南海新生代的构造演化与沉积盆地

THE TECTONIC EVOLUTION AND SEDIMENTARY BASINS OF SOUTH CHINA SEA IN CENOZOIC

南海在新生代经历过复杂的构造演化史。中生代末至新生代早期,由于亚洲东南部燕山造山带岩石圈之拆沉作用,使下地壳及岩石圈上地幔向东南方向蠕动,在当时地表产生一系列北东向断裂,以及彼此分隔的地堑、半地堑。这次运动称做神狐运动。古新世一始新世时,这些地堑、半地堑接受了陆相沉积,它们构成南海诸沉积盆地的下构造层。在神狐运动期间,亚洲东南部岩石圈向东南方向蠕动,其西界是哀牢山-红河-莺歌海-南海西缘-万安大断裂,由于该断裂带的右旋走滑活动,沿该断裂带形成了莺歌海盆地和万安北盆地等走滑拉张盆地。始新世末,由于印度板块与欧亚板块发生了碰撞,在南海地区产生了向东南方向流动的上地幔流,从而引起了又一次构造运动——南海运动。南海运动的时间为始新世末至早渐新世。晚始新世时,南沙地块从中沙-西沙地块分离而向东南方向运动,早渐新世时与其南部的加里曼丹-西南巴拉望地块发生碰撞。在其后面发生了海底扩张而产生了南海西南次海盆。晚渐新世时,由于太平洋板块(菲律宾海板块)向亚洲东部俯冲的深度加深,阻挡了东亚上地幔向东南方向之流动,迫使其向南流动。在此地幔流作用下,礼乐-东北巴拉望地块由亚洲边缘分离而向南运动,早中新世与其南的加里曼丹-西南巴拉望地块发生了碰撞,在其后面由海底扩张而产生了南海中央次海盆。南沙地块与加里曼丹-西南巴拉望地块发生碰撞后,在其东南边缘由于岩石圈弯曲而产生了曾母盆地和文莱-沙巴盆地。在南海运动后,南海地区发生了热沉降和均衡沉降,普遍接受了晚渐新世-第四纪海陆交互相至海相沉积,组成了盆地的上构造层。南海地区新生代沉积盆地有四类:张裂盆地、走滑拉张盆地、前陆盆地和前弧盆地。这些盆地的发生与发展,和南海新生代的构造运动紧密相关。

The South China Sea had underwent a complicated tectonic evolution in Ceno- zoic .From end Mesozoic to early Cenozoic, due to the dellamination of the lower crust and the lithospheric upper mantle of Yanshan orogenic belt in southeastern Asia creeping southeast- wards, a series of northeast striking faults and separated grabens and halfgrabens were pro- duced on the earth surface within the time span of the Shenghu movement. Paleocene - Eocene terrigenous deposits, deposited in grabens and half-grabens, constituted the lower tectonic layer of the sedimentary basins of South China Sea.Throngh the period of Shenghu movement, the lithosphere of the southeast Asia crept southeastwards, it' s western margin of creeping belt is the dextral giant fault zone-the Ailao Shan-Red River-Yinggehai-the west margin of South China Sea-Wan' an fault zone.The strike-slip rifting basins, e.g.the Yinggehai and Wan'anbei basins were produced along this giant fault zone.In end Eocene, as the Indian plate colliding to the Asian plate and the upper mantle flowing southeastwards under the South China Sea area engendered Nanhai movement.The Nansha block was then broke apart from Xisha- Zhongsha block and moved southeastwards and collided with Kalimantan-southwest Palawan block. The seafloor spreading behind it resulted in Southwest Subbasin of South China Sea. In late Oligocen e, the subducting ocean lithosphere of the Pacific plate (Philippine Sea plate) had deepened and resisted the southeastwards Asian upper mantle flow, and therein forced Nansha Block flowing southwards.Along this mantle flow, the Liyue-northeast Palawan block separat- ed from the south margin of South China Continent and moved southwards and collided with Kalimantan-Southwest Palawan block in early Miocene, the Central Subbasin of South China Sea was then produced by seafloor spreading behind it. After the collision of the Nansha block and the Kalimantan-Southwest Palawan block, the Zengmu basin and the Brunei-Sabah basin were produced as the winding of the lithosphere of the southeast margin. After the Nanhai movement, the heat subsidence and isostatic subsidence happened in the South China Sea area, the continent-marine interactive and marine sediments of late Oligocene- Quaternary were deposited and consisted the upper tectonic layer. There have four kind of basins in the South China Sea area: rifting basin, strike-slip rifting basin, fore-land basin and fore-arc basin. The producing and the development of these basins closely relate with the tec- tonic movements in South China Sea.