Tracing crustal contamination of the Cenozoic basalts with OIB-affinity in northern marginal region of North China Craton: An Os perspective

The Cenozoic basalts with OIB-affinity in northern marginal region of the North China Craton are thought to experience minor even no crustal contamination during the magma evolution. The whole-rock Sr-Nd-Pb-Hf isotopes are attributed to a two-component mixing between depleted and enriched mantle sources, while the major element variations are controlled by the fractional crystallization of olivine and clinopyroxene. However, in this study, the new Os isotopic data proposes an opposite model for the Cenozoic basalts in northern marginal region of the North China Craton. In this model, the Jining basalts were contaminated by the Archean mafic rocks during the magma storage and ascent. The crustal contamination process is supported by (1) the highly radiogenic Os isotopic compositions, and (2) the positive correlation between ¹⁸⁷Os/¹⁸⁸Os and 1/Os of the Jining basalts. By modeling the Os isotopic composition of the basalts, an incorporation of < 10% mafic granulites/amphibolites to the parental magma can successfully explain the initial values of highly radiogenic Os. In contrast, the unradiogenic and uniform Os isotopic compositions of the Chifeng basalts suggest negligible crustal contamination. Os isotopic data acts as an indicator of crustal contamination during magma evolution, providing us a novel insight into the evolution of the intra-continental OIB-like basalts worldwide.©2021 China Geology Editorial Office.