U-series and radiogenic isotope compositions of young anhydrite and sulfide minerals from seafloor hydrothermal deposits

Radioactive isotopes from the 238U- and 232Th-decay series and radiogenic isotopes of Pb, Nd and Sr were measured in eleven subsamples of known, zero-age anhydrite-rich chimneys, four subsamples of actively venting chimneys of unknown full age (likely less than a few years), and eight subsamples from “massive anhydrite” samples of unknown age. The materials analyzed were recovered from hydrothermal areas representing a variety of tectonic and geologic settings: the TAG active hydrothermal mound on the Mid-Atlantic Ridge, the “busted mushroom” structure in the southern trough of Guaymas Basin, four different vent fields along the eastern Lau Spreading Center/Valu Fa Ridge (ELSC/VFR) in Lau Basin, and the Fenway mound of PACManus. (230Th/234U), (226Ra/230Th), (210Pb/226Ra), (228Ra/232Th) and (228Th/228Ra) were measured from the 238U- and 232Th-decay series by MC-ICP-MS and Gamma spectrometry. 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 143Nd/144Nd, and 87Sr/86Sr were measured by MC-ICP-MS. Isotopes were measured to investigate the reliability of ages calculated using 238U- and 232Th-decay series nuclides in seafloor hydrothermal deposits.