Provenance and dispersal patterns of sediments in the turbidite wedge of Nankai Trough
Provenance and dispersal patterns of sediments in the turbidite wedge of Nankai Trough
复制标题
南海海槽浊积楔沉积物物源及扩散规律
DOI：
10.2973/odp.proc.sr.131.105.1993
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
A. Taira
中科院分区：
文献类型：
--
作者：
M. Underwood;R. Orr;K. Pickering;A. Taira
在大洋钻探计划808号现场（第131航次）采集的岩心证明，南海海槽中部区域的海沟沉积物楔形体包括约600 m的半远洋泥、桑迪浊积岩和粉砂质浊积岩。地层序列向上变厚变粗，四国盆地的半远洋泥和火山灰层被粉砂和桑迪沟楔沉积物覆盖。过去对该地区粘土矿物学和砂岩岩学的调查得出了这样的假设：南海海槽的大部分碎屑来自伊豆-本州碰撞带，并通过轴向浊流向西南输送。另一方面，船上对古水流指标的分析表明，外边缘沟楔相的粉砂质浊积岩中的大多数涟漪交叉纹层向北和西北倾斜;因此，许多浊流反射出了沟的向海斜坡，而不是沿沟轴直线向下移动。基于海岸的碎屑粘土矿物分析表明，半远洋泥和基质材料内的桑迪和粉砂质浊积岩都富含伊利石;伊利石是第二个最丰富的粘土矿物，其次是蒙皂石。在一般情况下，相对矿物百分比变化相对较小的深度函数，和半远洋粘土矿物人口几乎是相同的浊积岩基质人口。不同粒级（<2 μm和2-6 μm）之间的比较表明，矿物分配量适中，粗粒级中蒙脱石含量增加，细粒级中蒙脱石含量增加。伊利石结晶度指数值与源区晚期近变质作用和浅变质作用条件一致。检测到的三种云母多型，2 MJ品种占主导地位的IM和IMD多型，这些数据是一致的伊利石结晶度值。云母B o晶格间距的测量表明，碎屑伊利石颗粒是从中压变质带剥蚀而来的。总的来说，这些数据与伊豆-本州碰撞带的岩性和变质特征非常吻合。因此，第131航次的资料证实了碎屑物源的较早出现。沉积物扩散的区域格局主要是由西南方向的轴向浊流，轴向流的径向扩张，悬浮云的斜向运动到和超出南开海槽的向海斜坡，和流反射回沟轴的组合。
Drill core recovered at Ocean Drilling Program Site 808 (Leg 131) proves that the wedge of trench sediment within the central region of the Nankai Trough comprises approximately 600 m of hemipelagic mud, sandy turbidites, and silty turbidites. The stratigraphic succession thickens and coarsens upward, with hemipelagic muds and volcanic-ash layers of the Shikoku Basin overlain by silty and sandy trench-wedge deposits. Past investigations of clay mineralogy and sand petrography within this region have led to the hypothesis that most of the detritus in the Nankai Trough was derived from the Izu-Honshu collision zone and transported southwestward via axial turbidity currents. Shipboard analyses of paleocurrent indicators, on the other hand, show that most of the ripple cross-laminae within silty turbidites of the outer marginal trench-wedge facies are inclined to the north and northwest; thus, many of the turbidity currents reflected off the seaward slope of the trench rather than moving straight down the trench axis. Shore-based analyses of detrital clay minerals demonstrate that the hemipelagic muds and matrix materials within sandy and silty turbidites are all enriched in illite; chlorite is the second-most abundant clay mineral, followed by smectite. In general, the relative mineral percentages change relatively little as a function of depth, and the hemipelagic clay-mineral population is virtually identical to the turbidite-matrix population. Comparisons between different size fractions (<2 μm and 2-6 μm) show modest amounts of mineral partitioning, with chlorite content increasing in the coarser fraction and smectite increasing in the finer fraction. Values of illite crystallinity index are consistent with conditions of advanced anchimetamoΦhism and epimetamoΦhism within the source region. Of the three mica poly types detected, the 2Mj variety dominates over the IM and IMd polytypes; these data are consistent with values of illite crystallinity. Measurements of mica b o lattice spacing show that the detrital illite particles were eroded from a zone of intermediate-pressure metamoΦhism. Collectively, these data provide an excellent match with the lithologic and metamoΦhic character of the Izu-Honshu collision zone. Data from Leg 131, therefore, confirm the earlier inteΦetations of detrital provenance. The regional pattern of sediment dispersal is dominated by a combination of southwest-directed axial turbidity currents, radial expansion of the axial flows, oblique movement of suspended clouds onto and beyond the seaward slope of the Nankai Trough, and flow reflection back toward the trench axis.