Episodic accretion and metamorphism of Jurassic accretionary complex based on biostratigraphy and K-Ar geochronology in the western part of the Mino-Tanba Belt, Southwest Japan
Episodic accretion and metamorphism of Jurassic accretionary complex based on biostratigraphy and K-Ar geochronology in the western part of the Mino-Tanba Belt, Southwest Japan
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DOI：
10.1111/j.1440-1738.1996.tb00034.x
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发表时间：
1996-09
期刊：
影响因子：
1.5
通讯作者：
M. Takami;T. Itaya
中科院分区：
文献类型：
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作者：
M. Takami;T. Itaya
位于日本西南部米诺-潭坝带西部的低级变质侏罗纪增生杂岩是一种由泥质基质和其他块状硅质岩、绿岩、硅质泥岩、陆源砂岩和泥岩组成的混沌沉积杂岩。该杂岩被划分为三个不同的地质单元，即单元I、单元II和单元III，它们之间有构造边界(逆冲)，形成了桩-推覆结构。它们在岩性、化石时代、变质条件和K-Ar年龄等方面具有不同的特征。微化石研究表明，三个单元的吸积时间分别为早侏罗世早期(约195 Ma)、中侏罗世早期(约175 Ma)和晚侏罗世(约147 Ma)。另一方面，从三个单元的泥质岩石中分离出的白色云母K-Ar年龄测定表明，随后与俯冲有关的变质作用发生在每个单元吸积后2300万年。这些结果有力地表明，日本西南部米诺-坦巴带西部的中生代期间发生了断续的增生和变质作用，时间间隔为2000~2800万年。
The low grade metamorphic Jurassic accretionary complex in the western part of the Mino-Tanba Belt, Southwest Japan, is a chaotic sedimentary complex which consists of argillaceous matrices with allochthonous blocks of chert, greenstone, siliceous mudstone, terrigenous sandstone and mudstone. The complex is divided into three distinct geologic units, Units I, II and III, with a tectonic boundary (thrust) between them, forming a pile-nappe structure. They have different features for lithologies, fossil age, metamorphic condition and K-Ar age. Microfossil researches revealed that their timings of accretion were in the early Early Jurassic (ca 195 Ma) for Unit III, in the early Middle Jurassic (ca 175 Ma) for Unit II and in the latest Late Jurassic (ca 147 Ma) for Unit I. On the other hand, K-Ar age determinations of white mica separated from pelitic rocks of the three units clarified that the subsequent subduction-related metamorphism was 23 million years after the accretion of each unit. These results strongly suggest that the accretionary and metamorphic process had taken place episodically with an interval of 20 to 28 million years during Mesozoic time in the western part of the Mino-Tanba Belt, Southwest Japan.