Impact of sedimentation on evolution of accretionary wedges: Insights from high-resolution thermomechanical modeling

Abstract

Syntectonic sedimentation history is a potential cause of differentiated accretionary wedge structures along the subduction margin. Recent efforts to model the role of sedimentation on wedge evolution have highlighted the importance of spatiotemporal history of sedimentation on the evolution of the wedge. Moreover, reconstruction of deformation history of the accretionary wedges using reflection seismic and borehole data has further substantiated the impact of sedimentation on wedge evolution. We conduct several numerical experiments using a high‐resolution dynamic 2‐D thermomechanical plate subduction model to systematically investigate and quantify different effects of sedimentation on accretionary wedge evolution. Models with sedimentation suggest migration of deformation to parts of the wedge lying outside the sedimentation zone leading to emergence/reactivation of out‐of‐sequence thrusts (OOSTs). Frequency and length of new thrust sheets are correlated with sedimentation in the trench. Models undergo a transition period of ~1.5 Myr following the onset of sedimentation, after which they continue to grow under a new steady state. Stabilization of the wedge and increased load on the oceanic plate due to sedimentation create conditions in which smaller wedge‐top basins combine to form a large and flat forearc basin. Last but not the least, emergence of OOST in models of accretionary wedges undergoing sedimentation provides important insights in to evolution of potentially tsunamigenic OOSTs like the Megasplay Fault seaward of the Kumano forearc basin.

Rapid sedimentation and overpressure in shallow sediments of the Bering Trough, offshore southern Alaska

“…Pervasive overpressure in the shallow portion of the accretionary wedge therefore will tend to focus seismicity elsewhere, away from rapidly accumulating sediment. This process appears consistent with increased deposition offshore leading to a more widely spaced thrust system as shown for instance in models by Fillon et al [] and Mannu et al [].…”

Stratigraphic signatures of forearc basin formation mechanisms

“…The model setup represents a dynamic 2‐D, high‐resolution, thermomechanical, plate subduction model, previously documented in Mannu et al . []. The thermomechanical model is coupled to an adaptive irregular surface grid to model the free surface.…”

“…Unlike Mannu et al . [], we implement ponding sedimentation in a cascading fashion down consecutive depocenters and it is limited by a sediment flux. The specifications for a sediment flux includes a prescribed sediment budget ( ), a starting point, and direction ( ; for hinterland‐to‐trench, termed “hinterland sedimentation,” or conversely trench‐to‐hinterland, termed “trench sedimentation”).…”

“…In addition to these dominant sedimentation mechanisms, we superimpose a linear diffusion ( ) to simulate the effect of small‐scale sediment remobilization processes driven by gravity and bottom currents (as bed load) across areas with varying slope inclination to get a more realistic topography. We employ a mass conserving critical slope cutoff condition to avoid oversteepening of the deforming surface grid [ Mannu et al ., ]. It lowers the surface from the threshold angle of to at a given surface node pair.…”

“…The initial model is very similar to the previous study by Mannu et al . [] with a computational domain of 3500 km × 200 km discretized onto 1284 × 351 nodes. A 10 km thin layer of “sticky air” [ Crameri et al ., ] overlies the upper rock surface and corresponds to air (white in Figure ) or water (light blue in Figure ) in the model.…”