琉球島弧系の地球物理学的研究
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概要
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Seismic profiler records and proton-magnetometer data obtained in the East China Sea and the Ryukyu Island Arc are analysed. On the contiental shelf of the East China Sea, an acoustic basement is detected under sedimentary layer of 0.5-1 km thickness. According to sonobuoy refraction studies in eastern half part of the shelf (LEYDEN et al., 1973), the basement is thought to be a reflector in Pliocene sedimentary layer. In the deep plain of the Ryukyu Trough, two or three sedimentary layers are detected and the uppermost opaque layer of them is assumed to be turbidite. From the point of the continuity of sedimentary layers on the west slope of the trough, it is presumed that the trough was formed probably, in Pliocene or later as a result of crustal movement. In an eastern half part of the trough, many small seamounts of volcanic origin are observed. Near axis of the Ryukyu Arc and on the island slope, geomagnetic anomaly is very small. M_1-M_1 line in Fig. 1 shows a boundary line between calm area and moderately disturbed one, geomagnetically. As shown is Fig. 5,double amplitude of magnetic anomaly profiles in the eastern half part of the continental shelf is not much different from ones of the Japan or Philippine basin. And, as determined by seismic studies, depth of crystalline basement under the sea level in the eastern half part of the East China Sea is also not much different from ones in the Japan or Philippine Basin, From the above facts, the weiters wish to presume that an old hidden marginal trough belonging to the Ryukyu Arc may exist west off the present trough.
- 国立科学博物館の論文
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