URANIUM THORIUM ISOTOPES AND TRANSITION-METAL FLUXES IN 2 ORIENTED MANGANESE NODULES FROM THE CENTRAL INDIAN BASIN - IMPLICATIONS FOR NODULE TURNOVER

Transition metal fluxes to the top and bottom of two oriented manganese nodules (SS-657 and SK-176) were determined by combining radiochemical and geochemical analyses. Distinct differences in transition metal fluxes, 230Th contents, 230Th 232Th and Mn Fe ratios and silicate mineralogy in the top and bottom of nodule SS-657 suggest that since the time of inception of oxyhydroxide accretion (< 1 m.y. B.P.) it has been growing with a fixed orientation on the seafloor. In nodule SK-176, in contrast, nearly uniform accumulation rates, 230Thexc and 230Thexc 232Th extrapolated to surface activities, transition metal fluxes and increasing diagenetic influence outwards in the top and bottom are thought to be suggestive of rotation of the nodule several times over time intervals which are smaller than the time resolution involved in U-Th isotope dating techniques. © 1990.