Impact of inconsistent density scaling on physical analogue models of continental margin scale salt tectonics

Abstract

[1] The influence of inaccuracies in density scaling on the structural evolution of physical analogue experiments of salt systems has been debated, and is here investigated considering a gravity spreading example. Plane strain finite element numerical analysis was used to systematically evaluate the impact of changes in density scaling on buoyancy force, sediment strength, and pressure gradient. A range of densities typical of natural systems (including compacting sediment) and physical analogue experiments was included. A fundamental shift in the structure of the salt-sediment system, from diapir-minibasin pairs to expulsion rollover, was observed when sediment and salt densities were altered from values typical of physical experiments (1600 and 990 kg/m 3 ) to those most often found in nature (1900-2300 and 2150 kg/m 3 ). Experiments equivalent to physical analogue models but with reduced sediment density showed diapir-minibasin pair geometry, persisting to sediment densities of $1300 kg/m 3 . Salt burial by pre-kinematic sediments was found to suppress diapir formation for thicknesses greater than $750 m (0.75 cm at the laboratory scale). The relative importance of disproportionately high buoyancy force, low sediment strength, and pressure gradient in physical experiments was investigated by isolating each of these scaling errors in turn. Buoyancy was found to be most influential in the development of diapir-minibasin pairs versus expulsion rollover geometry. Finally, we demonstrate that dry physical analogue experiments with sediment density reduced to $1140 kg/m 3 (achievable through mixing with hollow glass beads) would provide a reasonable approximation of submarine salt systems in nature (including water load and hydrostatic pore fluid pressure).Citation: Allen, J., and C. Beaumont (2012), Impact of inconsistent density scaling on physical analogue models of continental margin scale salt tectonics,

Numerical modelling study of mechanisms of mid‐basin salt canopy evolution and their potential applications to the Northwestern Gulf of Mexico

“…These experiments, however, employ a very large density contrast of 700 kg m À3 between salt and sediments, thereby making the salt very buoyant. Such density contrasts, much larger than an already fairly high salt-carbonate density contrast, are not realistic (Allen & Beaumont 2012). In model ER1, salt only remains at a structurally higher (allochthonous) level where located above the basement high.…”

Analogue model of gravity driven deformation in the salt tectonics zone of northeastern Mexico

“…Isostatic compensation and thermal subsidence of the underlying lithosphere were not considered. Several authors have pointed out that when using low density silicone putties density scale is not properly considered (Vendeville, 2005;Brun and Fort, 2004;Allen and Beaumont, 2012). Allen and Beaumont (2012) have further pointed out that the buoyancy contrast can provoke some diapirs to appear in the model.…”

“…Several authors have pointed out that when using low density silicone putties density scale is not properly considered (Vendeville, 2005;Brun and Fort, 2004;Allen and Beaumont, 2012). Allen and Beaumont (2012) have further pointed out that the buoyancy contrast can provoke some diapirs to appear in the model. However, the same authors also consider that the setup using SGM36 and sand is suitable for modeling salt tectonics in a submarine environment and that a pre-kinematic layer prevents formation of diapirs.…”

Factors controlling early stage salt tectonics at rifted continental margins and their thermal consequences

“…Although analogue models [e.g., Ge et al ., ] have been successful in reproducing gravitationally driven spreading or glide of salt tectonic systems, important features of rifted margins are difficult to reproduce in physical experiments, namely, compaction of the sedimentary overburden, syntectonic and thermal subsidence of the lithosphere, and flexural response to water and sediment loading. Also, the accuracy of scaling of mechanical material properties with respect to natural systems is debated [ Allen and Beaumont , ], and the lack of materials with suitable thermal properties precludes physical thermal‐mechanical models. The models presented in this study incorporate all of these processes and allow tracking the transient thermal regimes as the salt bodies evolve.…”