Elsevier

Chemical Geology

Volume 104, Issues 1–4, 10 February 1993, Pages 293-300
Chemical Geology

Isotope geoscience section
New constraints on the 138La β-decay constant based on a geochronological study of granites from the Yilgarn Block, Western Australia

https://doi.org/10.1016/0009-2541(93)90158-FGet rights and content

Abstract

The β-decay constant of 138La has been geochronologically determined using Archean granites from the Yilgarn Block, Western Australia. RbSr and SmNd mineral isochron ages were obtained for the two granite samples, which are nearly identical with the ion microprobe UPb zircon ages. This agreement indicates that the closure date for these samples is the same, within analytical error, making them suitable for geochronological estimation of the β-decay constant for 138La. Applying a new method of Ce isotope analysis, with analytical reproducibility of ±0.008%, LaCe isotope data for the studied samples resulted in precise mineral isochrons. Based on these internal mineral isochrons and ages determined by other geological clocks, the β-decay constant for 138La was estimated to be (2.33 ± 0.24)·10−12a−1 (2σ).

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