Sedimentary records of tectonic background transition in the eastern Guangdong Basin in the Late Early Jurassic of the South China continental margin

The southeastern margin of the South China Block preserves sedimentary records of tectonic evolution controlled by Paleo-Pacific subduction. This study integrates sedimentological and detrital zircon U-Pb geochronological analyses of the Lower Jurassic Qiaoyuan Formation in the eastern Guangdong Basin. One Late Early Jurassic sample exhibits detrital zircon U-Pb ages ranging from 2317 to 187 Ma, with dominant age groups at 260–240 Ma and 1900–1800 Ma. In contrast, a terminal Early Jurassic sample shows age spectra of 2827–180 Ma dominated by a 200–180 Ma group, reflecting a transition from multi-peak to unimodal age distributions. Provenance analysis indicates that late Early Jurassic sediments (Member 1) were primarily sourced from the Jiangnan Orogen, Yunkai Terrane, and Hainan Island, while terminal Early Jurassic deposits (Member 3) originated predominantly from the Nanling Tectonic Belt. Comparative analysis of detrital zircon age characteristics in Mesozoic strata across the South China Block, incorporating similarity assessments, visualization methods, and crustal thickness estimations, demonstrates that the southeastern margin completed the transition from a compressional to extensional tectonic setting by approximately 180 Ma. This shift is chronologically constrained by provenance reorganization, basin structural transformation, and progressive crustal thinning, documenting the dynamic interplay between Paleo-Pacific subduction and intracontinental deformation.