Introducing a Comprehensive Data Reduction and Uncertainty Propagation Algorithm for U-Th Geochronometry with Extraction Chromatography and Isotope Dilution MC-ICP-MS

Ali Pourmand, François L.H. Tissot, Monica Arienzo, Arash Sharifi

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

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 from matrix elements through a single U/TEVA extraction chromatography step. A rigorous calibrator-sample 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, and were consistent with literature values within uncertainties. Based on multiple dissolutions with lithium metaborate flux fusion, U and Th concentrations in USGS BCR-2 CRM were updated to 1739 ± 2 and 5987 ± 50 ng g-1 (95% CI), respectively. The measurement 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.

Original languageEnglish (US)
Pages (from-to)129-148
Number of pages20
JournalGeostandards and Geoanalytical Research
Volume38
Issue number2
DOIs
StatePublished - Jun 2014

Keywords

  • MC-ICP-MS
  • Monte Carlo simulation
  • Speleothem
  • U-Th geochronometry
  • Uncertainty propagation

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

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