Eruptive history of the rhyolitic Kane Springs Wash Volcanic Center, Nevada

Abstract

The 19×13 km Kane Springs Wash caldera formed 14 Ma ago following eruption of the three youngest members of the Kane Wash Tuff. Two older cooling units of the Kane Wash Tuff are dated 15.7±0.2 Ma and 14.7±0.2 Ma and apparently erupted from source areas west of the exposed caldera. Volcanic eruptions from the Kane Springs Wash center began about 14 Ma ago with extrusion of trachyte lavas now preserved north of the caldera. Member V1 of the Kane Wash Tuff overlies the trachytes and is zoned from rhyolite to trachyte. In contrast, overlying members V2 and V3 are slightly peralkaline rhyolites (comendite). Eruption of these tuffs 14.1±0.2 Ma ago initiated caldera collapse. Following collapse, trachyte lavas indistinguishable in age from the ash‐flow tuffs erupted within the caldera, forming a 5‐m‐diameter cumulodome whose interior portions crystallized to syenite. This magmatic resurgence formed an extrusive complex within the caldera rather than doming the cauldron block as in classic resurgent calderas. Metaluminous ferroedenite‐rhyolite lavas and associated ash‐flow tuffs then erupted in the “moat” surrounding the central trachyte/syenite complex. Pyroclastic deposits from the domes were covered by trachyandesite and basalt lava flows about 13.4 Ma ago. Biotiterhyolite domes dated 13.4±0.2 Ma continued to erupt in the northeastern moat and appear to be the last silicic eruptions from the Kane Springs Wash magma system. A 13.4 Ma metaluminous biotite‐rhyolite dome containing vapor‐phase topaz overlies the trachyandesite lavas and appears to be the youngest biotite‐rhyolite dome. These intracaldera units filled the moat, resulting in a caldera filled with its own eruptive products. Local basalt flows covered both intracaldera units and outflow sheets between 12.7 and 11.5 Ma ago, prior to Basin and Range faulting. The “dominant volume” of the system was trachytic, as trachyte lavas erupted both prior to and following caldera collapse, and trachyte inclusions occur as scoriaceous bombs at the top of member V2. Fractionation of this trachyte magma produced the slightly peralkaline rhyolitic magma that erupted as the Kane Wash Tuff. The shift from an anhydrous mineral assemblage in the tuffs to hydrous assemblages in the later intracaldera rhyolites shows that the system was cooling and was possibly more hydrous in its late stages. Petrographic characteristics of trachyandesite lavas erupted late in the history of the center suggest that they represent basaltic magmas contaminated with silicic material