付加体の構造地質学 : 四万十帯を中心とした研究の現状と課題  [in Japanese] Structural geology of accretionary complexes : Recent progress and future perspectives mainly based on the studies of the Shimanto Belt, Southwest Japan  [in Japanese]

最近の付加体研究の動向を, 主として四万十帯での構造地質学的研究に基づいてレビューした。最近におけるデュープレックス構造の認識は, 浅部でのはぎ取り付加と深部での底付け付加とが組み合わって付加作用が進行することを明らかにした。付加ユニットはout-of-sequence thrustによって再配置され, その内部の褶曲は層平行剪断を伴うfault-related foldingによって形成されている。付加体内には様々な起源のメランジュが発達し, 付加体形成に重要な役割を果たしている。付加体構成層の変形メカニズムは, 含水堆積物の脱水・同化過程に依拠している。新しい手段による続成-弱変成度の検討は, 付加体の造構過程の解析にあらたな視点を提供した。

Recent progress and future perspectives of studies of accretionary complexes were reviewed on the basis of data from the field of analytical structural geology in ancient accretionary terranes. The studies of Cretaceous-lower Miocene Shimanto Belt of Southwest Japan have greatly contributed to the development of structural geology of accretionary terranes, which are palticularly high lighted here. The recognition of duplex structures revised an accretion process of convergent margin from the classical and simple offscraping model to the combined model of offscraping accretion in the upper tectonic level and underplating of underthrust sequence in the lower one. Out-of-sequence thrustings within the accreted body are fundamental process for rear-rangement of the tectono-stratigraphic units. Folds in the units may be generated mainly by fault-related foldings accompanied with layer-parallel shear along thrusts. Wide occurrences of melanges of different origins have suggested that the melanges are essential units of accretionary complexes and may play an important role for the material circulations of convergent margins. Zones of thick tectonic melanges were presumably produced by layer- parallel shear along decollements in subduction zones, The deformation mechanisms of accreted materials mainly depend on dewatering and lithification process from water-saturated sediments to consolidated metamorphic rocks. Studies of diagenesis and low-grade metamorphism have been advanced by using vitrinite reflectance, illite crystallinity, fission-track thermochlonology and so on. These data have provided new in sights of discussions on structural processes which include burial, exhumation and erosion of accretionary complexes.