Tectonique d'accrétion dans les îles du Japon et évolution de la croûte continentale

Revised interpretation of the basement geology of the Japanese island arcs which has emerged in the last 20 years or so, indicates that they are mostly composed of two geological belts: volcanics (greenstone)-granitoid belt (VGB) and turbidite-granitoid belt (TGB). The VGB exhibits thrust-bounded thick sequences of basic volcanics and associated granitoid plutons and was formed by arc-arc collision process. The TGB is composed of turbidite and melange units and was formed by progressive growth of trench accretionary prism and later intrusion of granitoid. Both belts represent a style of crustal growth in a convergent margin. In these orogenic belt, involvement of many oceanic island arcs and formation of the VGB were a major mechanism of juvenile crust, in addition to the continental crust. The formation of the TGB played a major role in the reworking and recycling of the continental crust which resulted in a long-term secular compositional change of the upper crust.