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Controls of Shapes and Evolution of Salt Diapirs: Experimental Studies


Experimental models were conducted to study the controls of the evolution and geometry of salt diapirs and the transition from passive to active diapirism. The experiments used both constant and variable sedimentation rates, and different thicknesses of the silicone gel to represent salt. Constant sedimentation rate experiments show that the evolution of diapirs is strongly dependent on the rates of sand deposition and the thickness of the source layer. Low rates of sedimentation and thick source layers result in high rates of flow that leads to cylindrical diapirs that eventually develop flared shapes with overhangs; whereas high sediment rates and thinner source layers result in tapered shapes and eventual eclipse and occlusion of the diapirs. Variable sedimentation rates result in changing shapes of diapirs over time. A small increase in sedimentation rates for flared or cylindrical diapirs result in an initial eclipse followed by tapering and a transition to active diapirism and enables the diapir to pierce the overlying sediments. Subsequently, the narrower diapir returns to passive diapirism. A large increase in sedimentation rates result in a permanent eclipse because the tapered diapir is unable to penetrate the greater thickness of the overburden. Finally, thicker source layers generally show wider diapirs associated with both phases of deformation. The resulting models are directly applicable for the analysis of the geometry and evolution of poor or partially imaged salt diapirs in natural subsurface examples.