Intracontinental deformation of South China driven by Cretaceous Neotethyan subduction: evidence from the Tanlian ductile Shear Zone, Yunkai Massif

Understanding the geodynamic drivers of intracontinental deformation remains a fundamental challenge in continental dynamics. Situated at the intersection of the Palaeo-Pacific and Tethyan tectonic domains, the South China Block experienced widespread deformation and magmatism during the Cretaceous, yet their driving mechanisms remain debated. Here, we integrate macro- and microstructural observations, quartz ⟨c⟩-axis fabric analyses, and 40Ar/39Ar geochronology from the Tanlian Shear Zone in the southwestern Yunkai Massif to constrain its tectono-dynamic evolution. The Tanlian Shear Zone strikes NWW within the Ningtan Granite and records dominant dextral strike-slip kinematics. Microstructures and quartz fabrics indicate an early high-temperature deformation stage (peak > 600°C) overprinted by medium- to low-temperature brittle–ductile deformation. Mica 40Ar/39Ar ages from granitic mylonites constrain shear zone activity to 106–92 Ma. Together with coeval pull-apart basins and near N–S-trending magmatic dikes along the Bobai–Cenxi Fault Zone, these results indicate that regional deformation and magmatism were controlled by a near N–S-oriented compressional stress regime during the late Early to early Late Cretaceous. We interpret this stress field to have been primarily driven by northward subduction of Neo-Tethyan oceanic lithosphere, while the Palaeo-Pacific Plate exerted a subordinate influence due to contemporaneous slab rollback.