CRETACEOUS TO HOLOCENE FORE-ARC EVOLUTION IN JAPAN AND ITS IMPLICATION TO CRUSTAL DYNAMICS

The forearc tectonic evolution of Japan since Cretaceous time has revealed three important tectonic processes: the formation of a sedimentary accretionary prism, crustal accretion and imbrication, and subduction erosion. The accretion of sediments seems to have been controlled mainly by the input of sediment into a trench, as has been documented in the Shimanto Belt and the Nankai accretionary prism. Crustal accretion and imbrication have been taking place at a collision zone between arcs. These processes are associated with the collision and subduction of hot and rheologically weak lithosphere of the arc. Subduction erosion of forearc slopes has been documented in the Japan Trench in relation to the subduction of graben features and seamounts. The most important inference drawn from the forearc evolution of the Japanese islands is that the majority of the continental crust in these island arcs was formed by the accretion of sediments and the intrusion of granites and that a part of this was eroded later and subducted. This process offers a global implication as to how continental crust has evolved throughout the Earth's history.