Underplating of mélange evidenced by the depositional ages: U–Pb dating of zircons from the Shimanto accretionary complex, southwest Japan |
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| Authors: | Tadahiro Shibata Yuji Orihashi Gaku Kimura and Yoshitaka Hashimoto |
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| Institution: | Department of Applied Science, Kochi University, Kochi 780-8582, Japan (email: ),;Earthquake Research Institute, the University of Tokyo, Hongo, Tokyo 113-0032, Japan,;Department of Earth and Planetary Science, the University of Tokyo, Hongo, Tokyo 113-0033 Japan (email: ), Institute for Frontier Science,;Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan, and;Department of Natural Environmental Science, Kochi University, Kochi 780-8582, Japan |
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| Abstract: | Abstract Growth of an accretionary prism is effected by frontal accretion and deep subsurface underplating at the base of the prism. A systematic oceanward and structurally downward younging of underplated sequences is expected as the prism thickens and grows. To test this hypothesis and explore the processes of underplating, the U–Pb ages of zircon grains contained in underplated mélange sequences or packages of the Late Cretaceous and early Paleogene accretionary complex of the Shimanto Belt, southwest Japan, were determined using LA–ICP–MS laser technology. The results document systematic but intermittent younging ages within a single underplated mélange package. This finding suggests that underplating took place episodically during a period of several million years and that between episodes of underplating, a large amount of sediment was subducted to depths much greater than where underplating was occurring. |
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| Keywords: | accretion LA–ICP–MS mélange Shimanto Belt subduction |
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