Tectonic Evolution And Its Dynamic Process Of Cretaceous Volcanic Basins In The East Of South China

The Pacific subduction zone and the Tethyan subduction/collision zone border the South China Block along its eastern and western margins. The spatial and temporal interactions of these two orogenic systems induced widespread intra-continental deformation within the South China Block during the Mesozoic. Widespread Cretaceous volcanic basins are crucial to understand the tectonic evolution of South China. Lithostratigraphic units in these basins are grouped, in ascendant order, into the Early Cretaceous volcanic suite (K1v), the Yongkang Group (K1-2) and the Jinqu Group (K2). SHRIMP U-Pb zircon and LA-MC-ICPMS U-Pb zircon geochronological results suggest that (1) the Early Cretaceous volcanic suite (K1v) erupted at 136-129 Ma. (2)the Yongkang Group (K1-2) can be divided into two rock suites:the lower rock suite, consisting of the Guantou and Chaochuan Formations, was deposited at 124?112 Ma; while the upper rock suite, corresponding to the Fangyan Formation, was deposited at 104?91 Ma.(3) the deposition of the Jinqu Group (K2) postdated 91 Ma. Structural analyses of fault-slip data from these rock units delineate three cycles of tectonic evolution during the Early Cretaceous to Paleogene period. The first and second cycles were both dominated by alternating stress episodes of NW-SE extension and NW-SE compression. The third cycle was dominated by stress episodes of N-S extension and NE-SW compression. The NW-SE extension accommodated the initial opening and sediment infilling of the basin, which might possibly originate from the back-arc extension induced by the rollback of the subducted Paleo-Pacific slab during the Early Cretaceous. The NW-SE compression led to tectonic inversion, and was responsible for the unconformity between the Upper and Lower Cretaceous strata, which was probably associated with the variations of the subducted slab dynamics, or the collision between the eastern Asian margin and the West Philippine Block. The N-S extension led to the opening and synchronous sedimentation of Late Cretaceous basin, The NE-SW compression caused a second tectonic inversion of the basins during the Late Paleogene. The Neo-Tethyan subduction and subsequent Cenozoic India-Asia collision might provide plausible geodynamic interpretations for the Late Cretaceous N-S extension and the Early Paleogene NE-SW compression respectively.