UPLIFT AND A POSSIBLE MOHO OFFSET ACROSS THE DEAD-SEA TRANSFORM

The East Africa rifts and the Red Sea spreading center are characterized by uplifted shoulders and sunken median valleys. The Dead Sea transform, on the northern extension of the Arabian-African plate boundary, has a similar morphological character despite its well-documented strike-slip motion. To understand the "rift" morphology and the crustal structure beneath the transform we compiled a 320 km long gravity and topography profile perpendicular to the Dead Sea transform. The gravity field and the topography in the region surrounding the profile are generally parallel to the trend of the Dead Sea transform, justifying the two-dimensional approximation of the analysis. The gravity profile was modeled using constraints from seismic refraction, borehole and surface geology data. The observed gravity anomaly can be explained by the juxtaposition of two different sedimentary and crustal sections which have been offset by a 105 km left-lateral displacement across the transform boundary, suggesting a step in the depth to Moho. The existence of a significant density anomaly under the median valley is not required by the model. The current elevation of the transform shoulders appears not to be compensated locally. Assuming a state of local isostasy prior to the development of the transform, the magnitude of the uplift in the vicinity of the profile is estimated at 700-900 m, with a half width of 100-125 km. This topography (uplift) can be fitted equally well by models which assume either dynamic support or regional compensation. It is suggested that if the source of the uplift is thermal, it is located within the upper mantle, since there is no requirement for a shallow density anomaly under the rift itself or in the crust nearby. © 1990.