Geochronological and Geochemical Investigation into Rhyolite Volcanism of the High Lava Plains and Columbia River Basalt Group Provinces of Eastern Oregon, USA

Abstract

Voluminous and widespread bimodal volcanism has significantly impacted the Pacific Northwest, USA, throughout the Miocene to present day. The two primary volcanic provinces of eastern Oregon include the Columbia River Basalt Group (CRBG) province and the High Lava Plains (HLP) trend. The magmatic and tectonic processes responsible for generating bimodal volcanism, and particularly rhyolites of the ~17-15 Ma CRBG and 12-0 Ma HLP provinces has recently been a popular topic of debate. Rhyolite volcanism of the HLP province has been ascribed to either buoyancy-driven westward plume spreading or to slab rollback and mantle convection spanning from southeast Oregon to Newberry volcano in the west. Numerous studies have focused on the mafic endmember of these bimodal provinces (e.g., Hooper et al., 2002; Camp et al., 2003; Cahoon et al., 2020), but until recently, few workers had investigated the rhyolite endmember. Rhyolites of bimodal systems can possess unique geochemical and petrologic signatures and can contain components of their associated mafic endmembers, thus providing workers with critical evidence necessary to understand pre-eruptive magma configurations, magma chamber evolution, and rhyolite petrogenesis.