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

作者：Vermeesch Pieter^*; Sherlock Sarah C; Roberts Nick M W; Carter Andy

来源：Geochimica et Cosmochimica Acta, 2012, 79: 140-147.

DOI：10.1016/j.gca.2011.11.042

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 (208)Pb/(206)Pb 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 (29)Si 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.

• 出版日期2012-2-15