ALPINE TECTONICS AND ROTATION POLE EVOLUTION OF IBERIA

The geological evolution of the Betic Cordilleras and Pyrenees reflects the Cretaceous and Tertiary rotation pole and kinematic evolution of the Iberian and African plates. New constraints on the Alpine tectonic evolution of the Iberian plate are provided by P-T-t data and regionally consistent stretching lineations from the metamorphic parts of the Betic Cordilleras. High-pressure low-temperature metamorphism in the Betic Cordilleras resulted from continent-continent collision which caused subduction to a maximum depth of 37 km. A preliminary 116 ± 10 Ma radiometric age for this event corresponds to the initiation of seafloor spreading to the west of Iberia which lasted until about 80 Ma. Intracontinental thrusting in the Betics between 99 Ma and 83 Ma took place after subduction ended. E-W to ESE-WNW trending stretching lineations indicate the direction of thrusting, which resulted in extensional strains of 200-600%. The timing of thrusting in the Betics coincides with a 95-80 Ma tectonic phase in northern Africa, during which E-W stretching lineations were formed. The stretching lineations are coincident with the 110-80 Ma motion vector of Africa-Iberia with respect to Eurasia. Thrusting in the Betics and deformation in northern Africa was driven by convergence of Africa-Iberia and Eurasia. Cretaceous deformation is further recorded by terrigeneous sedimentation in the Mauritanian Flysch and by the tectosedimentary evolution of the Malaguide Complex. Crustal thinning, magmatism and metamorphism in the Pyrenees during the 110-85 Ma period is governed by a left-lateral strike-slip of Africa-Iberia with respect to Eurasia around the same rotation pole as thrusting in the Betics. During the 80-54 Ma period the rotation pole was situated west of Gibraltar, near the previous active collision zone. This inhibited large-scale overthrusting and related penetrative deformation in northern Africa and the Betic Cordilleras. Deformation was instead transferred to the northern boundary of Iberia, now acting as an African promontory. From the Campanian on wards, oblique convergence took place around the combined Gibraltar rotation pole. Deformation culminated in the late Eocene, corresponding to spreading in the Norwegian-Greenland Sea at 55 Ma which induced an additional compression in western Eurasia. During the Pyrenean collision, high-pressure metamorphic rocks in the Betic Cordilleras were exhumed and they cooled substantially. The cooling trend was disturbed by Oligocene extensional deformation and introduction of a transient heat source, which correlates with the mantle being uplifted during extension. Heating culminated at the Oligocene-Miocene boundary in the Betic Cordilleras and in northern Africa. This evolution agrees with the development of a plate boundary between Iberia and Africa at 30 Ma, after completion of the Pyrenean collision. The new plate boundary was connected to the western European rift system. Renewal of compression and overthrusting in the Betic Zone took place after 20 Ma. Overthrusting is succeeded by two phases of wrenching, juxtaposing crustal segments with different Moho depths inherited from the late Oligocene to Early Miocene extension. © 1990.