By comparing the features observed on Landsat images with the known geological data, a regmatic system that controlled the entire Neogene to Recent structural evolution of the Western Mediterranean area has been recognized. The system consists of two principal conjugated shear trends, reactivating old fractures, the NE‐SW, or Moulouya, and the NW‐SE, or Gafsa. With these, an E‐W trend of prevailing shear character (Gibraltar) and a N‐S trend with mostly tensional movements (Tyrrhenian), are associated. The trends that characterize the system are always present in all the segments of the circum‐Mediterranean chains and continue in the forelands and in the marine areas, although some may prevail. The orientation and the relative movements of the fractures of the system are consistent with the slip‐line field that develops in a plastic‐rigid mobile area, when this is placed between two non parallel converging rigid blocks. The system evolves according to a monoclinic scheme, which is in turn complicated by the variations of the crustal thickness in the deformed zone and by some pre‐existing discontinuities. A progressive migration in time of the major deformations towards the SE is also observed. Mechanisms of intracontinental subduction induced by the shear system are then postulated. The new proposed model may open up new leads for the identification of prospects in the exploration for hydrocarbons, particularly along the orogenic belts.

No abstract

P. Dainelli2, A. Angelucci3, M.A. Arush4, M.M. Cabdulqaadifl, P. Nafissi2, G. PiccoW, E. Robba6. l%e tectonicsedimentary evolution of SWand central Somalia is characterized by two main depositional cycles. The Jirst cycle (Triassic to Early Cretaceous) is characterized by subsiding basins related to aprocess of crustal thinning, and is associated with the separation ofMadagascar from u k k a , between 165 and 121 Ma*. The second cycle, starting in the Late Cretaceous with a regional uncolzformity, is related to the separation and NEward drift of India, at approximately 80 Ma. The folds that U e c t the Jurassic and Early Cretaceous formations of the Lugh-Mandera basin in SWSomalia are the result of a compressive phase connected with dextral transcurrent movements along NE-S W trending fracture zones. These zones are developedparallel to the oceanic system of transform faults, in connection with the change in the stress regime intervening at the shift of the direction ofspreading between thefirst and the second stages of evolution of the Indian Ocean. * Million (106) years ago.