Strain pattern within and around denser blocks sinking within Newtonian salt structures

Blocks of dense material, such as anhydrite, entrained in salt structures have been proposed to sink through their host material. Here, we present the results of numerical models that analyse strain patterns within and around initially horizontal anhydrite blocks (viscosity 1021 Pa s) sinking through Newtonian salt with a viscosity of 1017 Pa s. In addition, the influence of the block aspect ratio (thickness to width ratio; AR) is analysed. The model results show that the blocks are folded and marginally sheared to approach streamlined shapes. The effectiveness of this process is a function of the block AR and influences the sinking velocity of the blocks significantly. Final sinking velocities are in the range of ca. 1.7–3.1 mm/a. Around the block in the salt, an array of folds and shear zones develops during block descent, the structure of which is principally the same independent of the block AR. However, the size and development of the structures is a function of the block size. Monitoring of strain magnitudes demonstrates that the salt is subject to extremely high strains with successively changing stress regimes, resulting in closely-spaced zones of high adjacent to low strain. In comparison to the anhydrite blocks, strain magnitudes in the salt are up to one order of magnitude higher.

Research highlights
► Dense anhydrite blocks sink through Newtonian salt driven by gravity.
► Sinking causes folding and shearing of the block and severe deformation of the salt.
► Salt strain comprises high- next to low-strain zones with folds and shear zones.
► Sinking velocity is a function of block mass and deformation and salt deformation.
► Strain magnitudes are much higher in the salt that in the block.