A deep section of accretionary complex: Susunai Complex in Sakhalin Island, Northwest Pacific Margin |
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| Authors: | Gaku Kimura Masayuki Sakakibara Hisashi Ofuka Hideo Ishizuka Sumio Miyashita Makoto Okamura Olex A Melinikov Vilera Lushchenko |
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| Institution: | Department of Earth Sciences, Faculty of Education, Kagawa University, Takamatsu, 760 Japan;Department of Earth Sciences, Faculty of Sciences, Ehime University, Matsuyama, 790 Japan;Department of Geology, Faculty of Sciences, Kochi University, Asakura, Kochi, 780 Japan;Department of Geology and Mineralogy, Faculty of Sciences, Niigata University, Igarashi, Niigata, 950-21 Japan;Institute of Marine Geology and Geophysics, Sakhalin, Academy of Science, Russia |
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| Abstract: | Abstract A deep section of accretionary complex, the metamorphosed Susunai Complex, is observed on Sakhalin Is., Russia. High pressure part of pumpellyite-actinolite facies metavolcanics, metacherts and metapelites are well exposed and constitute a tectonic pile preserving primary structures related to underplating of the oceanic crust. Three stages of deformation, D1 through D3, suggest successive deformation during subduction, underplating and exhumation of the complex. Oceanic material in the complex is more abundant than other well documented ancient accretionary complexes (e.g. the Shimanto Belt in southwest Japan and the Ghost Rocks Formation in Alaska), which were shallowly underplated. At Susunai, deep down-stepping of a décollément has scraped off the upper part of the oceanic crust, primarily the pillowed basalt horizon. This down-stepping results from crustal weakening as overpressured water is released from the fractured oceanic crust during metamorphism. |
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| Keywords: | accretionary complex blueschist Sakhalin Susunai underplating |
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