Volatiles of the Cascadia Arc

Dan Ruscitto is studying mafic volcanism in the Central Oregon High Cascades. His reserarch focuses on pre-eruptive (i.e. initial) volatile contents trapped within olivine-hosted glass inclusions from eruptions producing the abundant cinder cones (and lava flows) located throughout the area. These eruptions are smaller, more frequent, and historically have been under-studied compared to their larger, catastrophic cousins (e.g. St. Helens, Pinatubo). Dan’s research can be separated into deep– (e.g. mantle–melting) and shallow–level (e.g. ascent and degassing) processes and he is investigating how these systems are related by integrating geochemical and physical volcanological techniques. Two separate but interrelated aspects of this study are: 1) investigating the role of volatiles and their recycling efficiencies in a hot and dry subduction zone environment and 2) understanding the relationships between magmatic volatile contents and eruptive activity.

The Cascades have historically been viewed as a dry, and therefore, weak volcanic arc in terms of volumetric output, eruption frequency, and explosivity. Preliminary data, however, suggest a relatively large range in water contents (H2O = most abundant volatile in volcanic systems) of up to ~ 4 % by weight – concentrations similar to those found in other, more active arcs around the world. One objective of this study is to characterize the range in initial volatile contents to better understand past activity and, therefore, expected future activity in a volcanic arc situated in a heavily populated, developed country.

This research will form the basis for future theoretical and experimental studies and may be applicable to future hazard assessments. This is the first study of the Cascades directly relating all major volatile contents (H2O, CO2, S, F, and Cl) with major and trace element chemistry and mineralogy to constrain conditions of magma formation and evolution, a topic of considerable interest to the academic geological community.