Deformation of accretionary wedges in response to seamount subduction: Insights from sandbox experiments

Sandbox experiments, using a two-dimensional and a three-dimensional approa ch, are used to study the deformation of margins in response to seamount su bduction. Successive mechanisms of deformation are activated during the sub duction of conical seamounts. First, reactivation of the frontal thrusts an d compaction of the accretionary wedge is observed. Then, back thrusting an d, conjugate strike-slip faulting develops above the leading slope of the s ubducted seamount. The basal decollement is deflected upward in the wake of the subducting high, and a large shadow zone develops behind the seamount trailing slope. Consequently, frontal accretion is inhibited and part of th e frontal margin is dragged into the subduction zone. When the main decolle ment returns to its basal level in the wake of the seamount, the margin rec ords a rapid subsidence and a new accretionary wedge develops, closing the margin reentrant. The sediments underthrusted in the wake of the seamount i nto the shadow zone, are underplated beneath the rear part of the accretion ary wedge. Substantial shortening and thickening of the deformable seaward termination of the upper plate basement, associated with basal erosion is o bserved. Seamount subduction induces significant material transfer within t he accretionary wedge, favors large tectonic erosion of the frontal margin and thickening of the rear part of the margin. The subduction and underplat ing of relatively undeformed, water-ladden sediments, associated with fluid expulsion along the fractures affecting the margin could modify the fluid pressure along the basal decollement. Consequently, significant variations of the effective basal friction and local mechanical coupling between the t wo plates could be expected around the subducting seamount.