Large‐scale mechanical buckle fold development and the initiation of tensile fractures

Abstract

AbstractTensile failure associated with buckle folding is commonly associated to the distribution of outer arc extension but has also been observed on fold limbs. This study investigates whether tensile stresses and associated failure can be explained by the process of buckling under realistic in situ stress conditions. A 2‐D plane strain finite element modeling approach is used to study single‐layer buckle folds with a Maxwell viscoelastic rheology. A variety of material parameters are considered and their influence on the initiation of tensile stresses during the various stages of deformation is analyzed. It is concluded that the buckling process determines the strain distribution within the fold layer but is not solely responsible for the initiation of tensile stresses. The modeling results show that tensile stresses are most dependent on the permeability, viscosity, and overburden thickness. Low permeability (<10−19 m2), high viscosity (≥1021 Pa s), and low overburden pressure can explain tensile failure at the fold hinge. Tensile stresses in the limb of the fold cannot (in general) be explained by buckling. Rather, it develops due to a combination of compression and erosional unloading. The modeling results show that erosion of high permeability rocks can explain the generation of tensile stresses at significant depths (∼2 km) both at the hinge of the fold and throughout the limb of the fold. This study shows that tensile stresses and associated failure within buckle folds is directly dependent on the distribution of material parameters but moreover to the strain history of the geologic system.