Oxygen and Hydrogen Isotope Studies of Igneous Rocks and Associated Hydrothermal Alteration

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9317036 Taylor Low-18O hotspots like Hawaii may represent recycled low-18O oceanic crust. This hypothesis will be tested by 18O/16O mapping of volcanic rocks associated with mantle plumes, initially focusing on the Samoa and Guadalupe hotspot chains. A laser fluorination apparatus is being constructed, allowing the analysis of 18O/16O on very small samples; it will be used to study detailed 18O/16O exchange behavior of aqueous fluids and coexisting minerals and volcanic glasses. Two other on-going projects will be completed: (1) Hydrothermal Effects Associated with Chegem Caldera, Caucasus Mtns., Russia. This is the most deeply erode, best exposed, young (2.8 Ma) caldera in the world; it contains a remarkable zone of 18O depletion in a 700 m- thick section of caldera-fill ash-flow tuff, where coexisting phenocrysts and volcanic glass are drastically out of 18O/16O equilibrium. (2) Hydrothermal Systems Associated with Faulting in Metamorphic Core Complexes, British Columbia. This isotopic study of some of the largest metamorphic core complexes in the world will provide new insight into the permeabilities of major fracture zones in the earth's crust, and may help us to understand the role of aqueous fluids in earthquakes.