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1 引 言 正如Ichikawa(1990)所归纳的,日本前白垩纪地体包括具有不同增生时代的两类增生复合体。一类是以秋吉地体为代表的二叠纪复合体,其增生时代为中二叠世晚期至晚二叠世早期,另一类增生复合体的增生发生在侏罗纪至早白垩世,它包括美浓地体及其相当体,北秩父地体,南秩父地体和北北上地体。 这些前白垩纪增生复合体通常以存在具各种岩石和年代的大洋岩石为特征。在这些大洋岩石中最特殊的是常被玄武岩下伏的巨大体积的晚古生代浅海相碳酸盐岩。它们通常与同时代的深海粉砂岩及相伴它的玄武岩共同出露。密切岩性关系的浅海相碳酸盐岩、深海相粉砂岩和玄武岩构成了二叠纪和侏罗纪地体内的大洋岩石组合。碳酸盐岩和粉砂岩分别被复原为玄武岩海山上的浅海岩帽和玄武岩海山周边的深水盖层。 晚古生代大洋岩石在前白垩纪地体内与陆源岩石表现为复杂相混。大洋岩石常表现为复盖在较年轻的主要为泥岩的陆源岩石上的巨大构造片。很多小型孤立大洋岩石体常混乱地夹入在泥岩内。由于又强调把年轻时代的相连陆源岩石作为外来方式出现的,故广泛采纳晚古生代大洋岩石是由古海山和相关沉积岩的残余组成的,它们是被碰撞到活动大陆边缘并与海沟充填物一起并入增生往的。 这些古地理和构造解释引起了一些新问题,即?
1 Introduction As Ichikawa (1990) concludes, the pre-Cretaceous terranes of Japan include two types of proliferative complexes with different proliferative age. One is the Permian complex represented by the Akiyoshi terrane. The accretion period is from the late Middle Permian to the early Late Permian, and the proliferation of the other accretionary complex occurs from Jurassic to Early Cretaceous. It includes the Mino and its equivalent, the North Chichibu, the Nanchuan and Northeastern Upper Triassic. These pre-Cretaceous accretionary complexes are often characterized by the presence of oceanic rocks with various rocks and ages. Of the most particular of these oceanic rocks are the massive Paleozoic marine facies carbonates that are often subducted by basalts. They are commonly associated with contemporaneous deep-sea siltstone and accompanying basalts. The close-tight lithology of shallow marine carbonates, deep marine siltstones and basalts make up the oceanic rock assemblages in the Permian and Jurassic terranes. Carbonates and siltstones were recovered as shallow-water rock caps on basalt seamounts and deep-water caprocks around basalt seamounts. Late Paleozoic oceanic rocks mixed with terrigenous rocks in the Precambrian terrane. Oceanic rocks are often characterized by huge tectonic plates overlain on the younger, mainly mudstone-derived terrigenous rocks. Many small isolated oceanic rocks are often trapped in muddy rocks. As a result of the emphasis on extraneous terrestrial rocks associated with young terrains, the late Paleozoic oceanic rocks were extensively composed of remnants of the ancient seamounts and associated sedimentary rocks that collided with active continental margins and with trenches Into the proliferation of the past. These paleogeographic and tectonic interpretations have caused some new questions, namely?