CO2 CONTENTS AND FORMATION PRESSURES OF SOME KILAUEAN MELT INCLUSIONS

Of 50 analyzed glass inclusions in Olivine phenocrysts from the 1959 K ilauea Iki eruption, 41 formed at pressures < 1 kbar, seven between 1 and 2 kbar, and two at pressures >2 kbar. The surprisingly low formati on pressures suggest that most 1959 olivines, including most of those with preeruptive equilibration temperatures above 1200-degrees-C, crys tallized in an upper part of Kilauea's summit magma storage reservoir. The implication that the parental magma was buoyant relative to store d magma is consistent with an expected preeruptive bulk CO2 content ne ar 0.2 wt% and published evidence for mixing between hot, newly arrive d parental and preexisting magma. That the 1959 magma was rich not onl y in crystals but also in gas, as evidenced by its high lava fountains , suggests that the storage time in a shallow reservoir was too short for either crystals or gas to be lost. Therefore, the 1959 Kilauean ma gma probably is a near-parental magma that rose and formed a gas- and crystal-rich cap near the top of a shallow body of stored magma beneat h Kilauea's summit region. Whether newly arriving parental magma is bu oyant relative to stored magma depends mainly on pressure and magma ga s content. Consequently, it seems likely that the eruptive and degassi ng behavior of Kilauea is regulated in part by an interplay between th e CO2 content of parental magma and the pressure at which new magma in trudes stored, degassed magma.