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

通过地质调查、砂泥质岩和绿岩的化学分析、煤化植物碎屑的镜质体反射率测定和重结晶白色云母的K-Ar定年，阐明了三坝川带、四万十带和秩父带之间的地质关系以及三坝川带的折返过程.米马市和神山町南部的三八川带根据岩性和构造可分为北方和南方。正山寺的反型，其轴线向东倾斜，出现在北方部分的北方边缘。砂质和泥质片岩的地球化学特征表明，北方和南方的母岩分别为北方四万十带的KS-Ⅱ单元（科尼亚期-坎帕期）和KS-Ⅰ单元（阿尔比期-早科尼亚期）。这些结论意味着四国三八川带的大多数低级变质沉积物是白垩纪四万十增生杂岩的底侵、深相。在四国东部的三宝川带和北方秩父带的泥质岩中测量了镜质体的表观最大和最小反射率。测量结果表明，镜质体是光学双轴的。最大和最小反射率（Rmax-Rmin /Rmax）的平坦化一般向北增加，即向较低的结构水平增加。这将意味着埋藏深度或加积深度的增加。小津地区秩父带可分为小津I/II单元和古矢部UII单元。Furuyabu单元I和II可分别与秩父带南部的Sambosan和Togano单元相对应。小津单元变质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。

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.