On the Northwest Pacific Tectonic Zone-Supplements to

As already interpreted by the writer in “The Korea-Japanese Tectonic Zone” 1976, the Northwest Pacific Tectonic Zone can be geologically comparable with that having the frontal orogenic belt represented by the Alps-Himalayan Mounts. It covers an extensive area in the eastern part of Eurasiatic continent, the western limit being demarcated by the Baikal Rift System, extending northeasterly about 2, 000 km in Siberia, and is constructed of the structural zones mentioned below, which are combined intimately with each other by mutual relationship in genesis.<BR>1 : Zone of continental massives characterized in structure by tension faults of the limited directions, NE-SW, NW-SE, E-W, etc. together with grabens and tilted blocks, accompanied by tension faults (Fig. 1).<BR>2 : Frontal orogenic belt represented by a series of insular arcs mostly with convex side towards the Pacific Ocean, and characterized with compound zonal structure shown by beds of various ages, complicatedly folded and disjuncted by shear faults (Fig. 2 and 3).<BR>3 : Marginal seas with troughs probably of a rift and structural basin origin, on the inner side of insular arcs.<BR>4 : Deep sea trenches developing along the outer side of insular arcs.<BR>Each of the insular arcs together with the troughs and the deep sea trenches along the insular arcs constitutes structural sectors as shown in Fig. 6.<BR>The fundamental pattern of the above structures is insisted to have been developed step by step by the crustal movements of the Jurassic, the Late Cretaceous-Early Tertiary, the Mid-Tertiary and the Neogene-Pleistocene ages.<BR>On the origin of the insular arcs and marginal sea basins, various opinions and hypotheses, based upon geological or geophysical investigations, have been presented, although many problems unsolved have been remained because of insufficient data. So far as the Northwest Pacific Tectonic Zone is concerned, however, geological facts demonstrated by observations on the earth surface, imply that firstly the characteristic structures of the insular arcs, above mentioned, may be best explained by the concept of compressional forces repeatedly worked to have lifted into folds and thrusted up the insular arcs towards the Pacific Ocean and nextly that the insular arcs have been drifted oceanwards away from the continent. The movements would cause downwarping of the oceanic crust to form the deep sea trenches.<BR>Figs. 1-9, newly provided here may elucidate in a certain extent recent ideas of the writer on the global tectonics in the Tectonic Zone in question.