Toward a dynamic concept of the subduction channel at erosive convergent margins with implications for interplate material transfer

Abstract

[1] Convergent plate boundaries accommodate intraplate displacement within a $100-1000 m thick shear zone. Marine geophysicists typically define this zone, the subduction channel (SC), as the sedimentary layer between the downgoing oceanic crust and the base of the upper plate. Geologists and modelers, instead, perceive the SC as a specific type of shear zone. The original theory of SCs was developed when the net accretion of marine sediments to the forearc was thought to typify a convergent margin. While erosive margins were briefly mentioned, their mechanics were not discussed in any detail. We now realize that subduction erosion is taking place at roughly half of the modern subduction margins. Here we review and revise the theory of erosive SCs (1) to unify this concept across disciplines, focusing on the meaning of the channel's boundaries; (2) to redefine the portions of the forearc included in the SC concept; and (3) to better idealize this dynamic system where material supply to the channel, fluid content, and the heterogeneity of deformation all influence the SC's upper and lower boundaries. Migration of the channel boundaries controls the downdip variation of tectonic mechanisms that shape the margin. Within the shallow, <15 km deep part of the SC, a gradual change of physical properties defines three zones; zone 1 of rapid fluid dewatering, zone 2 of overpressure, and zone 3 with metamorphic fluid release. A SC is a dynamic feature with along-strike and downdip variations caused by changes in channel material, in trapped fluid contents, and in interplate boundary geometry.

Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

“…thick shear zone (e.g., Vannucchi et al, 2012). This is an important question that needs to be resolved but is somewhat outside the scope of this review.…”

“…The dipping LVZ observed in nearly all subduction zones worldwide is undoubtedly associated with material being entrained into the subduction zone (Bostock, 2013;Vannucchi et al, 2012). The exact nature of this material is debated, however, and has been interpreted either as some portion of the downgoing oceanic crust containing meta-basaltic rocks, subducted sediments, upthrusting serpentinite from the mantle wedge, or a tectonic "melange" composed of some or all of these elements and forming a…”

Late Oligocene–early Miocene olistostromes (sedimentary mélanges) as tectono-stratigraphic constraints to the geodynamic evolution of the exhumed Ligurian accretionary complex (Northern Apennines, NW Italy)

“…Observations on modern accretionary complexes in convergent plate boundaries show that the outer wedge is highly sensitive to changes of the dynamic equilibrium (e.g., Davis et al 1983;Platt, 1986;Del Castello et al 2004von Huene et al 2004;Sage et al 2006;Vannucchi et al 2012). In this framework, mass-transport processes are leading agents in maintaining the dynamic equilibrium by reshaping the accretionary wedge topography and producing high concentration of small-to medium-scale submarine landslide accumulations (McAdoo et al 2004;Mosher et al 2008;Camerlenghi et al 2009;Moore et al 2009;Harders et al 2011;Strasser et al 2011) and megaslides (Moore et al 1976;Golfinger et al 2000;Cochonat et al 2002;von Huene et al 2004;Hühnerbach et al 2005;von Huene, 2008;Yamada et al 2010).…”

IODP Expedition 334: An Investigation of the Sedimentary Record, Fluid Flow and State of Stress on Top of the Seismogenic Zone of an Erosive Subduction Margin

“…Thus, to assess the thickness of the subduction channel (Vannucchi et al, 2012b, and references therein) the mass removed from the upper plate has to be estimated, which can be achieved based on subsidence profiles determined from the cored slope sediments.…”