Abstract (0422278) - Sims Currently there are very few U-series data from slow-spread spreading ridges and such data are critical to better understanding the global systematics of 238U- 230Th disequilibria and other isotopic systems in mid-ocean ridge basalts. The goal of this research is to measure (and compile) Nd, Sr, Pb and Hf isotopic compositions and U-Th-Ra and U-Pa disequilibria in a suite of samples from the shallow, slow-spreading Kolbeinsey ridge and from the Tjorne Fracture Zone, north of Iceland. Samples to be analyzed have already been collected and have been previously characterized for major- and trace element compositions by others. It is anticipated that the combined U-series, major and trace-element and isotopic data will allow us to better understand melt generation and transport processes beneath the Kolbeinsey Ridge and other slow-spreading mid-ocean ridges, and to assess the extent to which U-series disequilibria (and other trace-element fractionations) are controlled by melting processes and/or source heterogeneities. Data from slow spreading ridges will be compared with those from the fast spreading East Pacific Rise and others mid-ocean ridge systems to evaluate: (1) whether U-Th disequilibria is correlated with axial depth as has been observed for deep and intermediate depth ridges; (2) if data from individual ridge segments show a relationship between axial spreading rate and their slope on Th isochron plots and, it so, does the relationship require mixing of enriched and depleted mantle sources; and (3) whether the Iceland Plume influence the Kolbeinsey Ridge Broader impacts of the proposed study are the support of a female PhD student, international collaboration with three overseas laboratories, collaboration between modelers and analytical geochemists, and improved measurement techniques and better-calibrated Th isotopic standards which are critical for many solid Earth and oceanographic applications that use 238U-230Th disequilibria data.
