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

近年来，对海沟和弧前地质过程的详细研究对于了解大陆的地壳演化变得越来越重要。对岛曼托带陆域的地质和古生物研究表明，其起源于与俯冲有关的增生过程。然而，到目前为止，揭示主要冲断带构造特征的构造研究还很少，从构造地质学的角度对室户半岛和哈塔半岛的上岛曼托超群进行了研究。结果表明，上什曼托构造带的增生杂岩具有大型逆冲带的构造特征，即多层叠断层、复式构造和叠瓦状构造。不同类型和样式的褶皱基本上提供了单一逆冲断层中的褶皱实例。四国上岛曼托超群在结构上被划分为连贯的单位a…更多和混血单元。该相干单元的特征是由弱变形的砂岩和泥岩交替层组成的浊积序列。它被细分为剥离的增生杂岩和其上覆的斜坡沉积两个单元。混杂岩系的混合过程可视为吸积棱柱浅层重力滑动大量堆积的结果，也可看作是吸积棱柱深层底侵过程的结果。斜坡型砂岩密度低，纵波速度低，密度高。混杂单元中的砂岩块具有介于增生杂岩单元和斜坡沉积单元之间的物性。相反，混杂岩单元砂岩的杨氏模数远高于前两个单元。三轴压缩试验表明，在大于50 MPaC.P.的条件下，斜坡型砂岩的变形方式转变为韧性流动的变形方式，而在超过200 MPaC.P.的条件下，增生砂岩的变形方式仍为脆性破坏，混杂砂岩的块体中存在两种结构类型。一种是以“网状结构”为特征的碎裂变形，另一种是由液化作用与周围泥质基质混合形成的软沉积物变形。从物理力学性质上看，中新世混杂岩单元可视为斜坡盆地中变形的滑坡体，其中既有来自增生基底的砂岩块，也有来自斜坡沉积本身的砂岩块。较少

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