Balance of solid and fluid transfers near the updip limit of the seismogenic zone at the scale of all subduction zones in a revised kinematic framework

The nature and amount of sediments transferred from one plate to the other near the subduction interface partly determine the tectonic and seismogenic regime of a margin. Examination of over 500 multichannel seismic lines has enabled us to build a global database of subduction zone front characteristics at unprecedented spatial resolution. The total thickness of sediments in the trench below the deformation front, as well as that of the subduction channel at a distance from the trench, combined with other indices, such as the tectonic regime of the forearc or the migration of the volcanic front, are used to revisit the accretionary or erosional character of active margins.

The integration of our observations over the last million years has been achieved in parallel with a revision of the kinematics of subduction zones, taking into account deformation at the front of the thrust plate. Indeed, subduction zones are often the site of distributed or localized deformation up  to several hundred kilometers away from the plate boundary. Taking the "arc sliver zone » deformation into account yields a more accurate estimate of the effective long-term slip velocities (modulus, azimuth) on the subduction interface, which is fundamental to properly estimate material flow transiting towards the mantle.

Preliminary conclusions, based on ∼3/4 of sufficiently documented subduction zones, show a predominance of the erosive character of subduction over the last million years. The flux of solid sedimentary matter through the shallow part of the subduction channel is approximately 1.5 km³/yr, and that of pore fluids 0.4 km³/yr. Some subduction zones, such as the Aegean-Cyprean one, are characterized by exceptional solid flux in the channel, whereas the fluid flux is comparatively moderate. This is because channel sediments are compacted even before being subducted. Indeed, porosity has a major influence in estimating these fluxes, maximum porosity in the channel being reached when there is neither accretion nor tectonic erosion. Overall, fluid flux in the channel is greater under erosive margins, due both to the higher rate of subduction and often higher porosity. The data are displayed over 260 transects across subduction zones thanks to the Submap web-tool (www.submap.fr).