HR: 0800h
AN: V51C-0599    [Abstracts]
TI: In-situ Pb Isotope Ratio Measurements in Glasses and Melt Inclusions by LA-SF-ICPMS
AU: * Jochum, K P
EM: kpj@mpch-mainz.mpg.de
AF: Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany
AU: Stoll, B
AF: Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany
AU: Herwig, K
AF: Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany
AU: Amini, M
AF: Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany
AU: Abouchami, W
AF: Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany
AB: We have developed a technique to determine Pb isotopes in glass fragments and melt inclusions by laser ablation (LA) - sector field (SF) - ICPMS. The measurements were done with a New Wave UP-213 laser system and an ELEMENT2 ICP mass spectrometer using the electrical scan mode. The geological MPI-DING reference glasses (Jochum et al., 2000), for which TIMS and MC-ICPMS Pb triple spike (TS) data are now available, were used to test our technique. Our LA-SF-ICPMS data for $^{208}$Pb/$^{206}$Pb and $^{207}$Pb/$^{206}$Pb agree with the high-precision Pb data within 0.2 %. Polished 150 $\mu$m thick sections were used for the analysis of melt inclusions from samples of the Hawaii Scientific Drilling Project (HSDP). Inclusions were ablated for 10 - 30 s in single spots (40 - 80 $\mu$m diameter). Each analysis consisted of 100 to 300 measurements of $^{206}$Pb, $^{207}$Pb and $^{208}$Pb. Typical in-run precision (1 RSE) ranged from 0.2 - 0.4 %. These values are similar to those obtained by SIMS (Saal et al., 1998). The $^{208}$Pb/$^{206}$Pb (1.91 - 2.13) and $^{207}$Pb/$^{206}$Pb (0.778 - 0.877) in the melt inclusions show large and systematic variations. The range of variability in Pb isotope ratios is similar to that reported in melt inclusions from Mangaia and Tahaa basalts (Saal et al., 1998). The Pb isotope arrays (in $^{208}$Pb/$^{206}$Pb vs $^{207}$Pb/$^{206}$Pb) can be explained by mixing of at least two end members. Groundmass values are uniform and similar to the whole rock data and plot within the melt inclusion fields. LA-SF-ICPMS has also been applied for determining Pb isotope ratios and trace element concentrations in carefully handpicked 200 - 500 $\mu$m large glass fragments from 19 samples of the submarine section of HSDP-2. Precision of the Pb isotope data was about 0.2 - 0.3 %. Most LA-SF-ICPMS data agree with high-precision TIMS data using aliquots of about 50 mg. Both data sets confirm the temporal Pb isotope variations found in the HSDP-2 core based on the whole-rock TS Pb isotope data (Eisele et al., 2003).
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
DE: 1094 Instruments and techniques
DE: 1010 Chemical evolution
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting