Integrated geochemical modeling of magmatic degassing and hydrothermal interaction at Kaway Ijen volcano, Indonesia

Poster presentation at the <a href="http://www.iugg.org/">International Union of Geodesy and Geophysics (IUGG)</a> conference, Montreal, Canada (July 8-18, 2019). <p>Monitoring active volcanoes requires an understanding of magmatic degassing in relation to magma depth, temperature, composition, style of degassing (open vs closed) and interactions with hydrothermal systems. This conference presentation combines results of subsurface degassing (interpreted from melt inclusions) with measurements of fumarole gases and acid spring waters from Kawah Ijen volcano, Indonesia. Kawah Ijen is a stratovolcano with a growing rhyolite dome on the shore of a hyperacidic crater lake. The dome is emitting sulfur-rich gases from high temperature fumaroles (350-450°C). Matrix glass and melt inclusion compositions (including H2O, CO2, S, Cl and F) were measured for basaltic, dacitic and rhyolitic magmas. The behavior of the volatile species (Dvap-melt) during ascent, degassing and crystallization were modeled for an open system (including vapor fluxing) assuming Rayleigh fractionation, and for closed system processes assuming batch degassing and crystallization. The variable H2O-CO2 contents of the melt inclusions suggest that open system vapor fluxing (XH2Ovapor = 0.25-0.95 for basalt; 0.9-0.95 for dacite) is the dominant degassing style. The modeled S Dvap-melt values for basalt remain low (2-10) as the melt ascends (P= 400 to 100 MPa), then increase sharply to 200 at pressures.</p>