Kametoshi Kanmera, 1974. "Paleozoic and Mesozoic Geosynclinal Volcanism in the Japanese Islands and Associated Chert Sedimentation", Modern and Ancient Geosynclinal Sedimentation, R. H. Dott, Jr., Robert H. Shaver
Download citation file:
The main part of the Japanese Islands consists of the middle and late Paleozoic and the early Mesozoic eugeosynclinal sequences containing voluminous volcanic beds. The change through time and space of the nature of the volcanic rocks and the lithologic assemblages of the Paleozoic sequences suggest that they were formed in an ancient marginal or interarc basin and on the outer flank of a migrating ridge. The basin is presumed to have been initiated by a volcanotectonic rift zone that was associated with silicic tuffs and flows and coralline limestones during Middle Silurian to Middle Devonian time. This was followed by the crustal extension that resulted in the separation of the Kurosegawa-Abukuma-South Kitakami insular ridge from the Hida belt to form a marginal basin during Late Devonian to Middle Permian time. Thick eugeosynclinal deposits, including mafic volcancics and chert, accumulated concomitantly in the spreading basins.
In the early stage (Late Devonian to Early Carboniferous) of basin spreading, alkaline basalt was produced in association with a large amount of gabbroic rocks and serpentinite, which are assumed to be an oceanic basin crust created along the basin axes. In the later stage (Late Carboniferous to middle Permian) flow rocks and pyroclastics of mainly alkaline, partly tholeütic basalt dominated. They are conformably intercalated in clastic sediments, and they are arranged in an alternating en echelon pattern of a few to several linear volcanic zones. Two zones of ophiolitic assemblages, the Mikabu Green Rocks (Early Permian) and the Yakuno Basic Rocks (Middle Permian), are interpreted to have occurred as short-lived volcanic rises within the marginal basin.
The Triassic and Cretaceous mafic volcanic zones respectively were remarkably stepped southward along with the shifting of the main sedimentary basin to the outer side. This shifting was almost coeval with the orogenic events in the main sedimentary basin during the preceding Paleozoic ages.
The mafic volcanic rocks are commonly accompanied by bedded chert, and a rhythmic interlayering of tuff and chert is most characteristic. The cherts consist essentially of Radiolaria, some sponge spicules, their fragments, and a small amount of aphanitic material, probably volcanic clay. Their sedimentary features and intimate association with tuff suggest that chert beds accumulated rapidly because of an enormous supply of siliceous organisms. These organisms perished episodically in great masses when explosive submarine eruptions at depths not greater than 500 m resulted in heated water columns rising to the surface and spreading detrimentally among the plankton populations.