Revisiting Neoproterozoic tectono-magmatic evolution of the northern margin of the Yangtze Block, South China

The Neoproterozoic tectonics of the Yangtze Block is crucial for understanding its evolution history over the assembly and disintegration of the supercontinent Rodinia. Herein, we integrate all the published geochemical and geological data for igneous rocks of 1.0-0.6 Ga from the northern margin of the Yangtze Block to investigate the secular tectonic evolution of the Yangtze Block. The results show that the early Neoproterozoic intra-oceanic subduction could have initiated at ca. 1.0 Ga, which was followed by the flare-up of continental arc magmatism since -0.9 Ga along the northern margin of the Yangtze Block. Crustal reworking was enhanced during episodes of subduction compression at ca. 0.86 Ga and 0.83 Ga, respectively, revealed by the striking decrease in zircon epsilon Hf(t) and whole-rock epsilon Nd(t) values. The gradual progression to depleted mantle-like isotopic signatures during 850-840 Ma and 820-810 Ma reflects the diminishing subduction-induced enrichment in the mantle source as the tectonic setting altered to the extensional back-arc modes shortly after the compressional phases. The secular isotope pattern during the continental arc stage (0.9-0.8 Ga) implies alternative regimes of compressive and extensional tectonics, which were accompanied with synchronous changes in crust thickness. After -0.8 Ga, the northern margin of the Yangtze Block evolved into distinct tectonics in different regions. The 0.8-0.73 Ga magmatism in the northeastern domains displays both within-plate and arc-like geochemical affinities, as well as exclusively low delta 18O signatures, suggesting a predominantly continental rift setting. However, the widespread calc-alkaline I-type granitoids and contemporaneous arc-like mafic rocks in the northwestern domains demonstrate that the tectonic regime were still controlled by a continuous subduction process until the end of arc magmatism at ca. 0.73 Ga. Subsequently, the entire northern margin of the Yangtze Block gradually evolved into a volcanic rifted margin during 0.72-0.62 Ga as revealed by the deposition of massive syn-rift volcanic-sedimentary sequences and the emplacement of the contemporaneous mafic-ultramafic equivalents, probably as a response to the far-field effect of supercontinent breakup. Collectively, the prolonged (-1.0-0.73 Ga) suprasubduction magmatism along the northwestern of the Yangtze Block, together with the 0.97-0.82 Ga accretionary belt along the southeastern margin, likely indicates an external position of the South China Block in Rodinia.