Mathematics – Logic
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusm.v41a..07a&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #V41A-07
Mathematics
Logic
1040 Radiogenic Isotope Geochemistry, 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 1094 Instruments And Techniques, 1105 Quaternary Geochronology
Scientific paper
The 202Pb-205Pb-233U-235U spike (Pb DS), prepared at the Geological Survey of Canada in 2005 [1], and the 202Pb-205Pb-235U spike, prepared at the Department of Geosciences, University of Oslo [2], have been used for more than two years. Both spikes are routinely used for TIMS analysis of Pb with internal fractionation correction for U-Pb dating of various rocks and minerals, including dating perovskite [2] and meteorites and their components [1, 4-7]. A few hundred standard and sample Pb DS analyses were acquired with these two spikes using Triton TI mass spectrometers at the Geological Survey of Canada, US Geological Survey and the Australian National University, a Finnigan-MAT 261 mass spectrometer at The University of Texas at Austin and a Finnigan-MAT 262 mass spectrometer at the University of Oslo. All analyses were performed using high efficiency silicic acid emitter [8] and a static multicollector mode if the samples were sufficiently large to produce an ion beam greater than ca. 2-5×10-14 A on 206Pb and 207Pb. These data allow us to evaluate long - term performance of the Pb DS procedure for sub-nanogram samples of Pb. The performance of this procedure is evaluated on the basis of the long-term reproducibility of analyses of isotopic standards, and from improving quality of linear fits in Pb-Pb isochron diagrams (and, hence, improved precision of ages) compared to the same data reduced using external normalization. The data for 0.3 ng loads of SRM-981, analyzed with the batches of samples in 2006 and 2007 at the GSC, yield the mean 204Pb/206Pb of 0.05904±0.00013 (0.226% 2σ), #207Pb/206Pb of 0.91483±0.00018 (0.020% 2σ)), and 208Pb/206Pb of 2.16771±0.00054 (0.025% 2σ)). These values and errors are similar to those reported in [1] for the loads of the same size, and to the values obtained for similar loads at the USGS and at ANU over shorter periods of time. The precision and reproducibility of sample analysis and standard analyses is similar, and depends mostly on the amount of Pb in the load. The quality of DS Pb analyses is demonstrated by a three-fold improvement in precision of the linear fit for the iron meteorite Cape York [9] compared to the same data reduced with external normalization, and by dates of angrites, eucrites and CAIs with precision between 0.12-0.30 Ma [3-7,9]. [1] Amelin Y. and Davis W.J. (2006) JAAS 21, 1053-1061, [2] Corfu F. and Dahlgren S. (2008) EPSL 265, 256-269, [3] Connelly J.N. et al. (2008) LPS- XXXIX, #2386, [4] Amelin Y. et al. (2006) LPS-XXXVII, #1970 [5] Amelin Y. (2008) GCA 72, 221-232, [7] Connelly J.N. et al. (2008) Astrophys. J., in press, [8] Gerstenberger H. and Haase G. (1997) Chem. Geol. 136, 309-312, [9] Connelly J.N. et al. submitted to GCA.
Amelin Yu.
Connelly James N.
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