A visage of early Paleozoic Japan: Geotectonic and paleobiogeographical significance of Greater South China

Abstract

The current state of knowledge on the early Paleozoic evolution of Japan is reviewed. Although early Paleozoic Japan marked the foundation of long-lasting subduction-related orogenic growth throughout the Phanerozoic, details of this have not been fully revealed. Nevertheless, U-Pb dating of zircons both in Paleozoic granitoids and sandstones is revealing several new aspects of early Paleozoic Japan. The timing of the major tectonic change, from a passive continental margin setting (Stage I) to an active one (Stage II), was constrained to the Cambrian by identifying the oldest arc granitoid, high-P/T blueschist, and terrigenous clastics of arc-related basins. Ages of recycled zircons in granitoids and sandstones provided critical information on the homeland of Japan, i.e. the continental margin along which proto-Japan began to grow. The early Paleozoic continental margin that hosted the development of an arc-trench system in proto-Japan had cratonic basement composed mostly of Proterozoic crust with a minor Archean component. The predominant occurrence of Neoproterozoic zircons in Paleozoic rocks, as xenocrysts in arc granitoids and also as detrital grains in terrigenous clastics, indicates that the relevant continental block was a part of South China, probably forming a northeastern segment of Greater South China (GSC) together with the Khanka/Jiamsi/Bureya mega-block in Far East Asia. GSC was probably twice as large as the present conterminous South China on mainland Asia. Paleozoic Japan formed a segment of a mature arc-trench system along the Pacific side of GSC, where the N–S-trending Pacific-rim orogenic belt (Nipponides) developed with an almost perpendicular relationship with the E–W-trending Central Asian orogenic belt. The faunal characteristics of the Permian marine fauna in Japan, both with the Tethyan and Boreal elements, can be better explained than before in good accordance with the relative position of GSC with respect to the North China block during the late Paleozoic.