Multiple episodes of Oligocene and younger silicic volcanism are represented in the high lava plateau of central and southeastern Oregon. From 12 Ma to Recent, volcanism is strongly bimodal with nearly equal volumes of basalt and rhyolite. It is characterized by moderate to high silica (SiO₂ > 72 wt. %)...
Understanding continental crust formation and modification is a fundamental and longstanding geologic problem. Influx of mantle-derived basaltic magma and partial melting of the crust are two ways to drive crustal differentiation. This process results in a low density upper crust and denser, more refractory lower crust, creating significant and vastly...