Segmented accretion: new insights into the convergence between the Yangtze and Cathaysia blocks, as interpreted from 3D magnetotelluric imaging

Abstract As the Neoproterozoic suture zone between the Yangtze and Cathaysia blocks, the Jiangnan orogen is both a research hotspot and controversial issue. In particular, its formation process and tectonic polarity have been extensively investigated in recent years, leading to three kinds of geological interpretations, including southeastward subduction of the Yangtze block, northwestward subduction of the Cathaysia block and divergent double subduction. However, none of these interpretations can completely reconcile the abundant geological and geophysical data. Therefore, we performed a magnetotelluric profile across the middle Jiangnan orogen and western Cathaysia Block, and employed a new 3D electrical resistivity model. In contrast to previous resistivity models applied across eastern and western Jiangnan, our model revealed a thick lithosphere of middle Jiangnan with high resistivity and a steep low-resistivity boundary on the east. This structure indicates that the middle section of block convergence can be interpreted as a transitional region of polarity conversion rather than oceanic or continental subduction. Hence, we suggest that previous geological interpretations involving the subduction hypothesis are applicable to the convergence process in South China, but are only appropriate for local sections with different characteristics. Combined with previous observations, we propose a segmented accretion model, including southeastward subduction of the oceanic slab in eastern Jiangnan, northwestward subduction of the Cathaysia block in the west, and transitional accretion in the middle. Graphical Abstract