks of the Roberts Mountains allochthon and overlying upper Paleozoic strata. We analyzed 86 detrital zircon grains from 4 sandstone units of the Golconda allochthon in an effort to help reconstruct the paleogeographic and tectonic setting of the allochthon prior to Permian(?)-Triassic thrusting onto the continental margin. Of these, 81 grains yielded concordant to moderately discordant ages that define three main groups: 338-358 Ma (n = 7), 1770-1922 Ma (n = 38), and 2474-2729 Ma (n = 19). Comparison of these ages with detrital zircon age spectra from adjacent terranes indicates that most of the detritus in Golconda sandstones was probably shed from rocks of both the Roberts Mountains allochthon to the east and the northern Sierra terrane to the west. Some grains may also have been shed from basement rocks of the southwestern United States. These relations support previously proposed tectonic models in which strata in the Golconda allochthon were deposited between the Sierra-Klamath magmatic arc to the west and the previously emplaced Roberts Mountains allochthon to the east.