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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
Author(s) -
Takami Michio,
Itaya Tetsumaru
Publication year - 1996
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/j.1440-1738.1996.tb00034.x
Subject(s) - geochronology , geology , metamorphism , biostratigraphy , paleontology , accretion (finance) , geochemistry , physics , astrophysics
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.