Extrusion and gravity current of a fluid: Implications for salt tectonics

Numerical models of the extrusion and gravity current of a viscous incompressible fluid are studied to determine the shapes of salt structures formed on the Earth’s surface and the velocities of rock salt extrusion and lateral spreading. Two main types of salt extrusion are examined. In the case of active extrusion, salt rises to the surface at a velocity of about 30–35 cm/yr, forming a salt dome about 550 m in height. In the case of passive extrusion, the velocity of salt extrusion from under a newly developing sedimentary minibasin is significantly lower. In the course of its evolution, the salt dome becomes topographically lower and transforms into a broad plateau. The extrusion velocity of salt controls the shape, size, and velocity of its gravity current. The shapes of salt domes modeled in this study agree well with observations. The gravity current velocities in the models vary from 3 m/yr to 60 cm/yr, depending on the proximity to the current orifice. Numerical modeling of salt extrusion and gravity current in various geodynamic settings can be used for a detailed analysis of the geological and geophysical evolution of structures containing salt layers and the related oil and gas fields.