Macquarie Ridge Complex basalt isotope geochemical data

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Strontium, Nd and Pb isotopic data of basalt samples from the Macquarie Ridge Complex (MRC).

The MRC samples include basalts collected from Macquarie Island, the only exposed portion of the submarine Macquarie Ridge, by R. Merle and K. Evans during a field trip in November 2017, and dredge samples collected by the National Institute of Water and Atmospheric Research, New Zealand, during the TAN0803 voyage in 2008.

Analytical methods of the isotopes: samples were first crushed and pulverized into powders using a zirconia vessel at Genalysis Laboratory Services, Perth. Sample chemistry and radiogenic isotope ratios of Sr (87Sr/86Sr), Nd (143Nd/144Nd) and Pb (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb) measurements by mass spectrometry were measured at the University of Geneva, Switzerland. The whole rock powders were dissolved in Savillex® Teflon vials using HF and HNO3 in ultrasonic bath for 30 minutes twice a day at 140°C, and then dried and re-dissolved in HNO3 for 3 days and dried again. Purification and elution of Sr, Nd and Pb were performed using cascade columns with Sr-Spec, TRU-Spec and Ln-Spec resins. The materials were then re-dissolved in a 2% HNO3 solution and ratios were measured using a Thermo Neptune PLUS Multi-Collector ICP–MS in static mode. Ratios used to monitor internal fractionation were as follows: 88Sr/86Sr = 8.375209 for the 87Sr/86Sr ratio, 146Nd/144Nd = 0.7219 for the 143Nd/144Nd ratio, and 203Tl/205Tl = 0.418922 for the three Pb ratios (a Tl standard was added to the solution). External standards were used to monitor the long-term external reproducibility: SRM987 (87Sr/86Sr = 0.710248: McArthur et al., 2001; long-term external reproducibility: 10 ppm, 1σ), JNdi-1 (143Nd/144Nd = 0.512115; long-term external reproducibility: 10 ppm, 1σ), and SRM981 for Pb (long-term 1σ external reproducibility: 0.0048% for 206Pb/204Pb, 0.0049% for 207Pb/204Pb and 0.0062% for 208Pb/204Pb). Due to a systematic difference between measured and accepted standard ratios, 87Sr/86Sr, 143Nd/144Nd and Pb isotope ratios were corrected for external fractionation by a value of -0.021‰, +0.051‰ and +0.36‰ a.m.u., respectively. Interferences at masses 84 (84Kr), 86 (86Kr) and 87 (87Rb) were corrected by monitoring 83Kr and 85Rb, the 144Sm interference on 144Nd was monitored on the mass 147Sm and corrected using a 144Sm/147Sm value of 0.206700 and the 204Hg interference on 204Pb was corrected by monitoring 202Hg. Total procedural blanks were <500 pg for Pb and <100 pg for Sr and Nd; these values are insignificant compared to the amounts of these elements measured in the investigated samples.

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Purpose
The Sr, Nd and Pb isotopic data of basalts from the Macquarie Ridge Complex (MRC) are used to study the mantle source of the MRC area.