Tectonics of the western Mediterranean

The evolution of the Western Mediterranean takes place between the converging African and Eurasian plates, therefore the motion between them cannot be determined directly. The motion between them is the finite difference between the independent seafloor spreading systems in the Central and North Atlantic Oceans. Primary magnetic anomaly data from the North and Central Atlantic was reexamined. All Late Cretaceous and Cenozoic anomalies (Anomaly 34 - Anomaly 2) were remapped. Fracture zones were remapped using bathymetic maps, topographic profiles from ship tracks, SEASAT altimetry (geoid deflection) data, and SEASAT derived gravity images. Fracture zones were used as the primary control for the determination of rotation parameters. Finite difference solutions were computed between matched anomalies using the newly determined rotation parameters for each ocean with parameters of Pindell et al. (1988) used for Early Cretaceous and Jurassic spreading in the Central Atlantic. The product was a kinematic model describing the motion of Africa with respect to Europe from 175 Ma to the present. The motion of Africa was seen to be much smoother and not marked by the sharp, unusual direction changes that characterized previous work. On a gross scale the motion could be divided into phases that correlated with major geological events, but on a smaller scale it was clear that relative motion between Africa and Eurasia did little more than set very broad boundary conditions within which a variety of geological events occurred. Africa's motion is divisible into several distince phases. From the Jurassic start of seafloor spreading until the Late Cretaceous Quiet Zone (KQZ) the motion between the plates was sinistral strike-slip. During the KQZ, but prior to Anomaly 34 (84 Ma, Campanian) Africa's motion changed to northeasterly directed compression. Shortly after Anomaly 30 (68 Ma), close to the Cretaceous-Tertiary boundary, until after Anomaly 24 (55 Ma, mid-Eocene) there was a period of little relative motion between the two plates. After Anomaly 24 strong relative motion recommenced between Africa and Eurasia. Africa continued on a trajectory between N and NNE until the Middle Miocene (Anomalies 5A - 5D) when motion became directed to the NW. Within the relative motion framework a model for the geological evolution of the Western Mediterranean Sea is evolved. Although the Western Mediterranean is a Neogene phenomena the history of the region prior to this time is also examined, albeit in less detail. Among the major problems for which solutions are suggested is the convergence direction of Iberia with respect to Europe and the reason extension initiated in the Tyrrhenian Sea.