ABSTRACT

Osmium and Reabundance and ¹⁸⁷Os/¹⁸⁸Os ratios of reference rocks, JB-1a, JA-2 and JP-1, were determined through isotope dilution—negative thermal ionization mass spectrometry (ID-NTI-MS). Duplicate analyses of each sample show heterogeneous distribution of Re and Os in the reference rocks. The ranges of Re and Os concentrations are 150–200 and 9–12 ppt for JB-1a, 59–67 and 10–12 ppt for JA-2 and 28–32 and 2400–2700 ppt for JP-1, respectively. Extremely high ¹⁸⁷Os/¹⁸⁸Os ratios of 0.20–0.28, much higher than that of the chondritic mantle (0.12–0.13), of JB-1a and JA-2 indicates involvement of components with highly radiogenic ¹⁸⁷Os/¹⁸⁸Os ratios such as the subducting slab-derived materials. The reference rocks JP-1, Horoman peridotite, yields sub-chondritic Os isotopic composition of 0.12.