Magmatic Environments and Timescales: Experimental Studies on Martian Basalt and Terrestrial Dacite

Abstract

Magmatic minerals and melts record the environmental conditions at which they equilibrate (fully or partially), via compositional and textural patterns related to time and the temperature, pressure, composition, and oxidation state of the magma. The quantification of these patterns can yield geothermometers, geobarometers, oxybarometers, and geospeedometers. These powerful petrological tools are paramount to interpreting the magmatic processes that occur in sub-volcanic plumbing systems over the life of a volcano, including shortly before eruptions, but they require extensive experimental calibration. This dissertation consists of four studies that determine system-specific indicators of magmatic processes, furthering experimental contributions to volcanology. First, experimental pyroxene textures are used as geospeedometers to derive cooling rates of the Yamato 980459 meteorite, which are consistent with eruption as a pāhoehoe flow on Mars. Second, phase equilibrium experiments on dacite from Volcán Quizapu, Chile reveal identical, tightly constrained, water-saturated storage conditions before both the 1846-7 effusive eruption and the 1932 Plinian eruption. Third, these same experiments are used to document the re-equilibration of hemoilmenite and titanomagnetite in natural melt, revealing that these minerals may not record magmatic temperature and oxygen fugacity as faithfully as previously thought. Fourth, a long-duration diffusion experiment shows that the diffusivity of Mg in labradorite is anisotropic and up to ~100 times faster than published values, likely due to the use of a natural, hydrous melt. Overall, the work herein highlights the importance of using complex, natural systems as the basis for experimental studies, to derive the most accurate quantifications of volcanic processes. The four studies presented demonstrate that the marriage of micro-scale textural and compositional parameters is a powerful means of elucidating the macro-scale magmatic history of volcanic systems.