3D geodynamic evolution of strike-slip restraining and releasing bends modulated by surface processes: application to the Dead Sea Transform

The region around the Dead Sea Transform represents a unique example of the structures that form around restraining and releasing bends in a strike-slip environment. With our 3D numerical models, we aim to understand the processes that shaped the region including the Dead Sea Basin, the Dead Sea Transform Fault, and the Lebanese Restraining Bend.

In our study, we employ geodynamic modelling using the software ASPECT coupled to the surface processes code FastScape. Our model setup includes a compressive and a tensional stepover along a strike-slip fault with periodic along-strike boundary conditions. Even though we use a simplistic setup with horizontally homogeneous rock layers, we can reproduce many of the present-day features of the Dead Sea Transform region, including the sediment thicknesses in the Dead Sea basin, heat flow patterns, relative topographical height differences, and the general outlines and activity of the main faults along the Dead Sea basin, the Mount Lebanon and Anti Lebanon ranges.

With our models we can investigate the influence of surface processes on the underlying stepover strike-slip tectonics and the resulting crustal-scale flower structures: (1) Along the tensional stepover, the horizontal distance between the bounding faults of the pull-apart basin increases with greater efficiency of surface processes due to an increasing sediment load filling the basin. The sediments hinder the border faults in approaching each other at the surface, thereby enforcing basin-ward fault dip, resulting in wider and deeper basins with greater surface process efficiency. (2) In the uplifted compressive stepover, the erosional efficiency has a direct feedback on the longevity of faults and the rheological state of the crust through its influence on the uplift rate. Elevated erosion-induced uplift rates lead to a connection of the brittle parts of lower and upper crust, because the upper crustal viscous part is moved into a zone of lower temperatures and thus becomes brittle. This drastic change of the underlying rheology manifests in the formation of a new fault, which cuts through the centre of the compressional area. When no erosion is assumed a similar fault is observed in map view, but cross sections reveal that without erosion this fault has a different origin and the flower structure is more complex and more symmetric than for models that include erosion.