Publications

During subduction of an oceanic plate beneath a continent material may be exchanged between the downgoing plate and the overriding plate. The amount and nature of material potentially being transferred to the forearc mainly depends on the composition and fluid content of the sediment cover entering a convergent margin at the deep sea trench. A wealth of geophysical data acquired during the past few decades clearly images different styles of sediment accretion at convergent margins. Accretionary wedges comprising an onshore portion, e.g. the rear 200 km of the Makran accretionary prism or paleo-accreted material now found onshore (e.g. Hirono and Ogawa, 1998) demonstrate that sediment accretion contributes to continent growth. However, about half of the entire world’s margin length is non-accretive (von Huene and Scholl, 1991, Scholl and von Huene, 2001). At these margins, the forearc may lose considerable material through subduction erosion. During accretion, sediment porosity loss not only results from vertical compaction but additionally from lateral tectonically driven porosity loss. Fluids being released by this process or chemical reactions, e.g. the smectite-illite transition, may considerably contribute to overpressuring (Bekins et al., 1995, Saffer and Bekins, 1998) and also significantly affect the wedge’s thermal state (Kukowski and Pecher, 1999). Porosity distribution and released fluids also control the amount of solid and fluid fraction of material coming to the forearc - only the solid fraction of the incoming material may contribute to continent growth. The structure, lithology, and tectonic history of forearcs as identified from geophysical and geology field observations hint to parameters possibly controlling material transfer at convergent margins. Among them, sediment supply, width of the subduction channel, and interplate frictional properties, which also exhibit control on plate coupling and therefore the seismic potential of a forearc, are suggested to be of major importance. To quantitatively understand the complex and coupled processes underlying material and fluid flux as well as related deformation, the combined employment of numerical and analogue simulation is the first choice strategy. Mirroring this concept, this contribution evaluates parameters controlling material transfer at convergent margins and the influence of fluid release and transport on forearc mechanics by reviewing recent analogue and numerical simulation studies. Similarities and differences between erosive and accretive margins will be discussed by addressing the central Andean margin as a long-term tectonically erosive forearc and the Makran (Figure 1) margin, which exhibit the largest amount of sediment supply among the Earth’s margins, respectively.

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Kukowski, N. (2004): Material and Flux at Convergent Margins: What ends up in the Forearc?. GeoMod 2004 (Emmetten, Switzerland 2004).