Explosively erupting volcanoes and megathrust earthquakes (Mw 8+ magnitude) occur at subduction zones and adjacent volcanic arcs. Volcanic eruptions are observed occurring close in time to megathrust earthquakes in the historical record from at least the 18th century CE to present in locations globally, including Japan in 1707 CE (Chesley...
During volcanic eruptions ascending magma undergoes decompression, resulting in a decrease of dissolved H2O. This creates unstable conditions for the hydrous mineral amphibole. As a result a reaction rim forms from anhydrous minerals such as pyroxene, plagioclase, and Fe-Ti oxides (Rutherford and Hill, 1993). There have been numerous studies done...
The Tam McArthur Rim is a volcanic center located within the Tumalo Volcanic Field (TVF), approximately 25 km west of Bend, OR. The rim comprises of shallowly dipping bedded sequences of intermediate and silicic flows with minor tephra interbedding capped by a rhyodacite dome. Glacial activity has exposed significant portions...
The origin of hornblendite and other mafic mineral-rich veins found in Cretaceous plutonic rocks from the Northern Cascades is currently not well known. This study seeks to investigate the possible relationship between host plutonic rocks and hornblendite and pyroxene-rich veins by comparing the chemical compositions and petrographic features between the...
The Early Oligocene Oregon Coast Range Intrusions (OCRI) consist of gabbroic rocks and lesser alkalic intrusive bodies that were emplaced in marine sedimentary units and volcanic sequences within a Tertiary Cascadia forearc basin. The alkalic intrusions include nepheline syenite, camptonite, and alkaline basalt. The gabbros occur as dikes and differentiated...
Volcanic and sedimentary deposits of the Mount Jefferson area (MJA) record a fourmillion-year history of arc-related volcanism related to the subduction of the Juan de Fuca plate beneath North America. 171 mapped stratigraphic units over an area of 150 km² reveal four periods of volcanic activity resulting in diverse composition...
The origin of hornblendite and other mafic mineral-rich veins found in Cretaceous plutonic rocks from the Northern Cascades is currently not well known. This study seeks to investigate the possible relationship between host plutonic rocks and hornblendite and pyroxene-rich veins by comparing the chemical compositions and petrographic features between the...
The sheeted complex of the ~92 Ma Tenpeak pluton, in the Northern Washington Cascades crystalline core, forms a <1.5-km wide zone with a moderate, NE-dip at the SW margin of the pluton. Sheeted magmatic complexes, such as the one in the Tenpeak pluton, are common in plutons and represent examples...
Silicic volcanism in the central Oregon Cascade range has decreased in both the size and frequency of eruptions from its initiation at ~40 Ma to present. The reasons for this reduction in silicic volcanism are poorly constrained. Studies of the petrogenesis of these magmas have the potential for addressing this...
Snow Peak is a voluminous shield volcano located ~50 km west of the axis of
the modern Cascade arc. A previously published K-Ar age estimate indicates that the
Snow Peak lavas are ~3 Ma. Subsequently, the preliminary research framework for
studying the Snow Peak lavas focused on constraining the petrogenesis...