Crustal architecture and tectonic evolution of the Gulf of Cadiz (SW Iberian margin) at the convergence of the Eurasian and African plates

摘要

The Gulf of Cadiz, located at the southwestern Iberian margin, is characterized by widespread seismicity, compressional and strike-slip fault plane solutions and by a large, elongated positive free-air gravity anomaly, the Gulf of Cadiz Gravity High (GCGH). Multichannel seismic profiles across and along GCGH, together with bathymetric and gravity data, allow us to study in detail the tectonic architecture and crustal structure of the Gulf of Cadiz. The upper shelf and slope of the Gulf of Cadiz includes the main structural domains of the Betic fold and thrust belt. In the middle part of the Gulf, the Paleozoic basement crops out on the shallow Guadalquivir Bank and is associated with the largest signature of the GCGH, whereas toward the outer part of the Gulf, the basement deepens progressively. A large NW-SE normal fault and conjugate NE-SW faults define a prominent basement high associated with the GCGH. Modeling of the GCGH suggests localized crustal thinning of 10 km along the central part of the Gulf of Cadiz, probably generated during the Mesozoic rifting episode between the Iberian and African plates. Concentric wedges of fold and thrust belts and large allochthonous masses were emplaced in the Gulf of Cadiz during the Neogene compressional phase. The final emplacement of these units becomes progressively young from the SE (pre-early Langhian) toward the foreland in the NW (late Tortonian). Seafloor surface ruptures, pockmarks, and submarine landslides provide evidence of active faulting in the Gulf of Cadiz. To accommodate the present-day convergence between the African and Eurasian plates, previously extensional faults have probably been reactivated and inverted at depth, as suggested by the intermediate depth seismicity.