THE CENTRAL SUB-ANDEAN FORELAND BASIN: AN ANALYSIS OF THE FLEXURAL WAVE COUPLED TO BASIN SHORTENING

Foreland basins exhibit a diagnostic asymmetrical profile which mostly evolves as a response to the growth of tectonic load and its progressive propagation basinward. The leading result of the convergence rate and propagation of the deformation front is the migration of the flexural wave in space through time. One of these modern tectonic settings is the Central Sub-Andean of southern Bolivia, a thin-skinned deformation system pushed by the bounding Altiplano block.

Our analysis rely on the interpretation of key stratigraphic levels in order to define periods of migration of the subsiding depozones, aiming to model the flexural profile along a cross-section for these time steps: at 7.5 Ma; 5.5. Ma; 2.5 Ma; and present day. As a result, it was revealed that there is a progressive weakening of the elastic beam coeval to the migration of the tectonic load. This progressive weakening accounts for absorbing the increasing tectonic load created by major thrusting, which in turn triggers new frontal thrusts ahead ruled by the critical wedge state.

Supported by the flexural model of subsidence, we calibrated the interpreted subsurface geology by sequential forward modeling of shortening along the given cross-section. Prevailing structural style of deformation in the region guided the solution of hidden sub-thrust spaces, and the flexural profiles for major steps highlighted the importance of resulting basal detachment morphology on location of evolving new thrusts. Our shortening modeling potentially unravels mechanisms of foreland basin thrusting and folding as a dynamic response to the migration of the flexural wave.