The nature of Neoproterozoic magmatism in the northeastern Yangtze Craton: Implications for breakup of Rodinia supercontinent

Abstract

Rocks recording Neoproterozoic geological events related to the Precambrian supercontinent cycle are widely distributed in the Yangtze Craton, and can be used to investigate the evolution of the craton in the context of supercontinent assembly-breakup. However, the paucity of systematic research into Neoproterozoic magmatism and sedimentation in the northeastern Yangtze Craton has hindered our understanding of the evolution of Yangtze Craton. In this study, middle Neoproterozoic magmatic and sedimentary rocks from the Zhangbaling Uplift were analysed to investigate the tectonic development of the northeastern Yangtze Craton and its relationship to the evolution of the Rodinia supercontinent. The results of petrographic and geochronological analyses indicate that the samples record two main stages of silicic magmatism (807–787 Ma granitic gneisses and 757–740 Ma quartz-keratophyres), and that proximal sedimentary rocks deposited at 662 Ma. The granitic gneisses and quartz-keratophyres exhibit the geochemical characteristics of typical A-type granites, with high contents of total-alkalis and HFSEs, suggesting an extensional tectonic setting during their formation. The main residual minerals in the rocks are garnet (gneisses) and plagioclase (keratophyres), reflecting the different depths of partial melting of the source rocks. The gneisses and keratophyres have contrasting zircon Lu-Hf isotopic components (εHf(t) = −29.9 to −11.8; −5.8 to 2.5). These lines of evidence imply a crustal structure comprising ancient lower crust and juvenile middle-upper crust. The particular crustal structure is obviously different from adjacent Dabie-Sulu orogenic belt, hinting Zhangbaling Uplift is an in-situ uplift zone. The magmatic evolution recorded by the granitic gneisses and quartz-keratophyres reflects a progression through different stages of continental rifting, from initial extension to mature rifting during the breakup of Rodinia supercontinent. In addition, the prominent affinity between low δ18O magmatism and sedimentation in the Yangtze and India Craton implies that the Yangtze Craton was located on the margin of Rodinia supercontinent prior to breakup.