STRUCTURE OF THE DEAD-SEA PULL-APART BASIN FROM GRAVITY ANALYSES

Analyses and modeling of gravity data in the Dead Sea pull-apart basin reveal the geometry of the basin and constrain models for its evoluti on. The basin is located within a valley which defines the Dead Sea tr ansform plate boundary between Africa and Arabia. Three hundred kilome ters of continuous marine gravity data, collected in a lake occupying the northern part of the basin, were integrated with land gravity data from Israel and Jordan to provide coverage to 30 km either side of th e basin. Free-air and variable-density Bouguer anomaly maps, a horizon tal first derivative map of the Bouguer anomaly, and gravity models of profiles across and along the basin were used with existing geologica l and geophysical information to infer the structure of the basin. The basin is a long (132 km), narrow (7-10 km), and deep (less-than-or-eq ual-to 10 km) full graben which is bounded by subvertical faults along its long sides. The Bouguer anomaly along the axis of the basin decre ases gradually from both the northern and southern ends, suggesting th at the basin sags toward the center and is not bounded by faults at it s narrow ends. The surface expression of the basin is wider at its cen ter (less-than-or-equal-to 16 km) and covers the entire width of the t ransform valley due to the presence of shallower blocks that dip towar d the basin. These blocks are interpreted to represent the widening of the basin by a passive collapse of the valley floor as the full grabe n deepened. The collapse was probably facilitated by movement along th e normal faults that bound the transform valley. We present a model in which the geometry of the Dead Sea basin (i.e., full graben with rela tive along-axis symmetry) may be controlled by stretching of the entir e (brittle and ductile) crust along its long axis. There is no evidenc e for the participation of the upper mantle in the deformation of the basin, and the Moho is not significantly elevated. The basin is probab ly close to being isostatically uncompensated, and thermal effects rel ated to stretching are expected to be minimal. The amount of crustal s tretching calculated from this model is 21 km and the stretching facto r is 1. 19. If the rate of crustal stretching is similar to the rate o f relative plate motion (6 mm/yr), the basin should be approximately 3 .5 m.y. old, in accord with geological evidence.