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Exhumation ofthe Sanlatgawa metamorphic belt from the viewpoint oftthe Shiananto accietionary complex

从夏南托演化杂岩看三拉嘎瓦变质带的剥露

基本信息

批准号：
17540437
负责人：
KIMINAMI Kazuo
金额：
$ 1.91万
依托单位：
Yamaguchi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2007
项目状态：
已结题

项目摘要

The followings have been performed to clarify geologic relationships among the Sanbagawa, Shimanto and Chichibu belts, and the process of exhumation of the Sanbagawa belt : geological survey, chemical analyses of psammitic/pelitic rocks and greenstones, measurements of vitrinite reflectance on coalified phytoclasts and K-Ar dating of recrystallized white mica The main results are as follows.1. The Sanbagawa Belt in the southern part of Mima City and Kamiyama Town can be divided into northern and southern parts on the basis of lithology and structure. The Shosanji antiform, of which axis plunges gently east, occurs northern margin of the northern part. Geochemistry of psammitic and pelitic schists suggests that the parents of the northern and southern parts are KS-II Unit (Coniacian-Campanian) and KS-I Unit (Albian-Early Coniacian)of the Northern Shimanto belt, respectively. These conclusions imply that most of the low-grade metasediments of the Sanbagawa belt in Shikoku are an underplated, deeper facies of the Cretaceous Shimanto accretionary complex.2. Apparent maximum and minimum reflectances have been measured on vitrinite in pelitic rock from the Sanbagawa and Northern Chichibu belts, in eastern Shikoku. The measurements have revealed that the vitrinites are optically biaxial. The flattening for maximum and minimum reflectances (Rmax-Rmin /Rmax)increases generally to the north, that is, to the lower structural level. This would imply an increase of burial depth or depth of accretion.3. The Chichibu belt in the Ozu area can be divided into Ozu unit I/II and Furuyabu unit UII. The Ozu unit is overlain structurally by the Furuyabu unit The Furuyabu unit I and II can be correlative to the Sambosan and Togano units in the Southern Chichibu belt, respectively. Sandstone geochemistry and K-Ar muscovite ages of metapelite in the Ozu Unit suggest that the unit is equivalent to the Cretaceous Shimanto accretionary complex.

为了阐明三波川带、四万十带和秩父带之间的地质关系以及三波川带的折返过程，进行了以下工作：地质调查、砂质岩/泥质岩和绿岩的化学分析、煤化植物碎屑镜质体反射率的测量以及再结晶白云母的K-Ar测年，主要结果如下： 1．三波川带位于美马市和神山町南部，根据岩性和构造可分为南北两部分。正山寺反形态的轴线平缓地向东倾斜，出现在北部的北缘。砂质片岩和泥质片岩的地球化学表明，北部和南部的母体分别是北四万十带的KS-II单元（康尼亚阶-坎帕阶）和KS-I单元（阿尔布阶-早康尼亚阶）。这些结论表明，四国三波川带的低品位变沉积岩大部分是白垩纪四万十增生杂岩的欠盘更深相。2．测量了四国东部三波川和秩父北部带泥质岩中镜质体的表观最大和最小反射率。测量表明镜质体是光学双轴的。最大和最小反射率（Rmax-Rmin /Rmax）的平坦度通常向北增加，即向较低的结构水平增加。这意味着埋藏深度或增生深度的增加。3．大洲地区的秩父带可分为大洲I/II单元和古薮单元UII。 Ozu 单元在结构上被 Furuyabu 单元覆盖。Furuyabu 单元 I 和 II 可以分别与南部秩父带的 Sambosan 和 Togano 单元相关。大洲单元中变泥岩的砂岩地球化学和 K-Ar 白云母年龄表明该单元相当于白垩纪四万十增生杂岩。