UNIDIRECTIONAL SLIP VECTORS IN THE WESTERN BETIC CORDILLERA - IMPLICATIONS FOR THE FORMATION OF THE GIBRALTAR ARC

We have investigated the kinematics of deformation in a sector of the Gibraltar are in SW Spain, by synthesizing lineation data from major f aults. the variation in structural trends, and palaeomagnetically dete rmined vertical-axis rotations. The kinematic data show that transport directions throughout formation of the are were consistently WNW, reg ardless of structural trend, which varies between 050 and 350 in the s tudy area. The data suggest that this part of the Gibraltar are can be explained simply by oblique convergence with a curved indenter. Taken together with other published data it appears likely that the variati on in thrust transport direction within the Betic Cordillera as a whol e may be considerably less than that in the Moroccan part of the are. Unidirectional convergence, combined with the presence of palaeomagnet ic relations, implies either efficient overprinting of old, rotated li neations, and/or a convergence rate that is much greater than the rota tion rate. Also required is a low degree of partitioning in the thrust wedge. The latter probably increases east of the study area, where th e structural trend becomes more oblique to the transport direction, an d major strike-slip faults occur.