Filling critical gaps in the space-time record of High Lava Plains and co-Columbia River Basalt Group rhyolite volcanism

Miocene rhyolitic volcanism of eastern Oregon, USA, can be divided into two main episodes. Mantle plume upwelling is thought to have generated Columbia River Basalt Group (CRBG) lavas and coeval >16.5−15 Ma silicic trending north−south from northeast Oregon northern Nevada. Rhyolite the 12−0 High Lava Plains province has been ascribed either buoyancy-driven westward spreading or slab rollback mantle convection spanning southeast Newberry Volcano west. The apparent ca. 15−12 eruptive hiatus suggests that rhyolites these provinces were a product separate processes, yet this gap was based on incomplete data. lack data ∼33 total ∼50 centers in area where overlap (117−119°W, 43−44°N) yields only tenuous relationships between provinces. We acquired 40Ar/39Ar ages for 29 previously unanalyzed rhyolite confirm existence episode concurrent with CRBG flood basalt volcanism. eruptions gradually initiated at 17.5 Ma, our new indicate peak intensity first occurred 16.3 14.4 Ma. refine 14.4−12.1 strong recommencement began Beatys Butte 12.05 find prominent fluxes activity after 12.1 as opposed one continuous, age-progressive trend, 12.1−9.6 7.7−5.1 which are separated by an ∼2 m.y. period decreased scarce 5.1 point most associated Volcano. Periodicity along demands more punctuated inputs than what continuous partial melting west-spreading material should generate. Our suggest regional series episodic events related arrival storage mafic magmas. Paucity flux magmas 15 Strong continued Northwest Basin Range extension rotation rate Siletzia affecting lithosphere weakened Waning 9.6 7.7 reflects transition primary mode accommodation normal faulting shearing Brothers Fault Zone. driven less affected magmatism. Post-5.1 within crust not influenced magmatism but impacted both Cascadia subduction zone.