Geochronology and geochemistry of Early Jurassic volcanic rocks in the Erguna Massif, northeast China: Petrogenesis and implications for the tectonic evolution of the Mongol–Okhotsk suture belt

Abstract

The Mongol–Okhotsk suture belt played an important role in the tectonic evolution of northeast Asia during the Mesozoic. However, few studies have examined the influence of this tectonic belt on the geological evolution of northeast China. In this paper, we present zircon U–Pb geochronology, major and trace element geochemistry, and zircon Hf–O isotopic data for Early Jurassic volcanic rocks in the Erguna Massif of northeast China, with the aim of constraining the evolution of the Mongol–Okhotsk suture belt and its influence on the tectonic history of China during the Early Jurassic. Zircon U–Pb dating indicates that the trachybasalt and basaltic andesite in the study area were erupted between 193±5Ma and 181±9Ma (i.e., in the Early Jurassic). These Early Jurassic volcanic rocks belong to the high-K calc-alkaline series and are enriched in large ion lithophile elements and light rare earth elements, as well as being depleted in heavy rare earth elements and high field strength elements such as Nb and Ta. The rocks show a small negative Eu anomaly. The zircon εHf (182Ma) values of the volcanic rocks range from −1.9 to +5.1, corresponding to TDM1 values of 640–901Ma and TDM2 values of 901–1345Ma. Zircons from two volcanic rocks yield δ18O values of 7.2‰±1.5‰ (n=19) and 6.6‰±0.7‰ (n=35). Geochemically, these Early Jurassic volcanic rocks are similar to those from active continental margin settings, and their primary magmas could have been derived from the partial melting of a lithospheric mantle wedge modified by fluid from a subducted slab. The discovery of Early Jurassic calc-alkaline volcanic rocks in the Erguna Massif, together with the coeval porphyry Cu–Mo deposits, indicates that an active continental margin existed in the Erguna area during the Early Jurassic. Taken together, we conclude that southward subduction of the Mongol–Okhotsk oceanic plate took place beneath the Erguna Massif during the Early Jurassic.