For Sr and Nd isotopic composition, the measured ratios are given with the 2sigma m (2 sigma on the mean of the measurement), whereas for Pb, the 2 sigma precision is <0.l % for 2 0 6Pb/204Pb and 207Pb/204Pb and <0.15% for 2 08Pb/204Pb. Measured ratios are normalized to 86Sr/88Sr = 0.1194 for Sr isotopic ratios and to 146Nd/144Nd = 0.7219 for Nd isotopic ratios. For Pb, a mass-fractionation correction factor of 0.13% ± 0.04% per atomic mass unit was applied to all the isotopic ratios, on the basis of 72 analyses of the NBS 981 Pb standard. The "initial" ratios were calculated at 38 Ma for Site 756, 58 Ma for Site 757, and 88 Ma for Site 758 (Peirce, Weissel, et al., 1989, doi:10.2973/odp.proc.ir.121.1989; R. A. Duncan, pers. comm., 1990). "Initial" 87Sr/86Sr ratios were calculated for unleached samples on the basis of their XRF-measured Rb and Sr concentrations. Assuming a comparable 87Rb/86Sr range (0 to 0.467) in the acid-leached samples to that in the unleached samples, the corresponding maximum corrections for 38, 58, and 88 Ma are, respectively, 0.00025, 0.00038, and 0.00058 for the 87Sr/86Sr ratios, which is significant, but will not change the general interpretation of the origin of Ninetyeast Ridge. The correction factors are much smaller for Nd because of the longer half-life of 147Sm in comparison with 87Rb (1.531011 and 7.0410**10yr).