Congratulations to Yi Yu who successfully defended his dissertation on April 27, 2016.
Advisor: Youxue Zhang
Mineral dissolution and growth in magmatic melts are basic processes for understanding more complex geological processes such as magma crystallization and assimilation, xenolith and phenocryst digestion, lunar crust formation and etc. A good understanding of the kinetics of mineral dissolution and growth can shed light on further quantitatively modeling these processes.
This dissertation aims to study the dissolution kinetics of anorthite and quartz – two major minerals in the lunar crust and Earth’s continental crust, respectively, with a goal to model the diffusive dissolution of these minerals in magmatic melts, and further account for large-scale magmatic processes, such as lunar anorthosite crust formation. The first experimental study focused on anorthite dissolution in a basaltic melt at 1280-1500 °C and 0.5 GPa on two different crystallographic surfaces. As the equilibrium-dominant component of anorthite in the basaltic melt, the diffusion of Al2O3 largely controls the dissolution of anorthite. By incorporating the literature data on anorthite-melt equilibrium and Al2O3 diffusivities, a diffusive dissolution model of anorthite was set up, and further applied to model the convective dissolution of anorthite in the basaltic melt. This model could provide some preliminary insights into the formation of the lunar anorthosite crust. The second and third studies together investigated quartz dissolution in a rhyolitic melt and a basaltic melt at 1300-1600 °C and 0.5 GPa, respectively. As the only constituent of quartz, SiO2dictates the quartz-melt equilibrium and the mass transport in the melts. With a wide range of melt composition coverage, the diffusivity of SiO2 was shown to exponentially depend on XSi+Al, the cation mole fraction of Si+Al in the melt. Especially, the effect of H2O on SiO2 diffusivity is simply dilution of Si+Al in the melt. The compositional dependence was also quantified using functional fitting. With the reconciliation of SiO2 diffusivity across different melts, a diffusive dissolution model of quartz was built across rhyolitic, andesitic and basaltic melts..