Whole rock geochemistry – trace elements - from selected basalts dredged from seamounts in the south Tasman Sea during RV Investigator voyage IN2018_V08

Solution ICP-MS trace elements analysis in CODES, School of Physical Sciences (Earth Sciences), University of Tasmania (modified after P.Robinson by E.Lounejeva, August 2017) Digestion100.00 plus or minus 0.05 mg of rock powder was dissolved in a mixture of inorganic acids (HF:H2SO4=3:3) at 180 degrees C in closed PTFE vessels in Digestion Acid System (DAS, PicoTrace). The mixture was then evaporated to dryness. Solid residuals were dissolved in HClO4, evaporated, re-dissolved in HNO3 and then diluted to 100.000 plus or minus 0.050 ml. The resulting final solution contained the completely dissolved sample diluted 1000 times in a weak acid (2v/v% HNO3), 10 μg/ml of a mixture of Rh, In and Re as internal standard and traces of HF added to stabilize Ta and Nb. Digestion reagents blanks and international standards were processed along samples. All the solutions were then analysed by inductively coupled plasma mass spectrometry (ICP-MS) on an Agilent-7700x instrument within 48 hours of dilution. Calibration of the instrument involved high purity standards solutions (CHOICE Analytical) for quantification and for estimation of isobaric interferences from Ba, Ce, Nd, Pr and Zr, all prepared in the same matrix. Multi-elemental calibration solutions were prepared at concentrations 5, 10 and 20 μg/ml. Data reduction and Quality control Mass-spectral data were collected as counts per second using Mass Hunter (Agilent) software and reduced through home-developed spread sheet (CODES, UTAS) using Excel Software (Microsoft Corporation). Reduction includes corrections by isobaric interferences, background and digestion procedure blank contribution, instrumental drift and dilution. Quantification includes a secondary correction by linear regression on three standard referenced materials (SRM), namely TASGRAN, TASBAS and AGV-1. The overall analytical uncertainty was estimated for each analysis. In addition, the data quality, precision and accuracy, can be estimated on replicates for the analysed unknown samples and a very well-known SRM, basalt BCR-2, as it has a similar matrix to the analysed samples. For further details see http://dx.doi.org/doi:10.26179/5d5cbdb0f2e52. Elements analysed Li, Be, Sc, Ti, V , Cr, Mn, Co, Ni, Cu, Zn, As, Rb, Sr, Y , Zr, Nb, Mo, Ag, Cd, Sn, Sb, Te, Cs, Ba, REE (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), Hf, Ta, W , Tl, Pb, Bi, Th, U Reagents usedSeastar BASELINE high purite grade (Seastar Chemicals Inc, USA), Type-I Mili-Q ultrapure water (Merk Millipore) and high purity standards (HPS) (CHOICE Analytical). Environment for sample preparation Clean lab class ISO5.