Tectonic Property Of Proto-South China Sea

The South China Sea belongs to the marginal sea of the Western Pacific Ocean and has rich oil and gas resources.Since the Late Paleozoic,the South China Sea has been affected by the two major tectonic domains of the Tethys and the Pacific.The tectonic evolution has been restricted by the Eurasian plate,the Pacific plate,the Indian plate,the Australian plate,and the Philippines plate.The South China Sea has experienced the subduction and extinction of the Proto-South China Sea(PSCS)and the opening of the South China Sea,with a complex tectonic environment.The tectonic attributes and tectonic evolution of the Proto-South China Sea are crucial to understanding the Mesozoic and Cenozoic tectonic evolution of the South China Sea.At present,there are certain disputes about the existence time limit,tectonic attributes,subduction range and scale of the Proto-South China Sea.Sabah and Sarawak are closely related to the subduction and extinction of the Proto-South China Sea.Through the field survey data of Sabah and Sarawak and the analysis of rock geochemistry,isotope chronology and palaeomagnetism of field samples.Combining the regional geology,magmatic activity,paleontology and paleomagnetic data of the South China Sea and adjacent areas.The Proto-South China Sea was the Mesozoic oceanic crust that was once located south of South China and west of Indochina,where the present South China Sea is located.The Proto-South China Sea may have expanded during the late Late Cretaceous.Mainly draw the following points of understanding:1.The Sabah ophiolite set existed in the Early Triassic.The petrogeochemical characteristics of the basic rock of the ophiolite set show MORB characteristics.The paleomagnetic test(paleolatitude 29.9°S)indicates that the Triassic Sabah area may be located in the southern hemisphere.In the Jurassic,the Sabah area lacked sedimentary strata,and only some ophiolite sleeves existed,indicating that the Jurassic Sabah area may be in a deep-sea sedimentary environment.The paleo-geomagnetic test paleo-latitude of the Late Cretaceous gabbro sample in Telupid area of central Sabah is 10.6°N.The data shows that the paleo-latitude of Sabah area in the Late Cretaceous is higher than the present latitude.The minimum ages of detrital zircons from two sandstone samples in the Chert-Spilite(Cs)formations are 68±2Ma and 90±2Ma,respectively,and the minimum ages of detrital zircons from one sandstone sample in the Sapulut(SP)formations are 81±2Ma.The Cs formations sandstone detrital zircons are mostly precambrian and Cretaceous zircons.Comparing the tectonic evolution,geological characteristics and age maps of the detrital zircons in the neighboring areas of Sabah,it is speculated that the northern part of the South China Sea may be the main source area of the Cs formations sandstone,indicating that Sabah was once close to the northern part of the South China Sea.In the late Late Cretaceous,Sabah drifted southward and collaged with East Kalimantan,indirectly indicating that the Proto-South China Sea expanded in the late Late Cretaceous.2.The late Cretaceous granodiorite in the Lundu area in western Sarawak is a volcanic arc granite,and the paleo-latitude of the Lundu area in the Late Cretaceous is1.9°S through the analysis of paleomagnetic experiments.Mylonitic phyllite is exposed in the field outcrop of the Bukit Misin Line in northern Sarawak,and the tectonic lens is developed,showing the dynamic metamorphic rock produced by the subduction and extinction of the Proto-South China Sea.In the Tatau area of Sarawak,the Eocene Bawang Formation and the Oligocene Tatau Formation(?34Ma)are in angular unconformity contact.The Eocene Pelagus,Metah,Silantek,and Kapit Member formations have strong tectonic movement and weak regional metamorphism,which indirectly reflects the subduction and extinction of the Proto-South China Sea.3.Based on previous studies of the Proto-South China Sea,combined with the South China Sea and surrounding area geology,magmatic activity,paleomagnetic and paleontological data,it is believed that the Mesozoic and Cenozoic South China Sea is controlled by the two major tectonic domains of the Tethys and the Paleo-Pacific.The tectonic attributes of the Proto-South China Sea in different stages of the Early Triassic-Miocene are different.(1)During the Triassic period,the South China Sea was affected by both Paleo-Tethys and Paleo-Pacific.The Proto-South China Sea may be a remnant sea with paleo-Tethys oceanic crust or a part of the Paleo-Pacific.(2)In the Jurassic period,the South China Sea was affected by the superposition of the Middle Tethys and the Paleo-Pacific.The Proto-South China Sea may be a back-arc basin with a paleo-Pacific oceanic crust.(3)From the Early Cretaceous to the middle of the Late Cretaceous,the South China Sea was mainly affected by the Paleo-Pacific.The Proto-South China Sea may be a back-arc basin with Paleo-Pacific oceanic crust and gradually evolved into a semi-closed environment.(4)From the late Late Cretaceous to the Miocene,a semi-closed environment has been formed in the South China Sea.Based on the detrital zircons of the Cs Formation in Sabah,paleomagnetism,and the Semitau Mesozoic paleophyte evidence in the micro-block Semitau,it is inferred that the Proto-South China Sea oceanic crust may have expanded in the late Late Cretaceous.The Proto-South China Sea may be a marginal sea composed of new oceanic crust and remnant oceanic crust of the Paleo-Pacific Ocean.The subduction and extinction of the Proto-South China Sea thinned the crust in the northern part of the South China Sea,prompting the opening of the South China Sea,and the southwestern part of the Nansha Trough may be the remaining oceanic crust of the Proto-South China Sea.4.The South China Sea area developed the Proto-South China Sea Mesozoic strata,and the Late Mesozoic was affected by the subduction of the Paleo-Pacific plate.The northern and western basements of the South China Sea have experienced uneven uplift and weathering and erosion,while the southern part of the South China Sea has always received marine deposits.The northern and western basins of the South China Sea can strengthen the study of the Mesozoic new-born paleo-storage buried-hill oil and gas reservoirs.The Mesozoic in the southern basin of the South China Sea has the potential to develop buried-hill oil and gas reservoirs and paleozoic and new-storage lithological oil and gas reservoirs.