UPLIFT TECTONICS OF THE HIGH-PRESSURE SANBAGAWA METAMORPHIC BELT

高压三八川变质带隆起构造

基本信息

批准号：
03640644
负责人：
ISOZAKI Yukio
金额：
$ 1.22万
依托单位：
Yamaguchi university
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

项目摘要

Field survey and in-door works have been conducted in the 2 years research project, and following new results were obtained. 1) The Cretaceous Sanbagawa high-P/T metamorphic rocks occur tectonically above the weakly metamorphosed Late Cretaceous accretionary complex of the Shimanto belt in western, central and eastern Kii Peninsula, Southwest Japan. The boundary between them is a low-angle thrust which was recognized for the first time in Southwest Japan. 2) The Sanbagawa metamorphic rocks, on the contrary, tectonically underlie the weakly metamorphosed Jurassic accretionary complex of the Chichibu belt in central and eastern Shikoku. The boundary between them is a low-angle normal fault. These relations suggest that the Sanbagawa metamorphic rocks form a subhorizontal nappe, bounded from tectonically over-and under-lying units by low-angle faults. 3) Difference in metamorphic grades among these juxtaposed units forming a sandwich, indicates that the boundary faults represent remarkabl … More e pressure gap more than some kilobars. 4) The Sanbagawa belt in southwest Japan can be re-defined as an area of geotectonic window where the Sanbagawa metamorphic rocks are exposed by removal of tectonically overlying Jurassic accretionary complex. 5) The thickness of the Sanbagawa nappe is less than 2km, and this suggests its peculiar uplift tectonics from the metamorphic domain in the deeper part of subduction zone. 6) Judging from the timing of the Kula-Pacific ridge subduction, uplift of the Sanbagawa metamorphic rocks was led by wedge extrusion mechanism induced by ridge subduction along continental margin. These results are noteworthy because they not only renewed the total understanding of geotectonic history of Japan but also gave a new aspect in the study of orogeny, in particular, of the formation processes of the Cordilleran-type orogenic belts in general. Parts of the above-mentioned results were already presented orally and published in scientific articles elsewhere of this report. Less

历时两年的研究项目进行了野外调查和室内工作，取得了以下新成果：1）白垩纪三波川高变质岩产于四万十带弱变质的晚白垩世增生杂岩之上。位于日本西南部纪伊半岛的西部、中部和东部，它们之间的边界是日本西南部首次认识到的低角度逆冲断层。相反，变质岩在构造上位于四国中部和东部秩父带的弱变质侏罗纪增生杂岩之下，它们之间的边界是低角度正断层，这些关系表明三波川变质岩形成了近水平推覆体。以低角度断层为界的构造单元，3）这些并列的变质程度存在差异。单元形成三明治，表明边界断层代表了超过数千巴的显着压力间隙4）日本西南部的三波川带可以重新定义为三波川变质岩暴露的大地构造窗口区域。通过去除构造上覆盖的侏罗纪增生杂岩5）三波川推覆体的厚度小于2公里，这表明其独特的隆起构造。 6）从库拉-太平洋洋脊俯冲的时间来看，三八川变质岩的隆升是由洋脊沿大陆边缘俯冲引起的楔形挤压机制导致的。不仅刷新了对日本大地构造历史的全面认识，而且为造山运动研究，特别是科迪勒拉型造山带的形成过程提供了新的视角总体而言，上述结果的部分内容已在本报告的其他部分以口头方式提出并发表在科学文章中。