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Introducing a Comprehensive Data Reduction and Uncertainty Propagation Algorithm for U-Th Geochronometry with Extraction Chromatography and Isotope Dilution MC-ICP-MS
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| Organization: | The University of Miami |
| Department: | Neptune Isotope Laboratory (NIL), Division of Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Science (RSMAS) |
| Organization: | The University of Chicago |
| Department: | Origins Laboratory, Department of the Geophysical Sciences |
| Organization: | The University of Miami |
| Department: | Neptune Isotope Laboratory (NIL), Division of Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Science (RSMAS) |
| Organization: | The University of Miami |
| Department: | Neptune Isotope Laboratory (NIL), Division of Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Science (RSMAS) |
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| Geostandards and Geoanalytical Research |
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We present an open-source algorithm in Mathematica application (Wolfram Research) with a transparent data reduction and Monte Carlo simulation of systematic and random uncertainties for U-Th geochronometry by multi-collector ICP-MS. Uranium and thorium were quantitatively separated frommatrix elements through a single U/ TEVA extraction chromatography step. A rigorous calibratorsample bracketing routine was adopted using CRM-112A and IRMM-035 standard solutions, doped with an IRMM- 3636a 233U/236U ‘double-spike’ to account for instrumental mass bias and deviations of measured isotope ratios from certified values. The mean of 234U/238U and 230Th/232Th in the standard solutions varied within 0.42 and 0.25‰(permil) of certified ratios, respectively, andwere consistent with literature values within uncertainties. Based on multiple dissolutions with lithium metaborate flux fusion, U and Th concentrations in USGS BCR-2 CRMwere updated to 1739 ± 2and5987 ± 50 ng g-1 (95%CI), respectively. Themeasurement reproducibility of our analytical technique was evaluated by analysing six aliquots of an in-house reference material, prepared by homogenising a piece of speleothem (CC3A) from Cathedral Cave, Utah, which returned a mean age of 21483 ± 63 years (95% CI, 2.9‰). Replicate analysis of ten samples from CC3A was consistent with ages previously measured at the University of Minnesota by single-collector ICP-MS within uncertainties.
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