Main controlling factors on oblique extensional deformations in multiphase rift basins: insights from analogue experiments

In order to investigate the influence of pre-existing faults and their angle (α) with different extension directions on oblique extension deformation and sag structure in multiphase rift basins, three sets of analogue experiments were designed based on the similarity theory, including oblique extensional physical simulation experiments with different angles (α), and two sets of physical simulation experiments of oblique extensional and strike-slip deformations. The experiment results showed that: (1) In multiphase rift basins, the angles between the extension direction and pre-existing faults controlled the ratio between the strike-slip component and the dip-slip components, affecting the sag structure. As the angle increased, the dip-slip component and the width of the sag increased. Conversely, when the angle decreased, the sag width decreased. (2) Affected by the distribution of pre-existing faults, the reactivation style of pre-existing faults differed at different evolutionary stages. During the oblique extensional and strike-slip deformation, when the distance between the pre-existing strike-slip fault and the boundary fault was large, the sag showed a single-fault half-graben characteristic. When the distance between them was small, the strike-slip fault also controlled subsidence, and the sag presented a double-fault graben structure. (3) Sag depth and the amplitude of the compression and shear folds controlled by the reactivation of pre-existing boundary faults with multi-directional extension were also influenced by the distance between the faults. As the distance between the pre-existing boundary faults and strike-slip faults increased, the depth of the sag in the extensional-shear zone gradually increased, and the amplitude of the folds in the compressional-shear zone gradually increased. Conversely, the sag depth and fold amplitude decreased.