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东沙群岛及其邻近海区 (简称东沙海区 )位于南海北部大陆边缘 ,东邻马尼拉俯冲构造带。为了讨论晚新生代以来东沙海区的构造变形特征 ,从中找出吕宋弧对中国东南大陆边缘碰撞的构造相关 ,特别是 8Ma以来的吕宋岛弧和中国大陆边缘之间构造消减过程的响应。根据地震地层学分析 ,结合区域重磁资料、ODP1 84钻孔资料对东沙群岛海区晚新生代构造特征进行了分析。东沙海区自南海扩张后发育了 3个沉积层序 (层序Ⅴ ,Ⅵ ,Ⅶ ) ,经历了较强烈的构造抬升作用、岩浆活动、沉积物剥蚀。该区发育NEE SWW和NW SE向两组断裂 ,且以NEE SWW向断裂最为发育。断裂大多具有多次活动 ,且为上新世到第四纪的活动断裂构造 ,断块抬升幅度大 ,沿断裂带发生岩浆侵入。分析结果表明 ,晚新生代期间经历了二次重要的构造运动 ,即东沙运动 ( 9 8— 4 4Ma)和流花运动 ( 1 89— 1 4Ma) ,奠定了该区的构造格局。综合该区东强西弱构造变形、构造抬升发生的时间和应力场变化等特征看 ,该区受 8Ma以来中国东部大陆边缘与吕宋岛弧碰撞所产生的构造运动的影响 ,在 8Ma以前 ,由于台湾岛不存在 ,活动的古东海大陆边缘延伸至东沙群岛海区东北部。
Dongsha Islands and its adjacent sea area (referred to as the East Sea area) is located in the northern margin of the South China Sea continental margin, Manila subduction tectonic belt to the east. In order to discuss the tectonic deformation characteristics of the Dongsha sea area since the Late Cenozoic, the tectonic correlation of the Luzon arc to the marginal collisions in southeastern China was found out, especially the response to the tectonic depletion process between the Luzon arc and the margin of China since 8Ma. According to the analysis of seismic stratigraphy, combined with the regional gravity and magnetic data, ODP1 84 drilling data, the structural characteristics of the Late Cenozoic in the Dongsha Islands sea area are analyzed. Three sedimentary sequences (sequences Ⅴ, Ⅵ and Ⅶ) developed in the Dongshahai Sea since the expansion of the South China Sea experienced strong tectonic uplift, magmatism and sediment erosion. In this area, NEE SWW and NW SE developed to two groups of faults, and the most developed faults were NEE SWW. Most faults have multiple activities and are active faults from the Pliocene to the Quaternary. The faults are uplifted greatly and the magma intrudes along the fault. The analysis results show that during the Late Cenozoic, two important tectonic movements, namely the Dongsha movement (9 8- 4 4 Ma) and the Liuhua movement (1 89-1 4 Ma), have been completed, which established the tectonic framework of this area. Based on the characteristics of the structural deformation of eastern weakening and weakening of eastern Qiangxiang, the time of tectonic uplifting and the change of stress field, the tectonic movement occurred from the collision between the eastern continental margin of China and Luzon Island since 8Ma. Before 8Ma, Due to the absence of Taiwan Island, the active continental margin of the ancient East China Sea extends to the northeast of the Dongsha Islands.