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Exchangeable cation composition of the smectite‐rich plate boundary fault at the Japan Trench

Abstract : To better understand physicochemical processes in smectite-rich fault zones, we examinedexchangeable cation composition of samples from the slip zone of the 2011 Tohoku-oki earthquake(Mw9.0) recovered by the Integrated Ocean Drilling Program Expedition 343. Our chemical analyses revealedthat the exchangeable Ca2+and Mg2+are enriched in the slip zone, while Na+is depleted. K+shows acomplicated depth profile probably due to Kfixation. Based onfluid chemistry data, we estimated apparentselectivity coefficients of exchange reactions in the ternary Ca2+-Mg2+-Na+system. The results suggest thatthe Na+to Mg2+exchange reaction on smectite might have progressed in the slip zone. One explanationfor this feature is local progress of the reaction triggered by coseismic thermogenesis during the earthquake.Considering that the frictional property of smectite gouge is dependent on the exchangeable cationcomposition, chemical processes as observed in this study are intimately linked to physical aspect ofsmectite-bearing faults
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Jun Kameda, Chisaki Inaoi, Marianne Conin. Exchangeable cation composition of the smectite‐rich plate boundary fault at the Japan Trench. Geophysical Research Letters, American Geophysical Union, 2016, 43 (7), pp.3112-3119. ⟨10.1002/2016GL068283⟩. ⟨hal-02982553⟩



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