Magnetotelluric Imaging of Slab Subduction and Rollback: Constraints on Mantle‐Driven Orogenic Evolution in the Jiangnan Orogen

Abstract The Neoproterozoic Jiangnan Orogen (JNO) in South China, a fundamental suture amalgamating the Yangtze and Cathaysia blocks, provides key insights into orogenic processes. However, poorly constrained lithospheric architecture in the central JNO sustains debates regarding the genesis of Neoproterozoic magmatism. Here, we present a high‐resolution, 3‐D resistivity model extending to 135 km depth, derived from broadband magnetotelluric data across the central JNO. The model reveals a predominantly resistive crust, disrupted by prominent conductors within the middle‐to‐lower crust beneath the Jiuling batholith. In the lithospheric mantle, a sharp electrical discontinuity coincides with the Early Neoproterozoic collisional zone (ca. 850–820 Ma), separating a resistive northwest from a conductive southeast. Integrated with geophysical and thermodynamic modeling, our findings suggest that present‐day partial melting beneath the Jiuling batholith is unlikely. Instead, the crustal conductors are interpreted as fossilized remnants of ancient tectono‐magmatic processes, likely representing trapped saline fluids or conductive mineral networks (e.g., graphite or sulfides). The upper mantle conductor is similarly interpreted as a fossilized subduction‐modified domain, potentially enriched in fluorine‐bearing phlogopite. Geodynamically, we propose that rollback and subsequent break‐off of the Paleo–South China Ocean slab induced substantial asthenospheric upwelling. This thermal perturbation drove extensive remelting of the thickened accretionary crust, generating the voluminous Jiuling granites. Our results delineate an integrated evolutionary pathway from oceanic subduction to mantle‐driven orogenesis, providing new insights into crustal maturation and Phanerozoic reactivation in ancient accretionary systems.