Geochronology and geochemistry of early Paleozoic–early Mesozoic magmatic rocks from the Zhangguangcai Range, NE China: Constraints on the tectonic evolution of the eastern Songnen Massif

Abstract

This paper presents new zircon U–Pb–Hf isotopic and whole‐rock geochemical data for early Paleozoic–early Mesozoic igneous rocks from the Zhangguangcai Range, which are used to provide constraints on the petrogenesis and tectonic setting of these rocks and on the tectonic evolution of the eastern Songnen Massif. We dated five igneous rocks from the Zhangguangcai Range of the eastern Songnen Massif, namely, a late Cambrian (~489 Ma) syenogranite, a middle Silurian (~431 Ma) dacite, a Middle Triassic (~247 Ma) gabbro‐diorite and two Late Triassic (214–210 Ma) rhyolites. The late Cambrian syenogranite, middle Silurian dacite and Late Triassic rhyolites have high SiO2and (Na2O + K2O) contents and low Mg#values. These four rocks are enriched in light rare earth elements (LREEs) and large‐ion lithophile elements (LILEs) but depleted in heavy REEs (HREEs) and high‐field‐strength elements (HFSEs). In addition, the εHf(t) values and TDM2ages of zircons from these rocks range from −1.31 to +5.88 and from 1264 to 896 Ma, respectively. These data suggest that their primary magma was derived from partial melting of the juvenile mafic lower crust that was generated during the Mesoproterozoic–Neoproterozoic. The Middle Triassic gabbro‐diorite has low SiO2and high MgO, Sc, Co, Cr and Ni contents and is enriched in LILEs and LREEs but depleted in HREEs and HFSEs such as Nb and Ta. Combining these features with the zircon εHf(t) values of the gabbro‐diorite, which range from +0.02 to +1.79, the primary magma of this rock is inferred to have been derived from partial melting of an isotopically depleted lithospheric mantle. The late Cambrian syenogranites and the middle Silurian dacites are weakly peraluminous and are classified as medium‐ to high‐K calc‐alkaline series, indicating that they formed in an active‐continental‐margin setting. The Middle–Late Triassic igneous rocks exhibit a bimodal igneous rock association, suggesting that they formed within an extensional environment. Combining our new results with previous findings, the early Paleozoic–early Mesozoic tectonic evolution of the eastern Songnen Massif is revealed. During the early Cambrian–early Silurian, the oceanic plate between the southern Songnen and southern Jiamusi massifs subducted westward beneath the Songnen Massif. The amalgamation between the southern Songnen and southern Jiamusi massifs occurred during the middle Silurian, and the southeastern Songnen Massif was in a post‐collisional extensional setting during the Devonian. During the late Carboniferous–Triassic, the Zhangguangcai Range was in an extensional environment, and the Mudanjiang Ocean started to open along the Jiayin–Mudanjiang Fault, separating the Songnen and Jiamusi massifs during the Middle–Late Triassic.