Unidirectional slip vectors in the western Betic Cordillera: implications for the formation of the Gibraltar arc

Abstract

We have investigated the kinematics of deformation in a sector of the Gibraltar arc in SW Spain, by synthesizing lineation data from major faults, the variation in structural trends, and palaeomagnetically determined vertical-axis rotations. The kinematic data show that transport directions throughout formation of the arc were consistently WNW, regardless of structural trend, which varies between 050 and 350 in the study area. The data suggest that this part of the Gibraltar arc can be explained simply by oblique convergence with a curved indenter. Taken together with other published data it appears likely that the variation in thrust transport direction within the Betic Cordillera as a whole may be considerably less than that in the Moroccan part of the arc. Unidirectional convergence, combined with the presence of palaeomagnetic rotations, implies either eYcient overprinting of old, rotated lineations, and/or a convergence rate that is much greater than the rotation rate. Also required is a low degree of partitioning in the thrust wedge. The latter probably increases east of the study area, where the structural trend becomes more oblique to the transport direction, and major strike-slip faults occur.