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

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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.