Physical and Mechanical Properties of the Tertiary Sedimentary Rocks in the Shimanto Belt in Shikoku.

近年来，深入研究海沟和弧前地质过程对认识大陆地壳演化具有重要意义。石曼托带陆域的地质和古生物研究表明，其成因是俯冲相关的增生过程。然而，到目前为止，揭示主要冲断带预期结构特征的构造研究还不多。从构造地质的角度研究了武户半岛和羽田半岛的上岛户超群。结果表明，上石曼托带增生杂岩的构造特征具有大冲断带的构造特征，主要表现为多叠断、复式和叠瓦构造。各种类型和样式的褶皱基本上提供了单个逆冲片上褶皱的例子。四国上岛东超群在构造上可分为相贯单元和混杂单元。相干单元的特征是一个弱变形、砂岩和泥岩交替层的浊积层序。它被细分为两个单元的剥落增生杂岩和其上的斜坡沉积物。混合岩的混合过程可以看作是在吸积棱镜的浅层或在吸积棱镜的深层的底沉积过程中重力滑动的大量积累的结果。对这些单元的砂岩进行了物理力学性质的考察。与增生杂岩相比，斜坡沉积物的砂岩密度较低，纵波速度较低，孔隙度较高。而混杂岩单元中的砂岩块体的物性值介于增生杂岩和斜坡沉积单元之间。相反，混杂岩单元中砂岩的杨氏模量远高于前两个单元。三轴压缩试验表明，在50MPa C.P.以上的现场，边坡砂岩的变形模式转变为韧性流动的变形模式，而在200MPa C.P.以上的现场，增生砂岩的变形模式仍然是脆性破坏。一种是碎裂变形，其特征为“网状结构”；另一种是软沉积变形，其成因是与周围泥质基质液化混合。中新世混色岩单元的物理力学性质可以看作是斜坡盆地内的变形鲕粒层，其中既有来自于吸积基底的砂岩块体，也有斜坡沉积物本身的砂岩块体。少

In recent years, detailed study of trench and forearc geologic processes have become increasingly important to understand the crustal evolution of continents. Geological and paleontological investigations of the onland area in the Shimanto Belt have demonstrated its origin of subduction-related accretionary process. However, not much structural studies that disclose structural features anticipated in a major thrust belt have been done until the present.The Upper Shimanto Supergroup in the Muroto Peninsula and the Hata Peninsula has been studied on the point of the structural geology. As a result, it is revealed that the structural features of accretionary complex in the Upper Shimanto Belt is characterized by that of the large thrust belt, such as multi-stacking faults, duplex and imbricated structures. Various classes and styles of folds basically provide example of folds in a single thrust sheet.The Upper Shimanto Supergroup in Shikoku is structurally divided into the coherent unit a … More nd the melange unit. The coherent unit is characterized by a turbidite sequence of weakly deformed, alternated beds of sandstone and mudstone. It is subdivided into two units of the offscraped accretionary complex and the slope sediments overlying on it. The mixing process of the melange can be regarded as the result of large accumulations of gravitational slides in the shallow level of the accretionary prism or at the underplating process in the deeper levels of the accretionary prism.Sandstones of these units are examined on the point of the physical and mechanical properties. The sandstones of the slope sediments have lower densities, lower P-wave velocities and higher prosities than those the accretionary complex. While sandstone blocks in the melange unit have physical values between those of the accretionary complex and slope sediment units. On the contrary, Young's modulus of sandstone in the melange unit is well higher than previous two units. The triaxial compression test indicates that the deformational mode of the slope sandstones changes to the those of ductile flow in the field more than 50MPa C.P., whereas those of the accretionary sandstone is still brittle failure in the field more than 200MPa C.P. Two types of texture are differentiated in the blocks of the melange sandstone. One is the cataclastic deformation characterized by the "web structure" and the other is the soft sediment deformation which was caused by the liquefaction and mixing with a surrounding pelitic matrix. Viewed in the light of physical and mechanical properties, the Miocene melange unit can be regarded as the deformed olistostrome in the slope basin which contains sandstone blocks derived from both the accretionary basement and the slope sediments itself. Less