Extensional stresses in the Colombian Eastern Cordillera fold-and-thrust belt (northern Andes): insights from 2D finite element modeling

Deformation and stress characteristics in the upper crust of the fold-and-thrust belt in the Colombian Eastern Cordillera were investigated by numerical analysis. The structural trend of Colombian Eastern Cordillera has long been considered a possible example of a true contraction orogen. The issue of the convergent displacement along an elastic structural body, which controls present-day deformation in this Cordillera is examined here. Modeling results are presented in terms of three parameters: 1) distributions, orientations, and magnitudes of principal stresses; 2) maximum shear stress (tau(max)) contour; and 3) proximity to failure of elements within faults. Mohr-Coulomb failure criteria with bulk rock properties are applied to analyze the faults. The model shows extensional stresses in the crust at shallow crustal levels (from surface to about 6 km) despite overall contraction, and contraction at depth is confirmed. Measurement results indicate that, for homogeneous crustal thickening, extensional stresses are concentrated in the Servita half-gaben and Bucaramanga fault systems, where the vertical thrust faults and thickening processes are located. Our two-dimensional (2D) modeling results emphasize that extensional stresses are still active along the vertical to sub-vertical fault system in the fold-and-thrust belt of the Colombian Eastern Cordillera.