Drop-down formation of deep basins along the Dead Sea and other strike-slip fault systems

We address the mechanism of sedimentary basin formation along strike-slip fault systems with 3-D numerical simulations based on a continuum damage rheology model. The formation of these basins is usually explained by a pull-apart mechanism that predicts a rhomb-shaped basin geometry bounded by two longitudinal strike-slip faults and two transverse listric faults. Significant ductile deformation of the lower crust and upper mantle associated with basin growth requires normal or elevated heat flux. The Dead Sea continental transform is associated with some of the larger and unusually deep basins, among which the southern Dead Sea is the deepest. The heat flow in the Dead Sea basin is anomalously low and it is associated with deep seismicity. Moreover, the basin is bounded by deep transverse normal faults rather than the listric faults required by the pull-apart model. Hence, the formation of the basin cannot be explained by the existing pull-apart model. Ben-Avraham and Schubert proposed an alternative conceptual model for the formation of the deepest basin at the southern Dead Sea. They suggested that an isolated block of lithosphere has dropped into the mantle. We simulate the formation of this and other deep basins along the Dead Sea fault and demonstrate that the `drop down' mechanism of the Dead Sea basin formation suggested by Ben-Avraham & Schubert is possible. Density heterogeneities formed in the crust or upper mantle during a previous stage of regional magmatism, drop into the upper mantle when strike-slip faults are created and detach them from the surrounding lithosphere. The simulations indicate that the resulting basin is rhomb-shaped and that with time it grows by the addition of distinct segments to its edges. The proposed mechanism could account for the formation and evolution of large sedimentary basins along other strike-slip fault systems, such as the San Andreas fault and other continental transform faults.