The effects of basement ramps on deformation of the Prebetics (Spain): A combined field and analogue modelling study

Abstract

In this study we test whether pre-existing basement faults control deformation in the Prebetic zones of the Betic Cordillera. We focus on an area in the northern part of the Prebetics which is dominated by a transpressional fault system consisting of a NNE–SSW striking fault zone and E–W striking small-scale thrusts. Field observations show that both sets of faults formed in a regional NW–SE to NNW–SSE directed compressional stress field during the Miocene. We propose that the faults formed on top of a basement containing basement ramps overlain by a décollement of Late Triassic evaporites and clays. These basement ramps have either an E–W or NNE–SSW orientation and result from extensional faulting prior to the compressional phase. The style of faulting in the overlying sediments is controlled by the variation in orientation of the pre-existing basement ramps in a uniform stress field. Where the ramps have an E–W orientation small-scale thrusting and folding occurs, where the ramps are oriented NNE–SSW the fault zone acts as an oblique-slip fault. The model was tested by analogue tectonic experiments incorporating a ductile layer, representing the décollement, overlain by a brittle layer representing the overlying sediments. The pre-existing basement ramps were represented by rigid material. The close similarity between the structures produced during the analogue experiments and those observed in the field suggests that pre-existing basement faults exert a major role on deformation of the Prebetics.