Late Palaeozoic to early Mesozoic geodynamic evolution of the Circum-Pacific orogenic belt in South Korea and Southwest Japan

Abstract

A review of the overall features of the late Palaeozoic-early Mesozoic orogen of Southwest Japan and its Korean hinterland allows a new geodynamic model for the building of the east Asian margin to be proposed. During middle Carboniferous to early Permian times, an oceanic basin formed in a passive margin environment at a moderate spreading rate as the Honshu continental block drifted away from the Sino-Korean continent. During that period, paralic platform conditions and extensional synsedimentary tectonics prevailed in Korea. In middle Permian times, the closure of the oceanic area was responsible for Yakuno ophiolite obduction and high pressure metamorphism while highly subsiding coal basins developed in the emerged Korean hinterland. Thereafter, in late Permian times, when the Honshu block collided with the Asian margin (Akiyoshi orogeny), locally derived terrestrial clastic sedimentation in Korea has succeeded coal measure deposition with local unconformity. In early Triassic times, the collision was completed and regional uplift of the thickened crust resulted in the deposition of thick distal siliciclastic rocks in rapidly subsiding hinterland troughs (Korea) and flyschoid deposition in the Tamba foreland basin (outer zone of Southwest Japan). Middle to late Triassic medium- to low-pressure metamorphism, large-scale transcurrent tectonics and associated calc-alkaline synkinematic plutonism in the Hida and Ogcheon belts represent a post-collisional feature of the Akiyoshi orogenic event. Post-tectonic intrusives and terrestrial deposits post-date intracratonic tectonics at ca. 200 Ma. Thus, the Akiyoshi orogeny of Southwest Japan is a result of continental drift and ensuing collisional rewelding of a fragment of Sino-Korea: the Honshu microcontinent.