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Insights into the Magmatic Plumbing System of Pavlof Volcano, Alaska through Volatiles in Olivine-Hosted Melt Inclusions

Valerie K. Wasser 1, Taryn M. Lopez 1, Jessica F. Larsen 1, Pavel E. Izbekov 1, Matthew Loewen 2, Christopher Waythomas 2, Megan E. Newcombe 3, Kayla Iacovino 4

  • Affiliations: 1 University of Alaska Fairbanks, Geophysical Institute, Alaska Volcano Observatory, Fairbanks,  Alaska; 2 USGS Alaska Volcano Observatory, Anchorage, Alaska; 3 University of Maryland, College Park, Maryland; 4Jacobs--NASA Johnson Space Center, Houston, Texas 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 227

  • Programme No: 1.1.13

  • Theme 1 > Session 1

Abstract

Pavlof Volcano, Alaska, USA, is a frequently active, basaltic-andesite stratovolcano that typically erupts with limited or no recognized precursory signals. Previous studies have found little evidence to support the presence of a persistent shallow magma reservoir, but barometry studies have been limited. Here we investigate Pavlof Volcano's magma system using volatile concentrations in olivine-hosted melt inclusions from two prehistoric eruptions. Results from Fourier-transform infrared spectroscopy and electron microprobe analyses find that inclusions contain <0.5 to >5 wt% H2O (N=61), 400--2,800 ppm S (N=14), <30 ppm (~detection limit) to 700 ppm CO2 (N=61), and Fo=70--75 in the host olivine. CO2 in shrinkage bubbles of inclusions is accounted for with thermodynamic modeling in MIMiC. Analyses of sulfur Kα peak shifts suggest the system fO2 is ~NNO+0.5. H2O and CO2 volatile saturation pressures calculated with the MagmaSat model indicate equilibrium pressures ranging from <100 bar (<0.5 km) to 2500 bar (9 km). Degassing models show that no single degassing path from one initial volatile concentration can explain all the data. A possible explanation for the wide range of H2O concentrations and saturation pressures is that some magma stalled at a depth of several kilometers and experienced diffusive H2O-loss. Furthermore, while most CO2-rich melt inclusions follow closed-system degassing paths, a second population of inclusions with low CO2 is more consistent with open-system degassing paths and shallow entrapment, potentially indicating variability in degassing processes.  This study aims to provide new constraints on Pavlof's magma plumbing system to help inform future volcano monitoring efforts.