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Crustal structure and variation in the southwest continental margin of the South China Sea: evidence from a wide-angle seismic profile
Journal of Asian Earth Sciences ( IF 3 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.jseaes.2020.104557
Xiaodong Wei , Aiguo Ruan , Weiwei Ding , Zhaocai Wu , Chongzhi Dong , Yanghui Zhao , Xiongwei Niu , Jie Zhang , Chunyang Wang

Abstract A 680-km long wide-angle seismic profile was acquired in the southwest continental margin (SWCM) of the South China Sea to better understand its crustal variation and continental extension. By using two-dimensional forward ray-tracing, and joint refraction and reflection travel time inversion methods, velocity structures of the SWCM are yielded. The model results show a hyper-stretched continental crust with a thickness of 10–18 km, which is variable under sedimentary basins and reef areas. Compared with βwc, βuc, and βlc derived from the crustal thickness, the degree of the whole crust extension appears to be larger than that of the upper crust but lower than that of the lower crust, except for the model of 560–610 km. Thus, we infer that depth-dependent extension of the crust has occurred in the SWCM. High velocity bodies with velocities larger than 7.0 km/s are sporadically distributed in the lower crust, which might be related to the remnant Mesozoic arc that can be attributed to the subduction of the paleo-Pacific plate. The obvious low velocity anomaly with the maximum thinning crust below the boundaries of the Nansha Trough and Palawan-Borneo thrust wedge (PBTW) is interpreted as the frontal thrust of the PBTW.

中文翻译:

南海西南陆缘地壳结构与变化:来自广角地震剖面的证据

摘要 在南海西南大陆边缘(SWCM)获得了680 km长的广角地震剖面,以更好地了解其地壳变化和大陆伸展。利用二维前向射线追踪、联合折射和反射走时反演方法,得到SWCM的速度结构。模型结果显示厚度为 10-18 公里的超拉伸大陆地壳,在沉积盆地和礁区下是可变的。与由地壳厚度推导出的βwc、βuc、βlc相比,除了560-610km的模型外,整个地壳的伸展程度似乎大于上地壳但小于下地壳。因此,我们推断 SWCM 中发生了与深度相关的地壳伸展。速度大于 7.0 km/s 的高速体在下地壳中零星分布,这可能与古太平洋板块俯冲残余中生代弧有关。南沙海槽和巴拉望-婆罗洲逆冲断楔(PBTW)边界以下地壳最大减薄的明显低速异常被解释为PBTW的正面逆冲。
更新日期:2020-11-01
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