MAGMA CHAMBER TO THE OCEAN SURFACE: WHAT WATER TELLS US ABOUT PRE- AND SYN-ERUPTIVE SUBMARINE VOLCANIC PROCESSES
Melt inclusions contain 5 – 7 wt % H2OT and < 300 ppm CO2 suggesting deep storage conditions at 150-250 MPa of a very hydrous silicic melt which subsequently underwent closed-system degassing during ascent. Undersaturated residual OH contents in matrix glass, relative to the 650 – 900 m vent depth, imply either: 1) much shallower quenching pressures in the water column from slower cooling rates, or 2) the presence of coupled-volatile solubility conditions during magma ascent. Presence of excess H2Om in the matrix glass show that Havre products have been rehydrated post-degassing, but on rapid timescales inconsistent with our current understanding of water diffusion in the marine setting. Micro-Raman measurements spatially resolve this rehydration as mostly limited to bubble rims rather than throughout the glass. This suggests a novel syn-eruptive rehydration mechanism that may be unique to the deep-submarine volcanic setting, which we here explore.