Rapid Subsidence and Tectonic Erosion of the Continental Margin off Northern Chile

The continental margin off Northern Chile was studied by bathymetric mapping (von Huene et al. 1999), multichannel seismic profiling, and sampling by piston corers and dredges to investigate the intense tectonic erosion of this convergent margin. Coccoliths and Sr-isotopes were used to define the stratigraphic age and depositional environment of sediments and related seismic sequences. The slope sediments consists of Pleistocene to middle Miocene siliceous hemipelagic silty clay, turbiditic sequences and rare shallow-water carbonates . The combination of stratigraphic data and sedimentological analyses reveal for two ridges on the upper slope (off Iquique and Antofagasta) a sequence of vertical movements around sea level comparable to the late Miocene to present movements of the Mejillones peninsula. A rapid subsidence of more than 1 mm per year affects the middle to outer slope. The landward dipping of small piggy-back basins indicates listric faulting probably related to large-scale slumping along shallow faults affecting the upper section of sediment. The main component of the rapid subsidence is thought to be caused by tectonic erosion above the descending oceanic crust causing the ablation of the overriding continental plate.