Collaborative Research: Bubble Trouble - Re-evaluating olivine melt inclusion barometry and trace-element geochemistry in the Cascades

About This Grant

Determining the depths at which molten rock (magma) is stored and processed in the crust is vital for interpretations of volcanic unrest in the lead up to eruptions and for understanding of the chemical evolution of the Earth’s continents. Despite their importance, the structure and operation of the regions which supply magma to the surface remain poorly understood. It is currently uncertain, for example, whether magma is distributed across “mush zones” spanning the entire crust or stored in distinct “magma chambers”. This project will re-evaluate magma storage depths and the origin of chemical variability in volcanic systems in the Cascades using an approach that makes use of small pockets of magma trapped within erupted crystals, termed melt inclusions. Crucially, the CO2 contents of small bubbles within these melt inclusions will be measured directly, in addition to the surrounding melt. This project will contribute to the scientific understanding of volcanism along the Cascade arc, which presents a significant hazard to society. It will also foster close collaborations and a multi-tiered, peer-to-peer mentoring structure between two early career PIs, two graduate students, and multiple undergraduate students. The grant will also support a mentoring program for scientists with disabilities and a virtual forum for academics with chronic illnesses and invisible disabilities to share their stories about adapting to fieldwork, conferences, and workshops. The volatile contents of olivine-hosted melt inclusions provide important constraints on the depths at which mafic magmas erupting in the Cascades were stored and staged prior to eruption. However, the vast majority (97%, N=410) of previously published olivine-hosted melt inclusion data from the Cascades did not measure CO2 in vapor bubble(s). Preliminary Raman analyses of N=339 Cascade vapor bubbles indicates that without these measurements, storage depths have been underestimated by factors of 2-5X. Measuring melt inclusion volatile contents while accounting for CO2 and carbonate in the vapor bubble (using in situ heating experiments) will better constrain magma storage depths in different regions of the Cascades and provide insights into any variations in storage depth along strike (perhaps due to melt H2O contents, crustal stress state, or magma flux rate). While whole-rock trace element analyses are commonly used to assess magmatic processes in both the crust and mantle, whole-rock samples are generally an amalgamation of materials assembled and modified over a great range of unknown depths. Trace element measurements from melt inclusions with known entrapment depths will better constrain assimilation and mixing processes affecting liquid compositions and can reveal where in the crust these processes occur. He isotope data from aliquots of olivine from the same samples will further constrain the extent to which crustal materials have contributed to the most mafic components. Together, these data will provide unique insights into the origins of enriched signatured of continental arc magmas. This study will also assess mantle melting conditions, the processes causing mafic magmas to stall in the crust, and other topics relevant for melt inclusion studies worldwide (e.g., identifying processes forming carbonate in vapor bubbles and testing bubble growth models). Graduate and undergraduate students will acquire skills in a wide variety of hands-on geochemical techniques, data interpretation, coding, and software development. Students will build networks by travelling to different laboratories, interacting with collaborators at academic and government institutions, and presenting their findings at professional conferences. The grant will also support the development and improvement of open-source software tools, helping the volcanological community move to data processing and modelling workflows which are findable, accessible, interoperable, and reusable (FAIR). The PIs will also co-ordinate a virtual forum with panelists and a Q&A to share the voices and experiences of individuals with invisible disabilities with a broader audience, with a focus on laboratory and field work. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.