The Re-Os isotopic system: geochemistry and methodology at the Geochronological Research Center (CPGeo) of the University of São Paulo, Brazil

Abstract

The Re-Os isotopic system is an important tool for the study of mantle-crust processes, geochronology and the tracing of source reservoirs for metal deposition. Rhenium and osmium differ fundamentally from other lithophile isotopic systems with regards to their behavior during partial melting processes, coupled with the chalcophile/siderophile nature of both elements. These differences make the system extremely useful for a number of novel applications not traditionally addressed by lithophile isotopic systems. A low-blank technique for the analysis of Re-Os isotopes in geological materials has been established at the Geochronological Research Center (CPGeo) of the Geosciences Institute of the University of São Paulo, Brazil, with the aim of furthering knowledge of regional geology, tectonic evolution, petrology and ore deposition in South America. The techniques described here use isotope dilution to simultaneously determine the concentration of Os and Re as well the Os isotopic composition of geologic materials. Sample digestion and sample-isotopic spike equilibration are achieved in sealed borosilicate glass tubes at high temperature. Osmium is separated and purified by carbon tetrachloride solvent extraction and micro-distillation techniques. Rhenium is separated and purified by anion exchange chromatography. Accuracy of the concentration and isotopic determinations is monitored by the analysis of a certified reference material (WPR-1) and the use of the Department of Terrestrial Magnetism (DTM) Os isotopic standard. Measured values and precision of these standards is within error and comparable to established Re-Os laboratories.