Fault-related folds in the southern Pyrenees

摘要

The fault-related folds observed in the south Pyrenean fold and thrust belt are hybrid structures with elements of detachment folding as well as elements of fault bend and fault propagation folding. Fanning growth strata in all the studied case studies indicate progressive limb rotation during deformation, mainly at their initial stages when fold growing mostly controlled the dispersal of syntectonic sediments as a result of higher uplift rates with respect to sedimentation rates. Break thrusts developed in the fold limb of the initial detachment folds to form fault propagation and fault bend geometries. Inversion folds developed at the rift margins. There the geometry of the folds as well as the brittle deformation patterns are controlled by the inherited fault systems, which are not symmetrical with respect to the fold axis. In the absence of previous structures, brittle patterns developed before or at the initial stages of folding by layer-parallel shortening preserving a symmetrical arrangement with respect to the fold axis.