Active tectonics in the Sierra Nevada (Betic Cordillera, SE Spain): Insights from geomorphic indexes and drainage pattern analysis

摘要

The Sierra Nevada of the central Betic Cordillera is a 3000 m-high mountain range surrounded by Neogene-Quaternary sedimentary basins, having been uplifted since Late Miocene times. The southern and western mountain fronts of the Sierra Nevada are fault-bounded, while the northern one is an unconformity between the Neogene-Quaternary sediments of the Guadix-Baza basin and the metamorphic rocks of the Nevado-Filabride complex. We have carried out a geomorphic study by examining drainage patterns and characteristics of mountain fronts in order to reveal areal variations and styles of rock uplift. Mountain front sinuosity (S_(mf)),area-altitude relations (hypsometric curves), and valley floor entrenchment differ significantly between the northern, western, and southern mountain fronts. The lack of important faults along the northern Sierra Nevada mountain front, together with the elevated topographic position of the Guadix-Baza basin (average altitude is around 1100 m), points to similar uplift of both geomorphic units (sierra and basin) in a single large-scale crustal block. The asymmetry factors show systematic asymmetries at both sides of the Lanjaron River, probably due to the presence of an active NNE-SSW oriented antiform in the western Sierra Nevada. Finally, river profiles indicate maximal river entrenchment in the western part of the Sierra Nevada, probably related to the uplift of the footwall of the Padul-Nigiielas fault-system. Therefore, our geomorphic analysis suggests that the western part of the Sierra Nevada is tectonically active by means of a combination of normal faults along the mountain front and NNE-SSW oriented active folds, which, in turn, likely have a gravitational origin related to the exhumation of the footwall of the normal fault-system.