TY - JOUR

T1 - Determination of ultra-low Nb, Ta, Zr and Hf concentrations and the chondritic Zr/Hf and Nb/Ta ratios by isotope dilution analyses with multiple collector ICP-MS

AU - Weyer, Stefan

AU - Münker, Carsten

AU - Rehkämper, Mark

AU - Mezger, Klaus

N1 - Funding information: We are grateful to the Max-Planck-Institut für Chemie in Mainz, Germany, for providing a Tantalum isotopic tracer, which led to the major progress of the present study. We thank the Institut für Planetologie, Münster, Germany and the Max-Planck-Institut für Chemie in Mainz, Germany for providing meteorite samples and geological standard reference material. We are grateful to E. S. Scherer (Münster) for critical reading of the manuscript. S. Weyer thanks A. Hofmann (Max-Planck-Institut für Chemie,) for financial support during the course of this study. J. Blichert-Toft and T.E. Jeffries provided helpful reviews. [RR]

PY - 2002/8/1

Y1 - 2002/8/1

N2 - This study presents a new technique for the determination of precise and accurate concentrations of the high field strength elements (HFSE) Zr, Hf, Nb and Ta. The Ta concentration was determined for the first time by the isotope dilution (ID) technique using an isotopic tracer enriched in 180Ta. Zirconium and hafnium concentrations were also determined by ID, whereas the concentration of the mono-isotopic Nb was measured relative to Zr, after quantitative separation of the HFSE from the matrix. The analyses were performed on a Micromass Isoprobe multiple collector (MC) inductively coupled plasma source mass spectrometer (ICP-MS). Only about 0.5 ng of Zr, Hf and Ta are necessary to perform an ID analysis with an external reproducibility of better than 1% on the MC-ICP-MS using Faraday collectors. This new technique enables the precise and accurate determination of the HFSE concentrations even in ultra-depleted rocks like peridotites. The absolute uncertainties for ultra-depleted rocks, particular for Ta concentrations at the sub-ng level are limited by blanks and sample heterogeneities and not by the precision of the measurement. New and more precise Zr, Hf, Nb and Ta concentration data for the geological standard reference materials BHVO-2, BCR-2, BE-N, BIR-1 and the ultra-depleted standards PCC-1 and DTS-1 are presented. External reproducibilities of the concentration measurements are 0.4-5% for basalts and 2-10% for depleted peridotite samples (2 RSD), depending on element and concentration. The Zr/Hf and Nb/Ta ratio of the solar system was determined based on new data for two chondrites and six achondrites. The chondritic Nb/Ta of 17.6 ± 1.0 determined in this study agrees with previous predicted values from the literature. However, the chondritic Zr/Hf of 34.2 ± 0.3 determined in this study differs from previous literature values.

AB - This study presents a new technique for the determination of precise and accurate concentrations of the high field strength elements (HFSE) Zr, Hf, Nb and Ta. The Ta concentration was determined for the first time by the isotope dilution (ID) technique using an isotopic tracer enriched in 180Ta. Zirconium and hafnium concentrations were also determined by ID, whereas the concentration of the mono-isotopic Nb was measured relative to Zr, after quantitative separation of the HFSE from the matrix. The analyses were performed on a Micromass Isoprobe multiple collector (MC) inductively coupled plasma source mass spectrometer (ICP-MS). Only about 0.5 ng of Zr, Hf and Ta are necessary to perform an ID analysis with an external reproducibility of better than 1% on the MC-ICP-MS using Faraday collectors. This new technique enables the precise and accurate determination of the HFSE concentrations even in ultra-depleted rocks like peridotites. The absolute uncertainties for ultra-depleted rocks, particular for Ta concentrations at the sub-ng level are limited by blanks and sample heterogeneities and not by the precision of the measurement. New and more precise Zr, Hf, Nb and Ta concentration data for the geological standard reference materials BHVO-2, BCR-2, BE-N, BIR-1 and the ultra-depleted standards PCC-1 and DTS-1 are presented. External reproducibilities of the concentration measurements are 0.4-5% for basalts and 2-10% for depleted peridotite samples (2 RSD), depending on element and concentration. The Zr/Hf and Nb/Ta ratio of the solar system was determined based on new data for two chondrites and six achondrites. The chondritic Nb/Ta of 17.6 ± 1.0 determined in this study agrees with previous predicted values from the literature. However, the chondritic Zr/Hf of 34.2 ± 0.3 determined in this study differs from previous literature values.

KW - Chondritic ratio

KW - High field strength elements

KW - Isotope dilution

KW - Multiple collector ICP-MS

KW - Niobium

KW - Tantalum

UR - http://www.scopus.com/inward/record.url?scp=0036687070&partnerID=8YFLogxK

U2 - 10.1016/S0009-2541(02)00129-8

DO - 10.1016/S0009-2541(02)00129-8

M3 - Article

AN - SCOPUS:0036687070

VL - 187

SP - 295

EP - 313

JO - Chemical geology

JF - Chemical geology

SN - 0009-2541

IS - 3-4

ER -