Deformation style and controlling geodynamic processes at the eastern Guadalquivir foreland basin (Southern Spain)

Abstract

The tectonic structure of the Guadalquivir foreland basin becomes complex eastward evolving from a single depocenter to a compartmented basin. The deformation pattern within the eastern Guadalquivir foreland basin has been characterized by combining seismic reflection profiles, boreholes, and structural field data to output a 3‐D model. High‐dipping NNE‐SSW to NE‐SW trending normal and reverse fault arrays deform the Variscan basement of the basin. These faults generally affect Tortonian sediments, which show syntectonic features sealed by the latest Miocene units. Curved and S‐shaped fault traces are abundant and caused by the linkage of nearby fault segments during lateral fault propagation. Preexisting faults were reactivated either as normal or reverse faults depending on their position within the foreland. At Tortonian time, reverse faults deformed the basin forebulge, while normal faults predominated within the backbulge. Along‐strike variation of the Betic foreland basin geometry is supported by an increasing mechanical coupling of the two plates (Alborán Domain and Variscan basement) toward the eastern part of the cordillera. Thus, subduction would have progressed in the western Betics, while it would have failed in the eastern one. There, the initially subducted Iberian paleomargin (Nevado‐Filábride Complex) was incorporated into the upper plate promoting the transmission of collision‐related compressional stresses into the foreland since the middle Miocene. Nowadays, compression is still active and produces low‐magnitude earthquakes likely linked to NNE‐SSW to NE‐SW preexiting faults reactivated with reverse oblique‐slip kinematics. Seismicity is mostly concentrated around fault tips that are frequently curved in overstepping zones.

Triassic stretching directions in Iberia and North Africa inferred from magnetic fabrics

“…South Demanda fault or Pineda de la Sierra fault; Santana‐Torre, ) faults could explain the deduced stretching direction from K max . In the southern margin of the Iberian Variscan Massif, NE–SW to NNE–SSW basement rooted normal faults deforming Neogene sediments (Marín‐Lechado et al, ) could also be active during the Triassic sedimentation, but their orientation is not coherent with the deduced stretching direction from previous magnetic fabric data in a simple extensional scenario. A more detailed tectonostratigraphic study of the Triassic deposits of this area would be needed to better relate main faults and K max orientations.…”

Seismicity in Strike‐Slip Foreland Faults (Central Betic Cordillera Front): Evidence of Indentation Tectonics

“…In the easternmost Guadalquivir foreland basin, a region holding low seismic hazard (Peláez & López Casado, 2002), two significant swarms have been recorded in this decade: the 2012 and 2013 Torreperogil sequence, and the current northern Guadiana Menor seismic sequence ( Figure 2b), with most earthquakes located 9-13 km deep. The Torreperogil seismic swarm was clearly related to strike-slip basement tectonics, supported by some focal mechanisms, although seismicity data alone do not explain the basement's active fault (Marín-Lechado et al, 2017;Morales et al, 2015;Pedrera et al, 2013;Roldán et al, 2013). The characteristics of the Guadiana Menor seismicity are discussed for the first time in this study.…”

“…In order to highlight the origin and significance of Guadiana Menor seismicity, seismological reprocessed data were combined with new geophysical (gravimetry, electrical resistivity tomography) and geological data. These data were integrated with previous seismic reflection profiles (Marín-Lechado et al, 2017;Roldán et al, 2013) and with gravity data from the TopoIberia project (Ayala et al, 2016; http://info.igme. es/SIGEOF/).…”

“…The geometry of some thick bodies in the Mesozoic basement cover could result not only from olistostromes but also from thrusting. In fact, some studies propose the presence of reverse faults in the basement (Marín-Lechado et al, 2017). The Cazorla Range constitutes a prominent relief above the foreland basin, which suggests recent tectonic activity.…”

“…However, some strike-slip seismic swarms have affected to the Guadalquivir foreland basin (Figure 2), where there are not outcrops of significant strike-slip faults. A seismic series rooted in the area of Torreperogil between 2012 and 2013 has been related with N-S faults (Serrano et al, 2015), with N-S faults that turn E-W in Torreperogil (Morales et al, 2015), and with a combination of E-W transpressive faults related to NE-SW faults (Marín-Lechado et al, 2017;Pedrera et al, 2013). Since 2016, a prolonged seismic sequence has been recorded in the northern Guadiana Menor valley near the village of Peal de Becerro, about 20 km southeast of Torreperogil.…”