Abstract

Seismic investigations and scientific ocean drilling projects have documented a remarkable degree of geologic heterogeneity in marine forearc basins in convergent margins worldwide. The mechanisms for offshore basin formation and evolution are, however, often not completely understood, especially for erosive margins. This study integrates high-resolution bathymetry, seismic reflection lines, and refraction-based P-wave velocities to better understand the shallow structure of the northern Chilean erosive convergent margin between 19° and 21°S. The data resolve a regionally developed forearc basin, which contains the previously recognized upper slope-shelf Iquique Basin, and which reaches a maximum depth along the middle slope, containing up to 2 km of accumulated sediments. The basin geometry appears to be tectonically controlled by major north-south oriented crustal faults, which (to first order) govern the morphology and shallow structure of the marine forearc. We propose subsidence due to enhanced subduction erosion by high relief/seamount subduction as a mechanism for basin formation. Spatial correlation between the forearc basin and the highest slip area for the Iquique earthquake highlight the relevance of future studies to understand the relationship between the shallow structure of the marine forearc and the processes occurring on the subduction interface.