Andean foreland evolution and flexure in NW Argentina: Chaco–Paraná Basin

Abstract

The Chaco–Paraná Basin was initiated during the late Oligocene as a result of shortening in response to Nazca–South America plate convergence, which produced a fold and thrust belt in the backarc region of the Central Andes. Foreland basins are the result of the flexural isostatic response of an elastic plate to orogenic and/or thrust sheet loading. We carried out flexural modeling along a W–E profile (22.5°S) to determine flexural, crustal, and Chaco–Paraná foreland basin development using available information on ages, elastic and sedimentary thicknesses, topographic and structural histories. We also developed a 3D flexural model, considering present day topography and elastic thickness values, in order to assess the possible existence of major differences with 2D models. It is possible to reproduce present day elevation, gravity anomaly, Moho depth, elastic thicknesses, foreland sedimentary thicknesses and the basin geometry. The 2D modeling also permits to reproduce foreland sedimentary thicknesses documented at 10Ma and 12Ma. The new results indicate that any decrease of the elastic thickness beneath the Eastern Puna–Eastern Cordillera would have occurred during the 14–12/10Ma interval, suggesting a major change in the thermal state of the lithosphere during such time span. Coincidently, other authors determined the occurrence of a rapid elevation increase of the Southern Altiplano/Eastern Cordillera at 13–9Ma, possibly related to piecemeal removal of lower lithosphere. In spite of the numerous limitations and simplifications mentioned above, our flexural model has shown to be a useful tool for the better understanding of the relationships between the development of the Chaco–Paraná foreland basin and the spatiotemporal evolution of the Andean orogen.