Re–Os systematics of UB-N, a serpentinized peridotite reference material

Abstract

The reference material (RM) UB-N is a typical representative of earth's upper mantle. It is a serpentinized garnet and spinel-bearing peridotite (a metamorphosed lherzolite) from the Vosges mountains, France, that is well characterized for major and many trace elements. In order to test whether UB-N is a suitable Re–Os reference material, 32 digestions in three different laboratories (CRPG/CNRS, MPI (Mainz) and University of Leoben) with four different digestion techniques (low-temperature acid attack, Carius tube dissolution, high-pressure asher (HPA-S) acid attack and alkali fusion) were performed. The results show that the low-temperature acid attack is unsuitable for the study of the Re–Os systematics of UB-N. Surprisingly, the well-established Carius tube acid digestion technique also fails to completely digest all Os-bearing mineral phases. Only alkali fusion and HPA-S acid attack yield the highest Os concentrations. Though sample inhomogeneity has been recognized (approximately 6% RSD for 2-g sample aliquots), it is possible to determine a well-defined average Os concentration of 3.85±0.13 ng g −1 (95% confidence; 19 digestions, fusion and HPA-S only). Rhenium-bearing minerals are very homogeneously distributed and replicates within each laboratory yield highly reproducible results independent of the digestion technique. A value of 0.2095±0.0040 ng g −1 (95% confidence; n=24) is assigned to the Re concentration. The best estimate for the whole-rock 187Os/ 188Os is 0.1278±0.0002 (95% confidence; n=12). The UB-N reference material now has well-understood Re–Os systematics that are typical of fertile upper mantle rocks. Analysis of this standard is, thus, highly recommended for the validation of Re–Os analytical procedures.