Zircon M257 - a homogeneous natural reference material for the ion microprobe U-Pb analysis of zircon

Nasdala, Lutz and Hofmeister, Wolfgang and Norberg, Nicholas and Mattinson, James M. and Corfu, Fernando and Dörr, Wolfgang and Kamo, Sandra L. and Kennedy, Allen K. and Kronz, Andreas and Reiners, Peter W. and Frei, Dirk and Kosler, Jan and Wan, Yusheng and Götze, Jens and Häger, Tobias and Kröner, Alfred and Valley, John W. 2008. Zircon M257 - a homogeneous natural reference material for the ion microprobe U-Pb analysis of zircon. Geostandards and Geoanalytical Research 32: pp. 247-265.

Source Title

Geostandards and Geoanalytical Research

Faculty

School of Science and Computing

Faculty of Science and Engineering

Department of Imaging and Applied Physics

Remarks

URI

http://hdl.handle.net/20.500.11937/47515

Collection

Curtin Research Publications

Abstract

We introduce and propose zircon M257 as a future reference material for the determination of zircon U-Pb ages by means of secondary ion mass spectrometry. This light brownish, flawless, cut gemstone specimen from Sri Lanka weighed 5.14 g (25.7 carats). Zircon M257 has TIMS-determined, mean isotopic ratios (2s uncertainties) of 0.09100+_ 0.00003 for 206pb/238U and 0.7392+_0.0003 for 207pb/235U. Its 206pb/238U age is 561.3+_0.3 Ma (unweighted mean, uncertainty quoted at the 95% confidence level); the U-Pb system is concordant within uncertainty of decay constants. Zircon M257 contains ~ 840 μg g-1 U (Th/U ~ 0.27). The material exhibits remarkably low heterogeneity, with a virtual absence of any internal textures even in cathodoluminescence images. The uniform, moderate degree of radiation damage (estimated from the expansion of unit-cell parameters, broadening of Raman spectral parameters and density) corresponds well, within the "Sri Lankan trends", with actinide concentrations, U-Pb age, and the calculated alpha fluence of 1.66 x 1018 g-1. This, and a (U+Th)/He age of 419+_9 Ma (2s), enables us to exclude any unusual thermal history or heat treatment, which could potentially have affected the retention of radiogenic Pb. The oxygen isotope ratio of this zircon is 13.9%o VSMOW suggesting a metamorphic genesis in a marble or calc-silicate skarn.