CHEMICAL AND TEMPORAL CONSTRAINTS ON THE CENOZOIC VOLCANIC GEOLOGY OF THE LITTLE GOOSE CREEK AREA, NORTHEASTERN ELKO COUNTY, NV

The Little Goose Creek area is located in Elko County, Nevada just south of the central Snake River Plain and Cassia Mountains, in the northeastern Great Basin. During the Miocene, northeastern Nevada was characterized by volcanism as well as prevalent extension and basin development, including widespread occurrences of porphyritic quartz-phyric silicic lavas and domes (e.g., the Jarbidge Rhyolite), ignimbrites, and basaltic volcanism. Recent workers (e.g., Colgan and Henry, 2010) have provided new constraints on the timing of extension in the northern Great Basin (U.S.A.) and indicate that much of it occurred in the mid-Miocene. Other recent work has provided new temporal and petrologic constraints on 16.1 to 15.0 Ma Jarbidge Rhyolite volcanism in the northern Great Basin west of our study area, and suggest that it is intimately linked (spatially and temporally) with the aforementioned extension. This study aims to: [1] understand the spatiotemporal link between the volcanism in the northeastern Nevada study area and potentially correlative volcanism regionally (e.g., Jarbidge Rhyolite and explosive deposits associated with the <13 Ma Bruneau-Jarbidge or Twin Falls eruptive centers); [2] determine if the sampled Jarbidge Rhyolite lavas are chemically similar to those in and around Jarbidge, Nevada. We report a new laser ⁴⁰Ar/³⁹Ar age for sanidine of 13.6 ± 0.03 Ma from a crystal-poor rhyolite lava (Rock Springs Rhyolite); new ages on local Jarbidge Rhyolite lavas are pending. These lava samples, as well as sampled ignimbrites from the surrounding region (including in the Goose Creek drainage), plot within the A-type field on discrimination diagrams. The ignimbrites are younger than the Rock Springs Rhyolite based on stratigraphic relationships and likely sourced from the Twin Falls eruptive center of the central Snake River Plain. Also, a sequence of basaltic lavas crop out in the Little Goose Creek-Goose Creek drainages; these basalts have ~44 wt.% SiO₂ and are chemically similar to <8 Ma basalts that crop out to the north, along the southwestern side of the Cassia Mountains, Idaho. These results, field relationships, and prior geological mapping suggest that the lavas and ignimbrites erupted into active extensional basins.