The Triassic Akiyoshi Orogeny
published: Jan 1, 1955
The tectonic development of Europe was schematized by Professor STILLE (1924) in an excellent manner into the Eo-Palaeozoic Caledonian, Neo-Palaeozoic Variscan and Mesozoic and later Alpine cycles of orogeny, each of which being classified into a series of phases. The Bretonian, Sudetic and Asturian in the Carboniferous period are the three conspicuous phases and the Variscan cycle was declined already in the Permian (STILLE, 1951). Compared with the Palaeozoic era, Europe was stable in the Mesozoic, especially in the Triassic period when no phase of crustal deformation was witnessed by him except for the old Cimmerian near the end of the period. Therefore the Middle Triassic Akiyoshi orogeny of the Orient may be of special interest for occidental geologists. With this point in mind this subject is choosed for my article which is to be dedicated to Prof. HANS STILLE on the occasion of the celebration of his 80th birthday. The Akiyoshi Orogenic Cycle and Orogenic Sedimentation in Japan In Eastern Asia there was the Middle Palaeozoic disturbance, but neither intense nor extensive. The Palaeozoic era was relatively tranquil on the whole and several phases of movements named on the continent were mostly epirogenic rather than orogenic in nature. In the Mesozoic on the contrary vigorous crustal movements were repeated there. Japan is not an exception where Carboniferous and older discordances are all local or insignificant and no typical orogenic sediment is found below the Permian (MINATO, 1950). Commencing with the Chichibu geosyncline, the history of her mountain-building can be classified into the Permo-Triassic Akiyoshi cycle, Jurasso-Cretaceous Sakawa cycle and later Oyashima disturbances where the first cycle attained its zenith in the Middle Triassic period (KOBAYASHI, 1941).