Research and Preliminary Application of Re-Os Isotope System for Limestone Samples

Sampling and digestion methods for Re-Os isotope analysis are improved for limestone samples. Hydrochloric acid was added to Carius tube to react with limestone in order to release CO₂. Then the Carius tube was sealed after adding oxidant reagent and spikes. Re-Os isotope system of the limestone, hosted on the bottom of Jiushidao formation of the Permian stratum at Yushu, Qinghai Province, was firstly analyzed worldwide by using this method. The obtained accurate age of (283.1±7.1) Ma (MSWD=0.61, Model 1, n=7) is consistent with the geological setting of the Schwagerina bearing stratum and especially the age U-Pb zircon dates for magmatic rocks. ¹⁸⁷Os/¹⁸⁸Os initial ratio obtained is 0.56±0.12, in agreement with the ¹⁸⁷Os/¹⁸⁸Os value of Permian seawater. Reasonable Re-Os isotopic age and initial Os value are obtained showing the closure of Re-Os isotope system in Limestone is perfect. Concentrations of Re and Os are positively correlated with organic carbon, which indicates Re and Os occur in the organic matter of limestone. This application provides a new tool for the stratigraphic classification and correlation.