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

通过地质调查、砂质/泥质岩和绿岩的化学分析、煤化碎屑镜质组反射率的测定和重结晶白云母的K-Ar定年，阐明了三巴川带、岛岛带和赤部带之间的地质关系，以及三巴川带的折返过程。密马市南部的三巴川带和神山镇根据岩性和构造可分为北部和南部。Shosanji反形体位于北段的北缘，其轴线缓缓向东倾斜。砂砾岩片岩和泥质片岩的地球化学特征表明，北部和南部的母岩分别为北岛曼托带的KS-II单元(科尼阿西期-坎帕尼亚期)和KS-I单元(阿尔比期-早科尼阿希期)。这些结论表明，四国三百川带的大多数低品位变质岩为白垩纪Shimanto增生杂岩的底侵深部相。四国东部三百川带和北七道带泥质岩镜质组的表观最大反射率和最小反射率被测量。测量结果表明，镜质组具有光学双轴性。最大反射率和最小反射率的平坦度(Rmax-Rmin/Rmax)总体上向北增加，即向较低的结构层次增加。这将意味着增加埋藏深度或沉积深度。小津地区的赤布带可分为小津单元I/II和古屋单元UII。小津单元在结构上被古屋单元覆盖。古屋单元I和II可以分别与南部奇知武带的桑博山和藤野单元相对应。乌苏单元中变火山岩的砂岩地球化学和白云母K-Ar年龄表明，该单元相当于白垩纪岛曼托增生杂岩。

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.