Chapter 2 - Control of subduction erosion and sediment accretion processes on the trench curvature of the central Chilean margin

Abstract

The Juan Fernández Ridge (JFR) is a hotspot track that is currently subducting off central Chile (32°–33°S). In this region, a fundamental change in trench curvature (in plan view) and sedimentation occurs near the collision zone between the JFR and the Chile Trench. Subduction erosion and sediment accretion have been active north and south of this collision zone. Here, I show a compilation of wide-angle seismic profiles in the area surrounding the collision zone in order to compare the seismic structure of the contact between the accretionary prism and continental basement. The seismic results north of the collision zone show that the toe of continental basement is ~5–10km landward of the trench, whereas the contact between the accretionary prism and continental basement south of the collision zone is situated 50–60km landward of the deformation front. The plan-view curvature of the continental basement toe is constrained by seismic results to have a value of ~0.793×10−3km−1. This value, which accounts for only ~30% of the overall trench curvature, is related to the mechanical behavior of continental basement and is predominantly controlled by regional-scale processes such as deep subduction of the JFR and slab rollback. The remaining trench curvature can be explained by subduction erosion and sediment accretion.