STRIKE-SLIP FAULTS IN A RIFT AREA - A TRANSECT IN THE AFAR TRIANGLE, EAST-AFRICA

The Afar Triangle, a diffuse triple junction where the Red Sea, Ethiop ian and Gulf of Aden rifts converge, is examined along an E-W cross se ction in order to recognize traces of strike-slip faulting summarily k nown from earlier studies. Both field evidences from slickensides and airphotograph or satellite image data indicate that strike-slip faults , although less numerous than normal ones, occur throughout this area. These faults mainly strike parallel or at small angles relative to ri fting axes, rather than transversal to them as would be expected if th ey were transforms. Strike slip subparallel to rifts is explained thro ugh lateral displacement between the major lithospheric plates around the junction or, subordinately, by a domino fault mechanism in zones o f diffuse transform deformation. Faults at small angles with the rift axes often constitute conjugate systems suggesting along-axis compress ion, which is considered to be frequently induced by the lateral intra plate shift mentioned above. In other cases, this compression may deve lop in intervals between mantle plumes wedging up along a rift, or at the head of a propagating rift. The main lateral displacements among t he boundary lithospheric plates during the last million of years are s upposed to have been sinistral. This does not challenge the notion of mainly divergent plate movements, but adds to this divergence an antic lockwise shift of the plates around the junction.