Study of crustal-scale bending structures in island arcs

1.我研究了弯曲结构在侏罗纪米诺增生复杂的发展。主要研究地层是沿迷宫和Nagara河沿着的Kanayama单元、沿Ibi和Neo河沿着的Funabuseyama单元、北方古霍地区的Samondake单元和Yoro山脉的Kamiasou单元。研究结果表明：金山单元和船宿山单元的混杂岩主要是大洋板块俯冲作用的构造成因。提取包括地壳尺度弯曲在内的后期变形事件的影响，根据混杂岩组构分析，可以判断晚侏罗世至早白垩世板块的会聚方向，显示出左行斜向俯冲，Samondake单元由于地层绕近垂直轴旋转而具有不同尺度的弯曲构造。北西-南东向活动的八幡断裂位于区域性规模弯曲构造的枢纽区， ...更多信息 与日本西南弧走向几乎垂直的上阿苏单元整体南北向巨大弯曲，是由半波长> 10 km的西倾褶皱所引起的。这一巨大弯曲的成因尚不清楚，有待于进一步研究.通过对美浓地区加积单元泥质岩中伊利石结晶度的研究，评价了加积过程中和加积后的物理条件。IC值范围为高-中级成岩作用，但Samondake单元显示中级-低级成岩作用。这一结果表明，米诺带增生杂岩的古地热结构非常单一，没有受到后期变形事件的重新组合，其中，不连续逆冲推覆和大规模弯曲变形并不明显。为了进一步研究物理条件，我们成功地分析了赤石山四万十带石英脉中的流体包裹体。这种方法将在不久的将来应用于分析美浓增生杂岩的混杂岩的形成和沿着Itoigawa-Shizuoka构造线（ISTL）的断裂条件.本研究重新评价了赤石山脉基底岩石向北的弯曲与ISTL断裂系统之间的关系。对沿着ISTL韧性变形构造的精细组构分析表明，在绿片岩相变质条件下，断裂活动的初始阶段主要为左旋走滑。包括地震反射研究在内的地球物理研究表明，赤石山脉的弯曲基底和先存的ISTL断裂带沿沿着形成于旧ISTL以东的极低角度活动断裂系统逆冲到甲府盆地的第四纪沉积物上。少

1. I examined the bending structures developed in the Jurassic Mino accretionary complex. The main research strata are the Kanayama unit along the Maze and Nagara Rivers, the Funabuseyama unit along the Ibi and Neo Rivers, the Samondake unit in the northern Gujo area and the Kamiasou unit in the Yoro Mountains. The following results are clarified in this study.The melanges of the Kanayama and Funabuseyama units are mainly of tectonic origin due to subduction of oceanic plate. Extracting effects by the later deformation events, which include the crustal-scale bending, we can estimate the convergent direction of plate during the late Jurassic and the earliest Cretaceous on the basis of melange fabric analysis that shows sinistral oblique subduction.The Samondake unit have a various scale bending structures due to the stratal rotation about subvertical axis. The NW-SE trending active Hachiman fault is situated on the hinge area of regional scale bending structure, suggesting that the faul … More t was produced in association with the formation of bending structure, and is re-activated during the Quaternary.The overall N-S trending giant bend in the Kamiasou unit in the Yoro Mountains, that directed almost perpendicular to the trend of Southwest Japan arc, are due to the westward-plunging folds with half-wavelength of > 10km. The origin of this giant bend is still unknown, and further studies on this problem are required.2. Illite crystallinity (IC) of argillaceous rocks of the accretionary units in the Mino area has been studied to evaluate the physical condition during and after the accretion. The IC values range in higher to middle grade diagenesis except for the Samondake unit which shows middle to lower grade diagenesis. This result suggests that the paleo-geothermal structure of the accretionary complex in the Mino Belt is very monotonous and is not rearranged by the later deformation events which include out-of-sequence thrusting and giant-scale bending are not significant. For the next step to study physical conditions, we successfully analyzed fluid inclusions in quartz veins in the Shimanto Belt of the Akaishi Mountains. This method will be applied in near future to the analysis of melange formation of the Mino accretionary complex and to the faulting conditions along the Itoigawa-Shizuoka Tectonic Line (ISTL).3. The relationships between the northward bend of the basement rocks in the Akaishi Mountains and the ISTL fault system have been re-evaluated in this study. The precise fabric analyses of ductile deformation structures along the ISTL have revealed that the initial stage of faulting was mainly left-lateral strike slip under the condition of greenschist facies metamorphism. The geophysical researches including seismic reflection study suggest that the bended basement of the Akaishi Mountains and the pre-existing ISTL fault zone thrust onto the Quaternary sediments of the Kofu Basin along the very-low angle active fault system which were formed to the east of the older ISTL. Less