The association of Hawaiian-Emperor volcanism with a large-scale central Pacific anisotropy anomaly at ~150 km depth can be explained by tapping of shallow melt sources in a perisphere/LLAMA (layer of lateral advection of mass and anisotropy) model. The origin of the anisotropy anomaly can be traced to the formation of a phlogopite-garnet-pyroxenite assemblage in the perisphere beneath an island arc on the Stikine terrane of the North American Cordillera in the Carboniferous. The pyroxenites were formed when subduction-related melts invaded the mantle wedge at ~150–200 km depth. The enriched region inherited the thermal profile of the mantle wedge, along with a solar-like noble gas isotopic composition from earlier fluxing of hydrothermal fluids between interplanetary dust particle–bearing deep-sea sediments and ultramafic layers of the oceanic crust prior to subduction. After termination of subduction, the enriched perisphere was displaced to the northeast beneath the Farallon plate, and then to the northwest beneath the Izanagi and Pacific plates, eventually becoming distorted into the shape of the present-day central Pacific anisotropy anomaly. During the thermal equilibration time, estimated at ~170 m.y., the phlogopite-garnet-pyroxenite assemblage followed a horizontal trajectory in pressure-temperature ( P-T ) space. As the P-T path crossed the solidi for volatile-bearing pyroxenite compositions, diabatic partial melting generated carbonatitic to alkaline melts which began to ascend and metasomatize shallower levels of the perisphere, carrying with them the geochemical signature of the original pyroxenites. The present central Pacific anisotropy anomaly is the current manifestation of the metasomatized domain. The latter was tapped from the Late Cretaceous to the present, by propagating fractures induced by large-scale plate reorganizations in the northwest of the Pacific Basin, to produce the Hawaiian-Emperor volcanic chain.

Continental flood basalt provinces are the subaerial expression of large igneous province volcanism. The emplacement of a continental flood basalt is an exceptional volcanic event in the geological history of our planet with the potential to directly impact Earth's atmosphere and environment. Large igneous province volcanism appears to have occurred episodically every 10–30 m.y. through most of Earth history. Most continental flood basalt provinces appear to have formed within 1–3 m.y., and within this period, one or more pulses of great magma production and lava eruption took place. These pulses may have lasted from 1 m.y. to as little as a few hundred thousand years. Within these pulses, tens to hundreds of volumetrically large eruptions took place, each producing 10 3 –10 4 km 3 of predominantly p3hoehoe lava and releasing unprecedented amounts of volcanic gases and ash into the atmosphere. The majority of magmatic gas species released had the potential to alter climate and/or atmospheric composition, in particular during violent explosive phases at the eruptive vents when volcanic gases were lofted into the stratosphere. Aside from the direct release of magmatic gases, magma-sediment interactions featured in some continental flood basalt provinces could have released additional carbon, sulfur, and halogen-bearing species into the atmosphere. Despite their potential importance, given the different nature of the country rock associated with each continental flood basalt province, it is difficult to make generalizations about these emissions from one province to another. The coincidence of continental flood basalt volcanism with periods of major biotic change is well substantiated, but the actual mechanisms by which the volcanic gases might have perturbed the environment to this extent are currently not well understood, and have been little studied by means of atmospheric modeling. We summarize current, albeit rudimentary, knowledge of continental flood basalt eruption source and emplacement characteristics to define a set of eruption source parameters in terms of magmatic gases that could be used as inputs for Earth system modeling studies. We identify our limited knowledge of the number and length of non-eruptive phases (hiatuses) during continental flood basalt volcanism as a key unknown parameter critical for better constraining the severity and duration of any potential environmental effects caused by continental flood basalt eruptions.

Abstract The northwest rift zone (NWRZ) eruption took place at Newberry Volcano ~7000 years ago after the volcano was mantled by tephra from the catastrophic eruption that destroyed Mount Mazama and produced the Crater Lake caldera. The NWRZ eruption produced multiple lava flows from a variety of vents including cinder cones, spatter vents, and fissures, possibly in more than one episode. Eruptive behaviors ranged from energetic Strombolian, which produced significant tephra plumes, to low-energy Hawaiian-style. This paper summarizes and in part reinterprets what is known about the eruption and presents information from new and ongoing studies. Total distance spanned by the eruption is 32 km north-south. The northernmost flow of the NWRZ blocked the Deschutes River upstream from the city of Bend, Oregon, and changed the course of the river. Renewed mafic activity in the region, particularly eruptions such as the NWRZ with tephra plumes and multiple lava flows from many vents, would have significant impacts for the residents of Bend and other central Oregon communities.