Segment acceleration: 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 major 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 array through the middle Jiangnan orogen and western Cathaysia Block, employing a new 3D electrical resistivity model. In contrast to previous resistivity models applied across eastern and western Jiangnan, our adopted model revealed a thick high-resistivity electrical lithosphere of middle Jiangnan and a steep low-resistivity boundary on the east of Jiangnan lithosphere. 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 sections with different characteristics. Combined with previous observations, we propose a segment 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.