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During the Mesozoic era, the South China Sea and its environs were located at the south-eastern margin of the Eurasian continent. There has been hot debate on the influences of Tethyan and Paleo-Pacific tectonics to the Mesozoic evolution of the area. This paper compiles lithofacies maps of six time slices and discusses the paleogeographic and tectonic evolution of the area based on this compilation and other data on structural deformation and magmatism. In the Early Triassic, the Paleotethys Ocean extended eastward to the study area through the Song Da passage. Then a significant east-west differential evolution began. In the Late Triassic, the western area uplifted as a result of the collision between the Indosinian and South China blocks during the Indosinian orogeny, and the Song Da passage has closed since then. Meanwhile, a transgression of Paleo-Pacific waters occurred in the eastern and south-eastern portions of the area, forming the 'East Guangdong-North-west Borneo Sea'. In the Early Jurassic, seawater transgression was even more pronounced, resulting into the connection of this sea with the Mesotethys Ocean to the west. Large quantities of Tethyan water carrying Tethyan organisms entered the area. In the Middle Jurassic, a short-lived transgression occurred in the eastern Mesotethys and resulted in the formation of the 'Yunnan-Burma Sea'. The Late Jurassic to Early Cretaceous was the climax of the subduction of both the Mesotethys and PaleoPacific towards the Eurasian continent. This led to the formation of the great 'Circum South-east Asia Subduction-Accretion Zone' in the Middle or Late Cretaceous. This paper also presents various lines of evidence for a newly recognized segment of this Mesozoic subduction-accretion zone buried under Cenozoic sediments in the north-eastern South China Sea.The deep-sea basin of the South China Sea (SCS) was formed by seafloor spreading in the Late Oligocene to Early Miocene (Holloway 1982;Taylor & Hayes 1983;Briais et al. 1993). The shelves and slopes of the SCS are floored mainly by Cenozoic sediments. While great attention has been paid to the geology and evolution of the SCS and its Cenozoic sedimentary basins, there has been little study on the pre-Cenozoic geology and evolution of the area. This has changed recently, stimulated by the urgent demand to know the pre-Cenozoic hydrocarbon potential of the region (e.g. Su et al.

A segment of Mesozoic subduction-accretion zone was inferred across the northeastern South China Sea at approximately NE45° orientation. Basic evidence includes the following: A belt of peek gross horizontal Bouguer gravity gradient (PGHGBA) is comparable in size and intensity to that of the Manila subduction-accretion zone. A belt of high positive magnetic anomalies appears to the north and sub-parallel to the PGHGBA, representing the volcanic arc associated to the subduction zone. The PGHGBA crosses obliquely both Cenozoic structures and present seafloor topography, indicating a pre-Cenozoic age. The segment is offset left-laterally by NW-running strike-slip faults, in concord with the Mesozoic stress field of South China. In addition, the existence of the subduction zone is supported by wide-angle seismic data obtained in different years by different institutions. At approximate localities, a north-dipping ramp of Moho surface is indicated by records of ocean-bottom seismometers, and a strong reflector about 8 km beneath the Moho reflector is indicated by both OBS and long-cable seismic records. The identification of a segment of Mesozoic subduction zone in NE South China Sea fills nicely the gap of the Great Late Mesozoic Circum SE Asia Subduction-acrretion Zone, which extended from Sumatra, Java, SE Kalimantan to N Palawan, and from Taiwan, Ryukyu to SW Japan.

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