Magmatic records of subduction and closure of the Paleo-South China Ocean and subsequent rifting in the South China Block

The South China Block, which comprises the Yangtze and Cathaysia blocks amalgamated along the Jiangnan orogen, is key to understanding early to middle Neoproterozoic era tectonic evolution. However, the timing and subduction processes involved in the closure of the Paleo-South China Ocean (a northeast-southwest−trending Neoproterozoic ocean between the Yangtze and Cathaysia blocks), as well as the mechanism responsible for the subsequent lithospheric extension of the South China Block, remain poorly constrained. To address these issues, we integrated geological, geochronological, geochemical, and Sr-Nd-Hf-O isotope data from Neoproterozoic igneous rocks in the Jiangnan orogen. Our results reveal three distinct magmatic phases at ca. 876−837 Ma, ca. 823−820 Ma, and ca. 798−784 Ma. The ca. 876−837 Ma igneous rocks include andesites and A-type rhyolites with arc-type trace element compositions, and spilites with normal mid-ocean-basalt−type compositions. Spatial analysis suggests that the Dengshan andesites and Yifeng spilites likely formed in a backarc basin, whereas the Yifeng rhyolites and andesites probably formed in a forearc setting. This collectively suggests a pre-830 Ma forearc-arc-backarc system along the Jiangnan orogen. The ca. 820 Ma S-type granites, derived from mixed sources containing ancient sediments and juvenile materials, likely formed in a syn-collisional or postcollisional setting, which indicates that the Paleo-South China Ocean closed at ca. 830−820 Ma. This closure likely culminated in arc-continent and continent-continent collisional events that involved the Huaiyu oceanic arc, the Yangtze Block, and the Cathaysia Block. The subsequent ca. 798−784 Ma igneous rocks are bimodal in composition, which reflects a continental rift setting. Based on these data and regional correlations, we propose that the South China Block occupied the northwestern margin of Rodinia during the middle Neoproterozoic, and its tectonic evolution was shaped by oceanic closure, collisional orogenesis, and postcollisional extension.