Quaternary tectonic activity of the Carboneras Fault in the La Serrata range (SE Iberia): Geomorphological and chronological constraints

•The Carboneras Fault is among the most active in Iberia•A decline in fault activity after 30.8 ka is suggested•Slip rates averaged ≥ 0.18 mm/yr (dip) and ≥ 1.31 mm/yr (strike) since 110.3 ka•Most recent fault movement could be younger than AD 637•Results be considered in future hazard analyses

The Eastern Betic Shear Zone (EBSZ) in Southern Iberia is known to accommodate part of the 4-5 mm/yr convergence between Africa and Iberia, but its seismic hazard is not sufficiently understood for an accurate risk assessment. One of the main structures of the EBSZ, the left-lateral 150 km-long Carboneras Fault, displays no clear instrumental and historical activity despite being morphologically expressive. Detailed geomorphological mapping, geochronological analysis, and structural observation on the La Serrata segment of the Carboneras Fault were designed to investigate its recent evolution. Quaternary sediments and geomorphic features were targeted and 42 new numerical ages were obtained based on 66 samples (thermoluminescence, U-series, 14C, 10Be). The chronological framework of La Serrata was constructed by combining these numerical ages with a conceptual model previously developed in the region, which assumes that alluvial fan aggradation was produced during cold and dry periods (glacials and stadials), whereas stability and phases of calcrete formation were favored during warm and wetter periods (interglacials and interstadials). The spatial distribution of dated alluvial fans suggests an early phase of uplift that probably occurred between 1 Ma and 56.6 ka in the northeastern portion of the study area, whereas in the southwest sector the main uplift phase occurred later than 110.3 ka. A decline in fault activity would have taken place after 30.8 ka. Vertically offset dated units indicate minimum dip-slip rates of 0.05 mm/yr and 0.18 mm/yr, averaged for the last 1 Ma and the last 110.3 ka, respectively. Deflected channels and associated dated units yield a minimum left-lateral strike-slip rate of 1.31 mm/yr, averaged for the last 110.3 ka. The most recent fault movement of the fault could be younger than AD 637. Our results suggest therefore that the Carboneras Fault is among the fastest in Iberia, and should be considered in future hazard analyses.