| This thesis focuses on the nature of hydrous magmatism found in subduction zone settings. A unique perspective of this complex process has been gained through fieldwork as well as high pressure and temperature experiments. The first chapter gives the tectonic setting and geologic history for the subduction-related continental volcanic arc found in Western Mexico. It also describes mafic volcanic units that do not carry the expected subduction-related chemical signature, and that give insight into the complexity of the melting processes occuring beneath the arc. The remaining three chapters are devoted to experimental studies on how water affects the chemical behavior of magmas from subduction zone settings.; The second chapter investigates the potential effect of water on the redox state of iron in natural silicate melts. The result of this study is that there is no discernible effect of water on the redox ratio of iron. This is important in that it allows the use of established anhydrous empirical models to predict the ferric-ferrous ratios of hydrous silicate liquids, and is a necessary first step in investigating the effect of hydrous minerals on the redox state of magmas.; Knowledge of water solubility in magmas as a function of composition, temperature, and pressure, is fundamental to our understanding of subduction zone magmatism. Chapter three contains the results of new experiments that, along with data from the literature, allowed the development of a simple, empirical model of water solubility for a range of natural compositions and pressure and temperature.; The final chapter reports the results of hydrous phase equilibria studies on two subduction-related lavas. These two different compositions manifest themselves as lavas with differing phase assemblages that are known to be related to the pre-eruptive water content of their magmas. With these results, along with the water solubility model developed in chapter three, the water content necessary for each assemblage can be quantified, and results on how water affects the olivine/liquid equilibria for magmas is given. |
