Geomorphic signature of relief rejuvenation in Sierra Morena (Betic forebulge, Spain): evidence of segmented uplift in a strongly strain-partitioned, tectonic scenario

Abstract. The foreland relief of Alpine orogenic belts is often rejuvenated due to the intraplate propagation of orogenic deformation. Thus, in these long-lived areas, localization of relief rejuvenation may be greatly controlled by reactivation of previous mechanical discontinuities. In this regard, we have explored the relationship among relief rejuvenation pattern and the distribution, geometry and kinematics of faults in a wide sector of the Betics foreland (Sierra Morena, Southern Spain). Specifically, we have focused on the forebulge, a WSW-ENE oriented flexural relief that formed, paired to the Betics foreland basin, in response to orogenic load. For this purpose, we have applied both qualitative and quantitative geomorphological tools, including geomorphic indexes and knickpoints pattern modelling in χ space. We have found that the pattern of relief rejuvenation responds to tectonic activity of two groups of faults that often show evidence of reactivation: overall WSW-ENE faults contributing to both regional NNW-SSE relief segmentation and vertical extrusion of the forebulge, and NW-SE reverse faults associated with an outstanding WSW-ENE topographic segmentation in the west of the study area. In addition, our knickpoint modelling suggests that faults related to the southernmost Sierra Morena mountain front have been particularly active in recent times, although their activity span and the relative uplift that they accommodate differ along the Sierra Morena/foreland basin limit. Knickpoint pattern also suggests a significant reorganization of the analysed drainage basins. The strain partitioning accommodated by the structures involved in relief rejuvenation suggests intraplate propagation of the transpressional deformation reported from the Betics external fold and thrust belt.