Role of strike-slip faults in the Betic-Rifian orogeny

Abstract

A new model for the Betic-Rifian orogeny of the Western Mediterranean (Spain and North Africa) is proposed in which four strike-slip faults play an important role; the faults are not of the same age. Two faults, the left-lateral Jebha fault to the south (in Morocco and principally in the Mediterranean Sea) and the right-lateral North Betic fault (southern Spain) to the north, define the boundaries of the Alboran block (Betic and Rifian internal zones). Final movement along these faults was during the Burdigalian time. Two other faults, the left-lateral Nekor fault (North Africa) to the south of the Jebha fault and the right-lateral Crevillente fault, somewhat to the north of the North Betic fault, define a larger Alboran block (including part of the Betic and Rifian external zones) that was present during the Tortonian. The following sequence of events is proposed: 1. (a) During the Eocene and Oligocene, the African and European plates converged in a N-S sense causing the breakup and overthrusting of the Betic, Rifian and Kabyle internal zones and then the movement towards the WSW of the Alboran block by slip along the Jebha and North Betic faults. 2. (b) By the end of Burdigalian time, movement along the Jebha and North Betic faults ceased. 3. (c) With continued N-S convergence, the Nekor and Crevillente faults, which bound a larger Alboran block, were formed during the mid- and late Miocene. The Arc of Gibraltar (the zone lying between the four major faults) seems to be a result of WSW motion of a crustal block being thrust over external zones. The model proposed adds to the earlier idea that tectogenesis proceeds from the interior to the exterior of an erogenic belt. In the Betic-Rifian orogeny major strike-slip fracture zones shifted to the exterior of the orogenic belt as the orogeny progressed in order to relieve the stress caused by locking of the more internal faults.