Smectite swelling in the Miura–Boso accretionary prism: Possible cause for incipient décollement zone formation

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書誌事項

公開日
2010-10
資源種別
journal article
権利情報
  • https://www.elsevier.com/tdm/userlicense/1.0/
DOI
  • 10.1016/j.tecto.2010.08.008
公開者
Elsevier BV

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説明

Abstract An analysis of the mineralogy of the Miura–Boso accretionary prism, which consists of off-scraped upper Miocene strata exposed on the southern parts of the Miura and Boso peninsulas in Central Japan, revealed homogeneous mineral composition throughout all levels of silt layers hosting deformation structures associated with sediment accretion. XRD analyses showed that the sediment consists of randomly ordered mixed layer illite–smectite (I–S) with low illite content (> 40 wt.%), quartz (30 wt.%), illite (10–20 wt.%), plagioclase (10 wt.%), kaolinite (+ chlorite) (5 wt.%), and calcite (0–10 wt.%). The observed mineralogical assemblage indicates that location of the decollement formation was not constrained by mechanical heterogeneities associated with mineralogical variations, but was controlled by spatial variations in effective pressure. Within the over-consolidated sediment located above the incipient decollement zone, the occurrence of abundant smectite with a shape-preferred orientation gave rise to smectite swelling, producing pressures in the order of ~ 3.0 MPa. The combined effect of high swelling pressure and high pore pressure resulted in an overpressured zone at the base of the over-consolidated zone, facilitating the development of a decollement zone within the prism.

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