Neotectonics in the Southwest Sub-basin, South China Sea: Constraints from multi-channel seismic data and IODP Expedition 349

Abstract:

The neotectono-sedimentary processes of the South China Sea abyssal basin have long been a puzzling issue and are still debated because of the lack of drilling evidence. In this study, we interpreted four multi-channel seismic profiles across the Southwest Sub-basin (SWSB), integrated for stratigraphic correlation with new drilling data from the Integrated Ocean Discovery Program （IODP） 349 Expedition. Results show that the Neogene sediments are divided into four stratigraphic units, each with distinctive seismic reflectors. Analysis of sedimentation rates and lithology suggests the sedimentary processes were climate dominated. Winter monsoon strength and increased aridity in the late Miocene limited accumulation rates in the SWSB, and summer monsoons and a variable glacial-interglacial climate since the Pliocene enhanced accumulation rates in the SWSB. Although the SWSB experienced NE–SW propagated spreading, terrigeneous sediments in the SWSB more likely originated from the southwest.

Three basement domains are classified with different sedimentary architectures and basement structures, including hyper-stretched crust, exhumed mantle, and steady state oceanic crusts. The SWSB experienced asymmetry geometry with detachment faulting in the final stage of continental rifting and exhumation of continental mantle lithosphere. Lithospheric breakup occurs after that of the crust, and the establishment oceanic spreading center and steady state crust production is delayed.