NO MOHR! MODELING DEFORMATION AND DIAPIRISM IN RELATIVELY YOUNG SALT TECTONIC SYSTEMS USING CRITICAL STATE THEORY

Kinematic restorations represent a fundamental analytical tool for testing structural interpretations in both industry and academia. However, they are often based purely on geometric line length and area balancing assumptions and rarely yield unique solutions, especially in structurally complex settings such as mobilized evaporite basins. Additionally, as finite deformation and hence structural damage is dependent not only on the final structural geometry but also the stress and strain paths, comprehensive characterization of strain damage requires an understanding of the forces driving deformation. Ideally, restorations would be carried out while keeping a strain “budget”, yet constitutive equations governing deformation mechanics cannot be run in reverse, and thus it is impossible to carry out numerical tasks such as “uncreeping” salt. However, it is possible to evaluate the viability of structural evolution models by creating forward finite element models of restoration sequences constrained within geologically realistic mechanical frameworks. If these geodynamically viable models are coupled with suitable geologic material properties, physical mechanisms such as salt inflation and diapirism and the resultant finite strain magnitudes and geometries of wall rocks may be characterized. In many Paleogene to recent basins (i.e. Atlantic passive margin systems), suprasalt sediments are presumably weak and poorly consolidated, and thus are susceptible to plastic strain and subseismic reservoir damage. In materials such as these, the finite strain history of material will influence its mechanical and hydrodynamic properties in the present day, and thus the ability to reconstruct these finite strain paths could have tremendous implications for testing a range of structural evolution models. In this study, we use forward structural evolution (finite element) models coupled with critical state material models to explore the fundamental driving mechanisms for salt tectonics and salt diapirism and their influence on the temporal and spatial evolution of basin stress and strain conditions.