Abstract

We present new physical, geochemical, geochronologic, and oxygen isotope constraints on the mid-Miocene Jarbidge Rhyolite in northeastern Nevada (USA), providing new constraints on the tectonomagmatic evolution of the Cenozoic northern Great Basin. Widespread extension due to rapid collapse of the Nevadaplano began at ca. 17–16 Ma across the northern Great Basin. Coeval with this event was compositionally bimodal basalt-rhyolite volcanism that is often attributed to the inception of the Yellowstone hotspot. The most widespread mid-Miocene volcanic units in northeastern Nevada are lavas and domes of the Jarbidge Rhyolite. The thickest and most areally extensive exposures of these lavas include, and are found just west of, the Jarbidge Mountains, Nevada. This study focuses on Jarbidge Rhyolite directly south of the central Snake River Plain, adjacent to the thickest exposures in the vicinity of Jarbidge, Nevada. Textures on a range of scales indicate that the Jarbidge Rhyolite consists primarily of phenocryst-rich lavas. Laser 40Ar/39Ar ages for sanidine are consistent with effusive eruption of metaluminous to slightly peraluminous ferroan calc-alkalic rhyolite from 16.1 to 15.0 Ma; prior K-Ar ages suggest that some activity occurred over a slightly longer duration. Major and trace element data, coupled with new stable and prior radiogenic isotope measurements, suggest that Jarbidge Rhyolite magmas formed primarily via melting of quartzofeldspathic crust. The Jarbidge Rhyolite lavas are geochemically dissimilar from younger Snake River Plain rhyolites (e.g., lower MgO, lower Nb, higher Rb/Nb) and are more similar to coeval rhyolites erupted to the west on or adjacent to the Oregon Plateau. The distribution of the Jarbidge Rhyolite lavas in northeastern Nevada reflects an intimate association with temporally and spatially coincident extension rather than the Yellowstone hotspot.

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