Total volume and latitudinal variations of the sedimentary trench-fill off Central and Southern Chile: A record of short and long-term geologic processes

The amount and composition of trench sediment that is underthrust in a subduction zone impacts on the physical state of the shallow megathrust. Knowledge about the sedimentary and tectonic state and the geologic history of a trench system is therefore an important step towards understanding the structural and seismotectonic evolution of a convergent margin. The Chilean Trench south of 32°S is a sediment-filled basin that stretches in N-S direction. Variations in trench-fill are directly linked to and controlled by a number of sedimentary-tectonic processes and their interplay over space and time. In this work we unravel the individual processes for a ~1500 km long segment of the Chilean trench (32°S-46°S) and investigate their temporal and spatial significance. We use swath bathymetric and reflection seismic data to produce grids of the seafloor and the surface of the subducting oceanic plate buried beneath the trench sediments. The volume of the sedimentary trench-fill and its along-strike variations are derived from the difference between the two grids. Our results indicate that the volumetric sediment distribution can be best explained by high sediment input in the south and active northward sediment transport along the trench during glacial periods. However, during interglacial periods, small-scale factors that locally modify the sediment input seem to dominate. For the future along-strike variations in sediment volume will be compared with variations in structure and seismic behavior of the margin.