Detrital zircon geochronology of Upper Triassic strata in western Nevada

Several distinct assemblages of basinal, volcanic arc, and shelfal strata in western Nevada are separated from each other and from adjacent assemblages by known and inferred thrust and strike-slip faults. We analyzed 84 detrital zircon grains from Upper Triassic strata in three assemblages to constrain their paleogeography and tectonic history. Basinal strata that probably belong to the Lovelock assemblage yielded grains with ages between 950-11 40 Ma, three grains of ca. 1417 Ma, and grains with a scattering of ages between 227 and 683 Ma. Shelfal strata of the Luning assemblage yield grains with ages mainly of 218-229 and 1643-1966 Ma; additional grains have ages of ca. 272, 1058, 1089, 1438, 1444, and 2325 Ma. All grains analyzed from the volcanic-rich Pine Nut assemblage yielded ages of ca. 231 Ma. The detrital zircon grains were apparently derived from sources both to the east and the west. The 1.40-1 .45 and 1.63-1 .74 Ga grains most likely originated in Precambrian basement of the southwestern United States, which contains igneous rocks of these ages. Grains >1.8 Ga could have been derived from the Golconda or Roberts Mountains allochthons to the east, or the northern Sierra and eastern Klamath terranes to the west. Grains of Paleozoic and Triassic age probably originated in preexisting and active magmatic arcs to the west. These provenance ties are consistent with stratigraphic and regional tectonic arguments suggesting that Triassic assemblages in western Nevada formed in a backarc basin between the Sierra-Klamath arc terranes to the west and the Cordilleran continental margin to the east.