Structural setting of the Leg 156 area, northern Barbados Ridge acretionary prism
Structural setting of the Leg 156 area, northern Barbados Ridge acretionary prism
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巴巴多斯海岭北部156腿区域的结构背景
DOI：
10.2973/odp.proc.ir.156.102.1995
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
J. Moore
中科院分区：
文献类型：
--
作者：
G. Moore;Z. Zhao;T. Shipley;N. Bangs;J. Moore
Leg 156区域的结构框架由区域二维地震反射线、多波束测深和三维地震数据集提供，该数据集对巴巴多斯增生棱柱下坡125公里区域下方的结构进行成像。棱镜是由海洋板块沉积物形成的，这些沉积物在斜坡的脚趾处被刮掉并堆积到上面的板块上。棱柱从逆冲锋处的约200 m增厚到逆冲锋向陆地75 km处的至少4.5 km。区域滑脱将增生棱柱与俯冲洋壳上携带的逆冲沉积物分开。洋壳被偏移量高达 250-300 m 的正断层切割。由此产生的地垒和地堑地形的波长为 1-3 公里，趋势为东北偏东。逆冲锋向海的地层被许多正断层折叠和切割。上部200 m的海洋板块沉积物在逆冲锋处增生，其余沉积部分在棱柱下方逆冲。逆冲沉积物的厚度通常约为 500 m，但根据底层基底地形，厚度也可能小至 200 m。吸积棱柱被无数的逆冲和逆冲切割。棱柱趾部附近的逆冲走向为西北偏北，间距为100至750 m。逆冲断层的方向与汇聚方向（~东西向）或底层基底地形的趋势无关。无序逆冲呈东北偏东走向，主导着逆冲锋向陆地约 5-8 公里、宽 5 公里的区域的表面结构。可以通过三维数据体在水平切片中横向追踪各个推力。横向坡道在交叉线上很容易识别。所有的推力都集中在肩部。滑脱通常位于共同地层层位附近，但在地层折叠或断层处局部向上或向下切割。脱脱通常被成像为简单的反相反射，其被建模为约 10-14 m 厚的低速、高孔隙率区域。我们推断，这个薄的高孔隙率区域是一个欠压实的高流体压力部分，并且绘制的滑脱幅度和极性的变化反映了滑脱流体含量和流体运移路径。
The structural framework of the Leg 156 area is provided by a regional two-dimensional seismic reflection line, multibeam bathymetry, and a three-dimensional seismic data set that images the structure beneath a 125-km area of the lower slope of the Barbados accretionary prism. The prism is formed of oceanic plate sediments that are off scraped at the toe of the slope and accreted to the overriding plate. The prism thickens from about 200 m at the thrust front to at least 4.5 km at a distance 75 km landward of the thrust front. A regional décollement separates the accretionary prism from underthrust sediments carried on the subducting oceanic crust. The oceanic crust is cut by normal faults with offsets as great as 250-300 m. The resulting horst and graben topography has a wavelength of 1-3 km and trends east-northeast. Strata seaward of the thrust front are folded and cut by numerous normal faults. The upper 200 m of oceanic plate sediment is accreted at the thrust front, and the remaining sedimentary section is underthrust beneath the prism. The thickness of underthrust sediment is usually about 500 m, but can be as little as 200 m depending on the underlying basement topography. The accretionary prism is cut by numerous thrusts and back thrusts. Thrusts near the toe of the prism trend north-northwest with spacing of 100 to 750 m. The orientation of the thrusts does not correlate with either the convergence direction (~east-west) or the trend of underlying basement topography. Out-of-sequence thrusts trend east-northeast and dominate the surface structure of a 5-km-wide zone approximately 5-8 km landward of the thrust front. Individual thrusts can be traced laterally in horizontal slices through the three dimensional data volume. Lateral ramps are easily recognized in cross lines. All thrusts sole out on the décollement. The décollement is typically located near a common stratigraphic horizon, but locally cuts upor downsection where the stratigraphy is folded or faulted. The décollement generally is imaged as a simple reversed-phase reflection that has been modeled as a low-velocity, high-porosity zone about 10-14 m thick. We infer that this thin, high-porosity zone is an undercompacted, high-fluid-pressure section, and that mapped variations in décollement amplitude and polarity reflect décollement fluid content and fluid migration paths.