Geomorphic signature of segmented relief rejuvenation in the Sierra Morena, Betic forebulge, Spain

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, the localisation of relief rejuvenation may be largely controlled by the reactivation of previous mechanical discontinuities. In this regard, we explored the relationship between the relief rejuvenation pattern and the distribution, geometry, and kinematics of faults in a wide segment of the Betic foreland (Sierra Morena, southern Spain). Specifically, we focused on the forebulge, a WSW–ENE flexural relief that formed, paired to the Betic foreland basin, in response to orogenic load. For this purpose, we applied both qualitative and quantitative geomorphological tools, including geomorphic indices and knickpoint pattern modelling in χ space. We found that the pattern of relief rejuvenation responds to large-scale flexural uplift coupled with the tectonic activity of two groups of faults that often show evidence of reactivation, namely 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 the 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. The knickpoint pattern also suggests a significant reorganisation of the analysed drainage basins. The strain partitioning accommodated by the structures involved in relief rejuvenation suggests the intraplate propagation of the transpressional deformation reported from the Betic external fold and thrust belt.