An Inter-Laboratory Assessment of the Th Isotopic Composition of Synthetic and Rock Standards.

We present a concerted international effort to cross-calibrate five synthetic Th isotope standards (UCSC Th 'A'; OU Th 'U'; WUN; IRMM35; and IRMM 36), and six rock standards (UCSC TML, Icelandic ATHO; USGS BCR-2; USGS W2; USGS BHVO-2; LV18) using plasma ionization multi-collector inductively coupled mass spectrometry (PIMMS). We then compare our new values with the compilation of the literature mass spectrometric data for these standards and derive recommended 'consensus' 230Th/232Th values for each. We also present isotope dilution U and Th concentration data for four rock standards (UCSC TML, Icelandic ATHO; USGS BCR-2; USGS W2).