Hydrothermal Alteration and Contact Metamorphism in the Reykjanes Geothermal System: Implications for Fluid-Rock Interactions at Mid-Oceanic Ridge Spreading Centers

Mid-ocean ridge hydrothermal systems exert a profound effect on global geochemical cycles, are the source of novel biological communities, economically important mineral deposits, and heat loss from the earth's interior. Submarine vents were first discovered in 1977, and since then dozens of vents have been sampled. Despite significant advances in locating and sampling these systems, and the significance of hydrothermal circulation to global geochemical cycles, fundamental uncertainties remain. In this PhD thesis we explore several aspects of hydrothermal water/rock interaction in subaerial geothermal system that is analogous in many ways to submarine systems. The first chapter provides an overview of the importance of hydrothermal circulation, and introduction to the Iceland Deep Drilling Program, and a brief description of the following dissertation chapters. Chapter two describes the petrology and mineral chemistry of alteration phases in the Reykjanes geothermal system, and provides evidence of the influence of Pleistocene glaciation on the evolution of the system. Chapter three provides evidence of very high temperature contact metamorphism within the geothermal system, and documents the novel occurrence of pyroxene hornfels facies granoblastic textures within an active geothermal system. Chapter four provides isotopic evidence of both meteoric and seawater dominated hydrothermal fluids using 87Sr/86Sr and delta 18O isotopic systems. The appendices provide detailed lithologic logs of the RN-17 cuttings and RN-17B core.