Intracontinental deformation and paleo-stress fields of the lower yangtze region during the late Mesozoic: implications for the tectonic evolution of South China

The late Mesozoic intracontinental deformation in South China preserves rich insights into continental evolution, with close link to subduction and collision processes along the eastern margin of the Eurasian Plate. The Lower Yangtze Region, located in the northeastern part of South China, underwent complex intracontinental deformation during the late Mesozoic, making it a key area for understanding the tectonic evolution of East Asia. Through detailed field investigation of representative outcrops and structural analysis of fault-slip data from the regional faults, this study reconstructs the late Mesozoic deformation sequence and paleo-stress fields in the Lower Yangtze Region. Our new data, combined with published results, suggest that the Lower Yangtze Region experienced a three-stage tectonic evolution from the Late Jurassic to early Late Cretaceous, characterized by alternating contractional and extensional tectonic events. The first stage, contractional deformation from the Late Jurassic to early Early Cretaceous, was controlled by NW-SE contractional stress, generating sinistral strike-slip motion along the Tan-Lu Fault, the dextral strike-slip motion along the Chuhe Fault and Yangtze River Fault, and top-to-west thrusting of the Maoshan Fault. This contractional deformation is interpreted as being related to the westward low-angle subduction of the Paleo-Pacific Plate beneath the Eurasian Plate. The second stage is NW-SE extension during the Early Cretaceous, associated with a series of high-angle normal faults, which is correlated with the rollback of the Paleo-Pacific Plate. The third stage is another episode of contractional deformation that resulted in a tectonic inversion controlled by nearly N-S contraction during late Early Cretaceous to early Late Cretaceous. This contraction led to the sinistral strike-slip motion of the regional faults and was associated with a set of conjugate strike-slip faults. The oblique collision between the Okhotomorsk Block and the Eurasian Plate serves as the geodynamic driver for this contraction event. Comparative structural analysis reveals distinct deformation patterns between the Lower Yangtze Region and other areas of South China during the Late Jurassic to early Early Cretaceous. Under the same NW-SE contraction, the Lower Yangtze Region exhibited predominant strike-slip motion along the major faults, whereas other areas of South China developed NNE-SSW-striking thrust-and-fold deformation. This disparity is possibly caused by the unique tectonic position and pre-existing basement faults of the Lower Yangtze Region. Due to the obstruction of the rigid craton (i.e., the North China Craton), the crustal materials underwent lateral extrusion towards the northeast along the pre-existing faults, accommodating the continuous contraction that occurred during the Late Jurassic to early Early Cretaceous.