27. SEDIMENTARY FACIES EVOLUTION OF THE NANKAI FOREARC AND ITS IMPLICATIONS FOR THE GROWTH OF THE SHIMANTO ACCRETIONARY PRISM1
27. SEDIMENTARY FACIES EVOLUTION OF THE NANKAI FOREARC AND ITS IMPLICATIONS FOR THE GROWTH OF THE SHIMANTO ACCRETIONARY PRISM1
复制标题
27 南海前弧沉积相演化及其对四万十增生棱柱生长的影响1
DOI：
--
复制
发表时间：
1993
期刊：
影响因子：
--
通讯作者：
Nankai Trough
中科院分区：
文献类型：
--
作者：
A. Taira;J. Ashi;Nankai Trough
深海钻探计划-大洋钻探计划的钻探结果与四国盆地、南海海槽和南海向陆斜坡区的现场调查数据相结合，为研究碎屑岩为主的增生前弧的沉积相演化提供了一个独特的机会。在这里，我们认为相演化模型的基础上，钻井结果，IZANAGI侧扫图像，地震反射剖面。本文提出的南海弧前盆地沉积相模式由两部分组成：洋底-海沟-下斜坡沉积相演化和上斜坡-弧前盆地沉积相演化。前者开始于基底远洋和半远洋泥岩，其上覆有变粗的海沟浊积岩向上序列，后者依次被斜坡裙部滑塌和较低斜坡半远洋泥岩覆盖。这一组合是逐步断裂和折叠成一个巩固的增生棱柱，然后断裂和断裂的上斜坡区。上斜坡区域海底的大规模破坏产生了包含分散在泥浆基质中的较老的增生棱柱体所形成的石化块体的滑塌堆积物。较老的增生棱柱体与上斜坡滑塌堆积体之间的接触面是海底不整合面，这是较老的棱柱体折返至海底的第一个地层学证据。然后，滑塌层被弧前盆地平原泥岩和浊积岩覆盖，这些泥岩和浊积岩逐渐被向上变粗的三角洲-陆棚层序覆盖。为了验证弧前相模式的可行性，尝试将弧前相模式应用于四万十带。该模型可以解释在四万十带中观察到的几种特征性岩性。在四万十带发现的不整合面进行了评估，以提供一个估计的棱柱体的折返率。与独立测量的折返速率相比，得出0.5至1公里/百万年。棱镜的垂直生长。
A combination of Deep Sea Drilling Project-Ocean Drilling Program drilling results and site survey data in the Shikoku Basin, Nankai Trough, and Nankai landward slope region provides a unique opportunity to investigate the sedimentary facies evolution in the clastic-dominated accretionary forearc. Here, we consider the facies evolution model based on the drilling results, IZANAGI sidescan images, and seismic reflection profiles. The sedimentary facies model of the Nankai forearc proposed in this paper is composed of two parts: the ocean floor-trenchlower slope sedimentary facies evolution and the upper slope to forearc basin sedimentary facies evolution. The former begins with basal pelagic and hemipelagic mudstones overlain by a coarsening upward sequence of trench turbidites which are, in turn, covered by slope apron slumps and lower slope hemipelagic mudstone. This assemblage is progressively faulted and folded into a consolidated accretionary prism that is then fractured and faulted in the upper slope region. Massive failure of the seafloor in the upper slope region produces olistostrome deposits that contain lithified blocks derived from older accretionary prism dispersed in a mud matrix. The contact between the older accretionary prism and the upper slope olistostrome is a submarine unconformity that is the first stratigraphic evidence for the exhumation of an older prism to the seafloor. The olistostrome beds are then overlain by forearc basin-plain mudstone and turbidites which are progressively covered by coarsening-upward delta-shelf sequences. An application of the forearc facies model to the Shimanto Belt was attempted in order to ensure feasibility of this model. Several characteristic lithologies observed in the Shimanto Belt can be interpreted with this model. The unconformities found in the Shimanto Belt were evaluated to provide an estimate for the exhumation rate of the prism. Comparison with independent measurement of exhumation rate provides a 0.5 to 1 km/m.y. vertical growth of the prism.