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本文根据反射地震、折射地震、磁力等资料,结合周边地质,探讨冲绳海槽南段基底组成。在海槽周边的东海陆架盆地、台湾褶皱带和琉球岛弧褶皱带,均出露不同程度变质的晚古生代、中生代和早第三纪地层。多道反射地震表明,海槽南段沉积盖层由上第三系和第四系组成,声学基底由下第三系及更老地层构成。邻近海槽的折射地震揭示,除第四系-中新统速度层之外,还存在纵波速度分别为4.7～5.3km/s和6.3km/s的下第三系和中生界速度层。磁异常分析和正反演拟合计算结果表明,海槽磁性基底主要由变质岩系构成,次为燕山期中酸性岩浆岩和喜山期中基性岩浆岩,磁性基底大部分相当声学基底。综合分析表明,海槽南段基底主要由不同程度变质的下第三系、中生界和上古生界构成;在海槽某些构造部位,已有喜山期基性岩浆岩形成。
In this paper, the basement composition of the southern part of the Okinawa Trough is discussed based on the data of reflected seismic, refraction seismic and magnetic force combined with the surrounding geology. In the East China Sea Shelf Basin, Taiwan Fold Belt and Ryukyu Island Fold Belt around the trough, both Late Paleozoic, Mesozoic and Early Tertiary strata of varying degrees were exposed. Multi-trace seismic reflection shows that the sedimentary cover of the southern section of the trough is composed of the Upper Tertiary and Quaternary facies, and the acoustic basement consists of the Lower Tertiary and older formations. The refraction earthquake near the trough reveals that besides the Quaternary-Miocene velocity layer, there are lower Tertiary and Mesozoic velocity layers with P-wave velocity of 4.7-5.3 km / s and 6.3 km / s, respectively. The results of magnetic anomaly analysis and forward-inversion fitting calculation show that the magnetic base of the trough is mainly composed of metamorphic rocks, followed by Yanshanian medium-acidic magmatic rocks and Xishishan-derived basic magmatic rocks, and most of the magnetic basalts are quite acoustic substrates. The comprehensive analysis shows that the basement of the southern part of the trough is mainly composed of the Lower Tertiary, Mesozoic and Upper Paleozoic metamorphic in varying degrees. In some structural parts of the trough, the Himalayan basic magmatic rocks have been formed.