Tectonic evolution of the South China Ocean-Continent Connection Zone: Transition and mechanism of the Tethyan to the Pacific tectonic domains

Abstract

The northern South China Sea continental margin is the key or critical segment of the Ocean-Continent Connection Zone (OCCZ) of the Great South China Block, the junction between the Tethyan and the (Paleo-) Pacific dynamic systems, and the interaction area between the Indian Ocean and the Pacific Ocean. However, due to the low-degree geophysical exploration in the past, the regional tectonic background, processes and mechanism of the transition between the Tethyan and the Pacific tectonic domains are unclear. Based on the latest large number of seismic profiles, we focus on the Cenozoic basin structure in the continental margin of the northern South China Sea and try to reveal the Mesozoic basement structures of the northern South China Sea continental margin, with the aim of exploring the pre-Cenozoic tectonic evolution and the Cenozoic opening, spreading, ridge fossil and closure of the South China Sea oceanic basin, so as to serve the accurate oil and gas exploration in this area at the same time. The seismic interpretation of the Pearl River Mouth Basin and the field structural investigation of the South China continental margin show that the OCCZ of the South China Block has experienced three processes: Mesozoic Indosinian collisional orogeny, Early Yanshanian accretionary orogeny and Late Yanshanian transpressive orogeny. During the Cenozoic era, it experienced the dispersive extension into basins under the control of NW-SE-directed normal extension in the early stage, the dextral pull-apart into basins under the control of NE-NNE-trending strike-slip faults in the middle stage, and the sinistral pull-apart into basins under the control of NW-WNW strike-slip faults in the late stage. In general, the transition process from the Tethyan to the Pacific tectonic systems can be subdivided into four stages: the transition from the Paleo-Tethyan to the Neo-Tethyan tectonic systems, the transition from the Neo-Tethyan to the Paleo-Pacific tectonic systems, the transition from the Neo-Tethyan to the Pacific tectonic systems, and the transition from the Paleo-Pacific to the Pacific tectonic systems. The tectonic transition of the East Asian OCCZ reflects the long-term mechanism of the Earth plate dynamic system driving the plate superconvergence in East Asia, in particular of the importance of the deep or submarine “Triple Poles”, the Southeast Asian U-shape subduction system, the Pacific LLSVP and the African LLSVP. More importantly, the Southeast Asian U-shape subduction system is also one of the important dynamic engines of the Earth plate motion.

Keywords

• ocean-continent connection zone
• paleo-tethyan ocean
• neo-tethyan ocean
• paleo-pacific ocean
• pacific ocean
• orogeny
• extension