Tectonic evolution of the Gibraltar Arc
Flinch, Joan Francese
Bally, Albert W.
Doctor of Philosophy
The Betic Cordillera of Spain and the Moroccan Rif constitute the northern and southern branches of the Gibraltar Arc, which is the western limit of the Alpine-Mediterranean system. The frontal units (i.e. the Guadalquivir Allochton of the Betic Cordillera and the Prerifaine Nappe of Morocco) have in the past been interpreted as olistostromes. Seismic data from the frontal part of the Gibraltar Arc suggest an accretionary complex migrating towards the west from the Western Mediterranean Basin. Seismic data in the Gulf of Cadiz, in the northwestern Atlantic margin of Morocco between Rabat and Tanger and in the Rharb Basin of northern Morocco have been interpreted and compared with field examples from the external Western Rif and the Guadalquivir region of the Betic Cordillera. The structure of the accretionary wedge consists mainly of imbricated thrusts and low-angle extensional detachments. The structures and internal deformation observed are similar to present-day accretionary wedges. Extensional and compressional structures are coeval with the foredeep development. The emplacement and collapse of the wedge were very rapid and occurred during Tortonian and Messinian time. The internal structure of the accretionary wedge is difficult to map since it originated from a deep-water passive margin succession with allochthonous Triassic evaporites and turbiditic wedges (flysch domain). The Prerifaine Nappe and the Guadalquivir Allochthon record several stages of accretion and westward motion of the Alboran domain, providing important constraints for the evolution of the Gibraltar Arc. Frontal accretion is coeval with uplift in the internal domain and back-arc extension in the Alboran region. A detailed sequence stratigraphic analysis of the Supra-Nappe succession has provided insights into the geodynamic evolution of the region and the effect of Pleistocene glacio-eustatic fluctuations.