Style of fluid flow and deformation in and around an ancient out-of-sequence thrust: An example from the Nobeoka Tectonic Line in the Shimanto accretionary complex, Southwest Japan |
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| Authors: | Hideki Mukoyoshi Tetsuro Hirono Hidetoshi Hara Kotaro Sekine Noriyoshi Tsuchiya Arito Sakaguchi and Wonn Soh |
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| Institution: | Marine Works Japan, Yokohama 236-0042, Kanagawa (email: ),;Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka 560-0043,;Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, 305-8567,;Institute of Fluid Science, Tohoku University, Sendai 980-8577,;Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579,;Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokohama 236-0001, and;Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku 783-8502, Japan |
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| Abstract: | To understand the characteristics of deformation of an out-of-sequence thrust (OST) and the style of fluid flow along it, we investigated the Nobeoka Tectonic Line, which has been interpreted as a deep OST (7–9 km), in the Shimanto accretionary complex, Southwest Japan. The shear zone in the footwall differs significantly in the along-strike direction not only in thickness, which varied from 100 to 300 m, but also in lithology and mineral vein development. These variations might reflect primarily differences in lithology; that is, the sandstone-dominant shear zone with a large amount of mineral veins precipitated in microcracks is relatively thick, whereas the shale-dominant shear zone with a small amount of veins and with textures indicating highly pressurized pore fluid, is thinner. By comparison with characteristics of a shallow OST (3–5 km), we conclude that the shallow OST has experienced repeated brittle failure with rapid slip and focused fluid flow whereas the deep OST has experienced both brittle and ductile deformation, followed by fluid flow of various styles, depending on the lithology. |
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| Keywords: | cathodoluminescence fluid flow illite crystallinity Nobeoka Tectonic Line out-of-sequence thrust Shimanto accretionary complex |
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