NW-SE structural segmentation of the south-central Chilean offshore fore-arc (35S-40S)
Abstract
One of the targets of RV SONNE cruise 161, as part of the German-Chilean joint venture to study Subduction Processes Off Chile (SPOC), was the Central Chilean margin between Concepcion and Valdivia. Structural analysis of the slope and trench has been conducted from high resolution bathymetric data, aided by GIS and statistical procedures, as well as multichannel reflection seismic profiles. Geological features such as the subduction front, major thrust units in the accretionary prism, the westernmost seismic signature of the Paleozoic metamorphic rocks and the shelf edge were mapped. Structurally, the slope is dominated by NW-SE striking sinistral strike-slip faults and conjugate NE-SW and NNE-SSW oriented lineaments. Sinistral 120 o strike-slip faults are well known from on-shore Chile. The geometrical arrangement of these fault sets dissects the slope into rhomb shaped, tilted fault blocks. Simultaneous block rotation leads to development of graben and half-grabens. The lower slope is built up of a relatively small accretionary prism. Here NE-SW and NNE-SSW striking features correspond to the boundaries of major thrust units and anticlines. Lateral displacement of the thrust units along the NW trending strike slip lineaments ranges in general from about 10 km to 20 km south and from 2 km to 5 km north of 37 o30textquoteright S. Strike-slip faulting of even the youngest folds at the deformation front demonstrates recent mutual frontal accretion and strike-slip movement of the deforming backstop. The observed brittle deformation of the fore-arc fits well with structures encountered on-shore. The complex structural pattern can be explained by a model of margin-parallel shear, driven by oblique subduction.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....12950B