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Abstract:
Salt tectonics at rifted margins involves intricate interactions between weak, viscous evaporite layers and brittle sedimentary rocks. Geophysical data and geological interpretation offer valuable insights into evaporite structure formation and the average translation rate of evaporite and sediment layers on time scales of several million years and more. However, shorter-term changes in evaporite translation velocity and their impact on deformation of evaporite and sediment cannot be directly observed in natural systems. Here, we employ 2D geodynamic models of lithosphere deformation, evaporite flow and surface processes. In particular, we consider a realistic, stress-dependent and thus highly non-linear rheology of evaporites, which allows for analyzing the interactions between gravitational loading, evaporite flow and sediment deformation in great detail. We find that the oceanward translation velocity of post-salt sediments evolves in a characteristic manner: first rapidly increasing to peak values during approximately 1 million years due to the evaporite's non-linear rheology, before slowing over tens of millions of years as the evaporite layer thins and welds onto the underlying syn-rift sediments. Peak translation velocity primarily depends on the degree of evaporite-related decoupling between pre- and post-salt strata, with the fastest (>20 mm/yr) translation occurring in models with low evaporite viscosity. Our models elucidate the formation of key salt tectonic structures: turtle anticlines in the upslope extensional domain, irregularly spaced collapsed diapirs in the midslope translational domain, and complex diapir structures in the downslope contractional domain. Finally, our models visualize how asymmetric minibasins in the translational and compressional domains interact with adjacent diapirs, forming highly upturned and overturned strata.
