Segmentation and growth of foothill thrust-belts adjacent to inverted grabens: the case of the Colombian Llanos foothills

Abstract

Abstract The geometry, kinematics and evolution of thick- and thin-skinned fold and thrust-belts have been characterized for many tectonic provinces. However, the impact of prior extension in the structural evolution of fold and thrust-belts remains under-appreciated. We use a series of balanced cross sections across areas of thin- and thick-skinned tectonics superimposed over former extensional structures in order to characterize the style of deformation, segmentation and displacement magnitude. We detect the style of fault linkage in foothill settings adjacent to inversion belts. The most relevant aspect is the presence of inherited ‘soft linkages’ generating zones of displacement deficit, which in contraction interact laterally with en-echelon inverted segments via ‘detachment linkages’. We document the temporal development and interaction between inverted faults and fault splays branching from them where both are coeval but where the frontal fault tips propagate more slowly during Oligocene and Early Miocene times. Later, during the Neogene, the frontal fault splays slip faster than the main inversion fault. The structural style of thrust-belt development displays along-strike variations, which reflect the changes in sedimentation rates and mechanical conditions of deformation. However, the timing and magnitude of shortening remain uniform along-strike.