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Study of crustal-scale bending structures in island arcs

岛弧地壳尺度弯曲结构研究

基本信息

批准号：
16540416
负责人：
KANO Ken-ichi
金额：
$ 2.11万
依托单位：
Shizuoka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-16540416/
关键词：
accretionary prism bending structure Mino Belt Shimanto Belt Itoigawa-Shizuoka Tectonic Line crust of island arc メガキンク

项目摘要

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

1.研究了侏罗纪米诺增生杂岩中发育的弯曲构造。主要研究地层是迷宫和长加拉河沿线的Kanayama单位、伊比河和Neo河流沿线的Funabuseyama单位、Gujo地区北部的Samondake单位和约罗山的Kamiasou单位。主要研究结果如下：Kanayama和Funabuseyama单元的混杂主要是洋板俯冲造成的构造成因。根据混杂组构分析显示的左倾斜俯冲作用，提取包括地壳尺度弯曲在内的后期变形事件的影响，可以估算出晚侏罗世和白垩纪早期板块的收敛方向。北西-南东向活动的哈奇曼断裂位于区域尺度弯曲构造的枢纽部位，表明福尔-…约罗山Kamiasou单元中的N-S向巨弯总体上与日本西南弧走向几乎垂直，是由于半波长约10公里的西倾褶皱所致。这一巨大弯曲的起源尚不清楚，还需要对这个问题进行进一步的研究。通过对米诺地区增生单元泥质岩的伊利石结晶度(IC)的研究，评价了增生过程中和之后的物理条件。除萨蒙达克单元显示中低级成岩作用外，其余成岩作用IC值均在高-中成岩作用范围内。这一结果表明，米诺带增生杂岩的古地热结构非常单调，不受后期变形事件的重新安排，包括无序逆冲和大规模弯曲等不显着。为了下一步研究物理条件，我们成功地分析了Akaishi山脉Shimanto带石英脉中的流体包裹体。该方法将在不久的将来应用于分析米诺增生杂岩混杂岩系的形成和Itoigawa-Shizuoka构造线(ISTL)的断裂条件。本文对Akaishi基岩北弯与ISTL断裂系统的关系进行了重新评价。对ISTL沿线韧性变形构造的精细组构分析表明，在绿片岩相变质作用的条件下，断裂活动的初始阶段以左旋走滑为主。包括地震反射研究在内的地球物理研究表明，Akaishi山脉的弯曲基底和先前存在的ISTL断裂带沿着在老ISTL以东形成的极低角度活动断裂系统推覆到科孚盆地的第四系沉积物上。较少