Strontium and Neodymium Isotopes

Abstract

The chapter presents data on Rb–Sr and Sm–Nd TIMS analysis of pyroxenes, plagioclases, gross samples of igneous rocks and sulphide ores. In most Sm–Nd analyses of minerals, the isotope system (pyroxene–plagioclase) does not reflect the age of intrusions and shows a rejuvenated or aged isochronous age. Only for the Kharaelakh intrusion, one 241 ± 32 Ma isochron was obtained, close to the U–Pb age of zircons. The primary isotope ratio ⁸⁷Sr/⁸⁸Sr and the ε_Nd parameter of samples are calculated for the age of 250 Ma based on the average U–Pb age of zircons. The primary ratio of plagioclases strontium from magmatic rocks of intrusions (0.7032–0.7090) is lower than that of ore sulphides (0.7081–0.7116). The heterogeneity of Sr and Nd isotope composition of minerals and rocks within a single intrusion is caused by different degrees of impact of ore and host-rock contamination. In the gross samples of igneous rocks from the studied massifs, the primary ratio of strontium varies from 0.7049 to 0.7128, and ε_Nd varies from −7.7 to +7.0. These data indicate a significant effect of the crustal component in the formation of igneous rocks during the injection of mantle material with the parameters ⁸⁷Sr/⁸⁸Sr = 0.7037 and ε_Nd = +9.5. Based on Nd and Sr isotopic data, it is impossible to clearly distinguish groups of intrusions with different ore content.