Initiation of the Paleo‐Pacific Plate Subduction: Insights From Mesozoic Deformation and Tectonic Transition in the South China Block

ABSTRACT The onset of the Paleo‐Pacific subduction beneath the South China Block (SCB) remains controversial. This study addresses this issue by analysing the Mesozoic tectonic transition from the E–W‐trending Tethyan tectonic domain to the NE–SW‐trending Paleo‐Pacific tectonic domain within the SCB. Based on comprehensive field investigations conducted across the eastern, central and western segments of the SCB, this study systematically characterises the structural deformation patterns and constrains the timing of tectonic events in these regions. In the western SCB (Xuefengshan intercontinental tectonic system), a Triassic transition is evidenced by a shift from E–W to NNE‐trending folds, as well as the diachronous nature, indicating an east‐derived force. Fault‐strata relationships and Ar–Ar dating indicate that this eastward‐propagating deformation front was active during the Early–Middle Jurassic in the Middle–Lower Yangtze area and during the Middle–Late Jurassic in the southeastern coastal area. A suite of NE‐trending thrust‐nappes, diverse folds (box, chevron, comb and trough), and strike‐slip faults developed in the Middle–Lower Yangtze and southeastern coastal areas during the Early Yanshanian (J 1 –J 2 ). These eastern regions record SE–NW compression from thrust‐nappe systems and folds, unequivocally linking the eastward‐younging tectonic transition to the progressive subduction of the Paleo‐Pacific Plate. Consequently, these findings robustly support a Late Triassic initiation for the Paleo‐Pacific subduction beneath the South China Block.