Th Isotope and U-Series Disequilibria Studies by mass and Alpha Spectrometry

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It is now know that 238U-230th and 230Th-226Ra disequilibria in recent volcanics can be large, can differ in kind and extent according to tectonic environment, and can appear complex between coexisting minerals in zero-age rocks. It is also known that Th isotope ratios vary by more than most other isotope ratios, yet can be measured by Mass Spectrometer to 1%, or to within 1/1000 of the observed range. There also is potential to measure other short-lived nuclides, such as 226Ra and 231Pa mass spectrometrically as well. This will be a focused effort to explore the potential of high resolution, small-sample studies of U-Th-series systematics in young volcanic rocks. In particular it is planned to pursue four kinds of research over the next three years: 1) continued regional-scale study of subduction zones, in connection with two other monitors of slab recycling processes and timescales, Be and B; 2) continued study of submarine tholeiitic basalts from backarc basins; 3) continued study of magma chamber processes for magmas ranging in viscosity from carbonatite to rhyolite; and 4) continued study of global correlations of Th-Sr-Nd-Pb isotope ratios.