Radiogenic isotope data for rock samples collected offshore Heard and McDonald Islands

Radiogenic isotope data (Sr-Nd-Pb-Hf isotopes) were acquired for six rock samples from two sea knolls around McDonald Islands and one sea knoll and two submarine hummocks near Heard Island. The samples were dredged during the RV Investigator voyage IN2016_V01 and are curated at the University of Tasmania. Samples were prepared at the University of Tasmania and analysed at the University of Melbourne.The dataset includes three files: 1. The location and petrographic descriptions of the samples, 2. A summary file of the analytical results, and 3. The raw analytical results for Sr-Nd-Pb-Hf isotopes.Sample SelectionSamples selected for analysis are a subset of samples collected from each dredge. Following macroscopic examination of the samples, polished rock thin sections were made of the least altered rocks. Following examination under petrographic microscope, the least altered samples were selected for isotopic analysis.Sample PreparationInitial sample preparation was undertaken at the University of Tasmania. After weathered material was removed from the outer edge of the rock samples, rock pieces were hand crushed in a ceramic mortar and pestle. Rock chips (~5 mm chips, 5-10 g) were cleaned in a ultrasonic bath of de-ionised water for 30 minutes.Analytical techniqueSr-Nd-Pb-Hf isotopes were acquired using a Nu Plasma multi-collector ICP-MS at the University of Melbourne (Maas et al., 2005).Splits of agate-milled powders (100-140 mg) were leached with 6M HCl (100oC, 60 min) and digested at high pressure (HF, 160oC, 48 hrs; HCl, 160oC, 12 hrs). Pb was extracted on small columns of AG1-X8 (100-200) anion exchange, using the HBr-HCl technique. Hf, Nd, and Sr were extracted from the HBr eluate of the Pb column, using Eichrom LN-, TRU/LN, and Sr resin, respectively Münker et al., 2001; Pin et al., 2014). Total analytical blanks (~50 pg for Pb and Hf; ≤100 pg for Nd and Sr) are negligible compared to the amounts of Pb, Hf, Nd, and Sr processed.All isotopic analyses were carried out on a Nu Plasma multi-collector ICP-MS with sample introduction via a low-uptake Glass Expansion PFA nebuliser and a CETAC Aridus desolvator. Sensitivity in this set-up is in the range of 130-150 V/ppm Sr, Nd, Pb, or Hf. Instrumental mass bias in Nd, Sr, and Hf analyses was corrected by normalizing to 146Nd/144Nd = 0.7219, 86Sr/88Sr = 0.1194, and 179Hf/177Hf=0.7325, respectively, using the exponential law. 143Nd/144Nd, 87Sr/86Sr, and 176Hf/177Hf are reported relative to La Jolla Nd = 0.511860, SRM987 = 0.710230, and JMC475 = 0.282160. Results for USGS rock and other standards are consistent with TIMS and MC-ICP-MS reference values. Typical in-run precisions (2sd) are ±0.000010 (Nd), ±0.000016 (Sr), and ±0.000008 (Hf). External (2sd) precisions are ±0.000020, ±0.000040, and ±0.000015, respectively. Mass bias for Pb was corrected using the thallium-doping technique (Woodhead, 2002). This produces data with an external precision (2sd) of ±0.04-0.06% for 206Pb/204Pb and 207Pb/204Pb, and 0.07-0.09% for 208Pb/204Pb. ReferencesMaas, R., Kamenetsky, M. B., Sobolev, A. V., Kamenetsky, V. S., and Sobolev, N. V. (2005). Sr, Nd, and Pb isotope evidence for a mantle origin of alkali chlorides and carbonates in the Udachnaya kimberlite, Siberia. Geology, 33(7), 549-552. https://doi.org/10.1130/g21257.1 Münker, C., Weyer, S., Scherer, E., and Mezger, K. (2001). Separation of high field strength elements (Nb, Ta, Zr, Hf) and Lu from rock samples for MC-ICPMS measurements. Geochemistry, Geophysics, Geosystems, 2(12). https://doi.org/10.1029/2001gc000183Pin, C., Gannoun, A., and Dupont, A. (2014). Rapid, simultaneous separation of Sr, Pb, and Nd by extraction chromatography prior to isotope ratios determination by TIMS and MC-ICP-MS [10.1039/C4JA00169A]. Journal of Analytical Atomic Spectrometry, 29(10), 1858-1870. https://doi.org/10.1039/C4JA00169AWoodhead, J. D., Greenwood, P., Harmon, R. S., and Stoffers, P. (1993). Oxygen isotope evidence for recycled crust in the source of EM-type ocean island basalts. Nature, 362(6423), 809-813. https://doi.org/10.1038/362809a0