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在日本列岛岸外弧前区下面,从大洋板块直到加积棱柱体底部的声波基底表面上,可探测到一个明显的底部声波反射面。新近的研究表明,这一反射面不可能是俯冲大洋板块的上部界面,而只能是大洋玄式岩基底(或燧石层)的上部层位。和达—贝尼奥夫带的构造活动似乎是切割大洋基底与上覆沉积物边界的一种逆断运动,这些逆断层切断了底部反射面,並延伸进入了加积棱柱体之内。在大陆架与大陆坡之下中等及较浅深度上发生的大地震,是这些逆断运动的直接显示。在以往的地质年代中也发生过逆断活动。酸性和碱性岩浆(可能产生于中等深度的地震带)沿逆断层或伴生的正断层而上升。西南日本弧前区15—16百万年前,东北日本从22百万年前发生过侵入活动。接着,盆地在侵入体的向陆侧沉降。在一些情况下,弧前火成岩中还含有陆壳或洋壳的捕虏岩。这种弧前火成岩(包括捕虏岩在内),在日本列岛的二叠纪和三叠纪构造带中可以找到很好的例子。本文所举模式是日本列岛弧前区特有的模式。我们认为,在其它的弧前区,不同的构造参数(如会聚速率和沉积物供给)会引起不同的构造作用。
Below the offshore foreland area of the Japanese Islands, a pronounced bottom acoustic wave reflection surface can be detected from the oceanic plate up to the surface of the sound wave substrate at the base of the stacking prism. Recent studies have shown that this reflection plane can not be the upper interface of the subducting oceanic plate but only the upper horizon of the oceanic basaltic rock basement (or flintstone). The tectonic activity of the Heida-Benioff belt appears to be a reversing motion that cuts the boundary between the oceanic basement and the overlying sediments, which cut off the bottom reflector and extend into the accretion prism. The large earthquakes that occur at moderate and shallow depths below the continental shelf and the continental slope are the direct indications of these thrust movements. In the past geological age has also occurred in the anti-cut activities. Acidic and alkaline magmas (possibly resulting from medium-depth seismic zones) rise along thrust faults or associated normal faults. Southwest Japan Arc Prehistoric District 15-16 million years ago, northeast Japan from 22 million years ago had invaded. The basin then settled on the inland side of the invader. In some cases, pre-argillaceous igneous rocks also contain continental or oceanic crust. This pre-argillic igneous rock (including the pluton) can be found in the Permian and Triassic tectonics in the Japanese archipelago. The model presented in this paper is a unique model of the Pre-Arc in the Japanese Archipelago. We believe that different tectonic parameters (such as convergence rate and sediment supply) cause different tectonic settings in other pre-arc regions.