超大陸と日本列島の起源

Abstract

The history of supercontinents is briefly reviewed in relation to the origin of the Japanese Islands. The Japanese Islands formed part of the S. China Block, which was a part of supercontinent Rodinia at 1.0 Ga. Rodinia was rifted at 600 Ma, separating S. China Block, N. America, Australia and other continents, to generate the Proto-Pacific Ocean in between. On the other hand, the Hida and Oki islands belong to the N. China Block, which has much longer history than the S. China Block, extending back to 1.9-2.0 Ga with minor older rocks dating back to 3.8 Ga. The 1.8-2.0 Ga high-grade gneiss in the Hida and Oki belts may be part of the 1.8-1.9 Ga Nuna/Columbia supercontinent within which N. China-Japan occurred at the NE corner, as judged from key parallel belts of 1.8-1.9 Ga in N. China. The position of Japan at 1.0 Ga within Rodinia was at the center together with S. China and western margin of N. China. The oldest fossiliferous rocks in Japan may extend back to the Early Cambrian to Ediacaran formed during the rifting of Rodinia directly after Neoproterozoic snowball Earth. Initiation of subduction began ca. 520 Ma, and evolved through five Pacific-type orogenies along the southern margin of S. China. On the other hand, the Hida and Oki belts suffered the Triassic collision orogeny at 230-240 Ma, involving platform sediments up to the Carboniferous age. The final tectonic emplacement above the Jurassic accretionary complex may be related to the extensional event during the opening of the Japan Sea in the Miocene.