New insight into East Asian tectonism since the late Mesozoic inferred from erratic inversions of NW-trending faulting within the Bohai Bay Basin

The stress state and its dynamic background of East Asia, especially that during the late Mesozoic, remain controversial. We analyze the structural evolution of the Bohai Bay Basin (BBB) and it relationship with the regional tectonic history of East Asia. In particular, we focus on the central BBB NW-trending faults that have received little attention due to their inconspicuous structural features. Here we show that the erratic inversion of these NW-trending faults records episodic crustal deformation that is crucial for better understanding the regional tectonism. We find that these faults experienced alternating phases of shortening, stretching and shearing deformation. They initiated as reverse faults during the Late Triassic and reversed to normal faults during the Early Cretaceous. The pre-existing faults determined the development of NW-trending basins, which are synchronous with the peak destruction period of the North China Craton (NCC). The Late Cretaceous marks a stage of regional shortening without magmatism, which we propose to reflect a previously unrecognized period of flat-slab subduction of the Izanagi Plate. During the Early Paleogene (65–40 Ma), the reactivation of the NW-trending faults, likely due to the rollback of the oceanic slab, caused intensive rifting of the basin. During the Late Paleogene (40–23 Ma), they transformed to transtensional faulting due to the north-south oblique stretching from the parallel dextral strike-slip bounding faults. From Neogene, the basin entering its post-rift stage was characterized by the conjugate NE- and NW-trending strike-slip fault systems, likely in response to E-W regional compression.