|Keywords:||Ruapehu; phase equilibria; thermodynamics; rhyolite-melts; geobarometry; Taupo Volcanic Zone; ParanÃ¡; Brazil|
|Full text PDF:||http://etd.library.vanderbilt.edu/available/etd-07212016-204340/|
A new phase equilibria âmagma-meterâ determines a number of magmatic storage and crystallization conditions, including pressure, oxygen fugacity (fO2), state of fluid saturation, and maximum temperature for glass-bearing rocks containing the assemblage plagioclase+orthopyroxene+clinopyroxene (plag+opx+cpx). This newly developed magma-meter can better constrain crystallization conditions of shallow, glass-bearing andesites to dacites. The magma-meter utilizes rhyolite-MELTS to determine crystallization conditions utilizing the glass compositions coexisting with the plag+opx+cpx assemblage in natural samples. The magma-meter retrieves crystallization conditions for experiments from the literature. We applied the magma-meter to the plag+opx+cpx-bearing systems: Mt. Ruapehu, in the southern Taupo Volcanic Zone, New Zealand, and the Palmas unit of the ParanÃ¡ volcanic province, Brazil. The samples from Mt. Ruapehu and ParanÃ¡ were tested from ~5 MPa to ~400 MPa and from super-liquidus to ~90% crystalline (~1200 ÂºC to ~700 ÂºC). Mt. Ruapehu is an active, structurally well-understood volcano; it serves as a methodological testing ground for the magma-meter. Results show a distribution of crystallization pressures for different eruptions, with modes of ~110 MPa and 130 MPa, consistent with field interpretations of different eruptive styles based on juvenile clast textures and previous knowledge of the magma plumbing system. The distribution indicates that the magma batches were stored over a range of pressures. Mt. Ruapehu magmas are water saturated, with fO2 of ÎQFM ~+1. ParanÃ¡ includes extinct, super-eruption deposits, with preliminary results suggesting shallow (~90 MPa) storage conditions. Advisors/Committee Members: Guilherme Gualda (chair), Lily Claiborne (committee member).