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Book Chapter

Implication of dark bands in Miocene–Pliocene accretionary prism, Boso Peninsula, central Japan

By
Yoko Michiguchi
Yoko Michiguchi
Doctoral Program in Earth Evolution Sciences, University of Tsukuba, Tsukuba 305-8572, Japan
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Yujiro Ogawa
Yujiro Ogawa
Doctoral Program in Earth Evolution Sciences, University of Tsukuba, Tsukuba 305-8572, Japan
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Published:
August 2011

Thin, planar, dark, lamination-like bands are found in host siltstones in the Miocene-Pliocene metamorphosed Miura-Boso accretionary prism, southern Boso Peninsula, Japan. We classified the bands into four types on the basis of distribution, crosscutting relations, and internal textures. Type 1-1 dark bands are developed parallel to the bedding plane and do not include crushed or deformed grains within the band. Type 1-2 bands are also developed parallel to the bedding plane, but grain alignment within the band cuts obliquely across that in the host rock. Type 2 bands include ductilely deformed grains similar to an S-C′ structure, whereas type 3 bands have cataclastic grains. All the dark bands except type 1-1 (being an open fracture with little displacement) are shear bands or slip planes formed from sedimentation to accretion, although the formation mechanisms between the four types are different. These deformation bands are affected by the state of consolidation and magnitude of stress during formation, reflecting the deformation processes. Type 1-1 bands show evidence of independent particulate flow from excess pore-fluid-pressure generation, which occurs just after sedimentation. Type 1-2 bands are flexural-slip faults formed during formation of folds; type 2 bands are sliding planes formed from submarine landslides, whereas type 3 bands are thrust faults formed during accretion.

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GSA Special Papers

Mélanges: Processes of Formation and Societal Significance

John Wakabayashi
John Wakabayashi
Department of Earth and Environmental Sciences, California State University, Fresno, Fresno, California, USA
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Yildirim Dilek
Yildirim Dilek
Department of Geology, Miami University, Oxford, Ohio, USA
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Geological Society of America
Volume
480
ISBN print:
9780813724805
Publication date:
August 01, 2011

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