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The South China Sea Basin is one of the largest marginal basins in Asia. South China Sea is located to the east of Vietnam, west of Philippines and the Luzon Strait, and north of Borneo. Tectonically, it is surrounded by the Indochina Block on the west, Philippines Sea plate on the east, Yangtze Block to the north. A subduction boundary exists between the Philippines Sea Plate and the Asian Plate. The formation of the South China Sea Basin was closely related with the collision between the Indian Plate and Eurasian Plates. The collision thickened the continental crust and changed the elevation of the topography from the Himalayan orogenic zone to the South China Sea, especially around the Tibetan Plateau. The location of the South China Sea makes it a product of several tectonic events. All the plates around the South China Sea Basin underwent clockwise rotation, subduction and experienced an extrusion process from the early Cenozoic to the Late Miocene. The geological history can be classified into five tectonic evolutionary stages. (1) rift system development (2) sea floor spreading, (3) subsidence of the South China Sea, (4) closure of the South China Sea Basin and (5) uplift of Taiwan. == Rift system development == In the initial stage of the development of South China Sea, a basin was developed by extension to form two passive margins. The consensus is that the extension propagated from the northeast to the southwest, although some experts argue that the southwest basin is in fact older. The rifting and multiple grabens initiated around 55 Ma, based on seismic profiles across the southern China Shelf. The rifting intensified around 50 Ma due to the collision of the Indian and Eurasian plates. Two different models on how the extension initiated have been proposed, by Wang (2009) and by Cullen (2010). Wang's model for South China Sea rifting proposes a different area of rift development. The north and northeastern parts of the South China Sea formed their rifts earlier in the Paleocene. The south and southwestern parts of the South China Sea showed a later rifting around the Eocene or later. The difference in rifting and time gap between the northeastern and southwestern regions indicate the South China Sea is not a geologically homogeneous area, and its lithosphere could be divided into two areas, southwest and northeast according to its tectonic evolution. The reasons behind these differences in its rifting stage could be various, such as impact from different plates and different distribution of plumes under the crust. The Red River Fault along the western boundary of the South China Sea was believed to influence the rifting in the south and southwestern regions. Strike-slip faults. Cullen indicated that the South China Sea Basin's rifting could be traced back to the late Cretaceous and the extension concluded in two episodes during the Cenozoic. The first episode of extension occurred in the Early Paleocene and was widely distributed. The first rift system was located mainly in the Dangerous Ground (SE of South China Sea and in the Phu Khanh Basin, offshore central Vietnam. The slab pull between Philippines and South Asia is speculated to be the main force which drove the extension of the Dangerous Grounds and other parts of the South China Sea in that initial phase. The later episode of extension appeared from late Eocene to Early Miocene and propagated towards the southwest. During the second stage of extension the crust was thinned and finally experienced break-up.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tectonics of the South China Sea」の詳細全文を読む スポンサード リンク
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