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Numerical Modeling of Continental Margin Contractional Deep Water Salt Tectonics

Sofie Gradmann, Chris Beaumont, Steven J. Ings, and Markus Albertz
Dalhousie University, Halifax, NS

The deep water regimes of salt tectonic systems on continental margins show a variety of different structures. These include prominent salt nappes such as the Sigsbee Scarp (Gulf of Mexico) or offshore Morocco, foldbelts such as the Perdido Foldbelt (Gulf of Mexico), massive inflated salt such as offshore Angola, or very little deformed toes of slopes. The formation and evolution of these different structures is investigated using 2D finite-element models in which frictional-plastic sediments overly a viscous salt layer. The model comprises a complete passive margin sedimentary sequence to account for the complex dynamical interaction of gravity gliding, shelf progradation and extensional and buttress forces. The model experiments also include flexural isostasy, loading by the overlying water column and a parametric calculation of the effects of pore fluid pressures within the frictional plastic sediments. Model results show that the formation of salt nappes is strongly determined by the subsalt topography and the velocity with which the sediment cover progrades over the salt layer. Contributing factors such as salt and overburden thicknesses, sediment aggradation and progradation rates, as well as post-rift margin tilt and thermal subsidence are examined. Comparison of the structural styles and structural evolution is made with natural examples from case studies of passive margins, e.g. of the Scotian Margin. The results provide an improved understanding of the mechanics of the structures, the conditions leading to the range of observed toe-of-slope salt tectonic structures, and can contribute to the deep water frontier exploration of these regions.