南海南部新生代控盆断裂特征及盆地群成因

CENOZOIC BASIN-CONTROLLING FAULTS AND THEIR BEARING ON BASIN GROUPS FORMAION IN THE SOUTHERN SOUTH CHINA SEA

  • 摘要: 南海南部新生代盆地自北向南有南薇西、北康、礼乐、曾母、南沙海槽、文莱-沙巴、西北巴拉望等多个中小型新生代沉积盆地。这些盆地总体具有南断北超的箕状结构,靠近北部陆坡部位具有单一地堑结构,但是靠近南部具有两层结构,下部为箕状断陷,上部为叠瓦式逆冲推覆体。根据盆地不同演化阶段性质的转换和主控盆断裂特征,可将这些盆地归纳为3种盆地群:裂陷盆地群(南薇西、北康、礼乐)、裂陷-拉分-前陆叠合盆地(曾母)以及裂陷-前陆盆地群(南沙海槽、文莱-沙巴、西北巴拉望)。这些盆地的形成与盆缘一级控盆断裂带和盆内次级断裂密切相关。根据断裂的性质,一级控盆断裂带可分为张性、剪性、压性3种,包括南沙海槽北缘张性断裂带,南海西缘、卢帕尔和廷贾-李准等走滑断裂带和南沙海槽南缘逆冲断裂带。南海南部渐新世南海运动、中中新世南沙运动等构造事件不同程度地影响了这些盆地,表现在盆地由裂陷或拉分盆地转换为海相前陆盆地,断裂带不同程度的反转或由正断层转变为逆断层或走滑断层。盆地群的成盆动力学机制不同阶段是变化的,早期可能受欧亚大陆东南缘陆缘裂解作用、古南海的南向俯冲拖曳,导致南海南部裂离华南大陆并形成南断北超的箕状断陷盆地;晚期(16 Ma以后)南海南部出现指向北的前展式、叠瓦式逆冲推覆,其动力来源于南部的澳大利亚板块和欧亚板块的碰撞,同时导致盆地性质转换和婆罗洲地块的逆时针旋转。

     

    Abstract: There are many small and medium-sized Cenozoic sedimentary basins in the southern South China Sea, such as the Nanweixi Basin, the Beikang Basin, the Liyue Basin, the Zengmu Basin, the Nansha Trough, the Brunei-Sabah Basin, the Northwest Palawan Basin and other basins from north to south. In general, NE-trending faults control the formation of the half grabens with faulting in the north and overlapping in the south. However, single grabens are mainly developed in the northern continental slope, while two-layered basins developed in the south of the region, of which the lower layer is the graben and the upper layer the imbricated nappes. According to the nature of main controlling faults and the transition of the basins at different evolutionary stages, these basins can be divided into three groups:the rift basin group (the Nanweixi, Beikang and Liyue basins), the rift-pull-apart-foreland superimposed basin group (the Zengmu basin) and the rift-foreland basin group (the Nansha Trough, Brunei-Sabah, the Northwest Palawan basins). The formation of these basin groups is closely related to major marginal faults of the basins and secondary faults in the sub-basins. Based on the nature of the faults, the basin-controlling fault belts can be subdivided into three types:tensile, shear and compressional, including the extensional fault belt in the northern edge of the Nansha Trough, the strike-slip fault belts at the west edge of the Wanan Basin and the Lupar and the Tingjia-Lee Jun Fault belts, and the thrust fault belt in the southern edge of the Nansha Trough. Tectonic events which happened in southern South China Sea, such as the South China Sea Movement in Oligocene and the Nansha Movement in the Middle Miocene, affected the basins to various degrees. As the result, there was the inversion from a rift basin/pull-apart basin to a marine foreland basin, as well as the inversion of fault belts from normal faults to reverse faults or strike-slip faults. The kinetic mechanism of the basin groups varies in different stages. In the early stage, it may be related to the continental rifting of the southeast edge of the Eurasia continent, and the subduction and dragging of the Paleo-South China Sea slab resulted in the splitting of southern South China Sea from the South China continent, and then, half garbens formed with faulting in the north and overlapping in the south. In the later period (about 16 Ma), the north-directed imbricated thrust nappes propagated forward in the southern South China Sea due to the collision of the southern Australian Plate to the northern Eurasian Plate, which resulted in the transition of basin types and the counterclockwise rotation of the Borneo Block.

     

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