Microlite textures and volatile contents of obsidian from the Inyo volcanic chain, California

We test the hypothesis that microlite textures record progressive degassing during magma ascent. We compare microlite number density (N-V) and H2O concentrations in pyroclastic and effusive obsidian (OBS) from the Inyo Volcanic Chain, CA. Comparisons reveal a weak correlation between microlite N-V and H2O; however, most obsidians (OBSs) of a given volatile content exhibit a wide range of N-V. Factors other than degassing must also influence final groundmass texture. We postulate that OBS textures record different ascent rates and residence histories prior to eruption from the conduit. We conclude that microlites do not sensitively indicate the extent of magmatic degassing, rather, they provide qualitative indications of magma ascent and residence time.