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A simple method for in-situ U–Th–He dating

Vermeesch, Pieter; Sherlock, Sarah C.; Roberts, Nick; Carter, Andy. 2012 A simple method for in-situ U–Th–He dating. Geochimica et Cosmochimica Acta, 79. 140-147. 10.1016/j.gca.2011.11.042

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Abstract/Summary

This paper presents a significantly simplified method for in-situ U–Th–He dating removing the need to know any absolute concentrations. This is done by calculating the normalised U, Th, and He concentrations of a conventionally dated calibration standard from its measured Th/U ratio and known U–Th–He age, and scaling these concentrations to the raw U, Th, and He signals of the sample. The Th/U ratio of the standard can be determined from its measured 208Pb/206Pb ratio, removing the need to use NIST glass as a reference material. We introduce an LA-ICP-MS-based method to correct for variable ablation depths between the standard and the unknown, using the strength of the ablated 29Si signal. Finally, we propose a pseudo-depth profile method to assess the effects of compositional zoning on the accuracy of in-situ U–Th–He data. The effectiveness of the proposed method has been demonstrated on three samples of gem-quality Sri Lanka zircon, which yield ages that are in agreement with previously published conventional U–Th–He measurements.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.gca.2011.11.042
Programmes: BGS Programmes 2010 > NERC Isotope Geoscience Laboratory
ISSN: 0016-7037
Date made live: 10 Apr 2012 15:37
URI: http://nora.nerc.ac.uk/id/eprint/17636

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