TECTONIC SUBDIVISION FOR THE PRE-TERTIARY ROCKS DISTRIBUTED IN NORTHEAST JAPAN

为重新认识日本东北部前第三纪岩石的构造划分，对其地层学、地质构造和地球化学进行了研究。调查的结果如下：分布于南北上带西缘的松田-摩台变质岩系为前志留纪基底之一，并非侏罗纪增生杂岩，其变质时间约为500 Ma.2。南北上构造带（+哈亚切纳构造带）与以侏罗系增生杂岩为主的邻近钻孔构造带的边界为高角度断裂，而非低角度断裂。对后侏罗世岩脉的捕虏体研究表明，南北上构造带和哈亚切纳构造带的古生代地层下部为变质基底和/或地壳基底，而非侏罗纪增生杂岩。因此，北上南带不是一个建立在侏罗纪增生杂岩之上的克利普。3 .再次确认了库祖马基—釜石带和阿卡—塔诺畑带侏罗系砂岩矿物和化学成分的差异。北上地块各带早白垩世花岗质岩石的N-MORB归一化模式和主元素化学特征无明显变化，具有岛弧和大陆弧的特征。根据这些事实，Nakagawa et al.（1989）对日本东北部的前第三纪沉积和变质岩采用了构造细分：从西部开始的Abukuma、South Kitakami、Hayachine构造、Kuzumaki-Kamaishi和Akka-Tanohata带。

For the purpose of reexamining the tectonic subdivision for the pre-Tertiary rocks distributed in Northeast Japan, stratigraphy, geologic structure and geochemistry of the rocks were studied. The results of the investigation are as follows:1. The Matsugadaira-Motai Metamorphic Rocks distributed in the western marginal part of the South Kitakami Belt is one of the pre-Silurian basements, not a Jurassic accretionary complex, which had been metamorphosed at ca. 500 Ma.2. The boundaries between the South Kitakami Belt (+ Hayachine Tectonic Belt) and the neigh boring tectonic belts, which are composed mainly of the Jurassic accretionary complexes, are high-angle faults, not low-angle ones. Studies on the xenoliths in the post-Jurassic dyke rocks suggest that the Paleozoic formations in the South Kitakami and Hayachine Tectonic Belts are underlain by the metamorphic and/or pultonic basements, not the Jurassic accretionary complexes. Therefore, the South Kitakami Belt is not a Klippe rests on the Jurassic accretionary complexes.3. The differences in the mineral and chemical compositions of the Jurassic sandstones of the Kuzumaki-Kamaishi and Akka-Tanohata Belts was reconfirmed.4. N-MORB normalized patterns and major element chemistry for early Cretaceous granitic rocks in all zones of the Kitakami Massif have no radical variation and are characteristic for island arc and continental arc types.From these facts the tectonic subdivision by Nakagawa et al. (1989) is adopted for pre- Tertiary sedimentary and metamorphic rocks in Northeast Japan: the Abukuma, South Kitakami , Hayachine Tectonic, Kuzumaki-Kamaishi and Akka-Tanohata Belts, from the west.