Inheritance of Penetrative Basement Anisotropies by Extension-Oblique Faults: Insights From Analogue Experiments

摘要

During rifting, pre-existing penetrative basement fabrics can affect new faults in cover rocks by a mechanism that does not appear to involve reactivation. This subtle form of inheritance can significantly impact fault network architecture in rift basins above laterally variable basement domains with geomechanical anisotropies. Here we use multi-layer, brittle-ductile, crustal-scale analogue experiments to study the influence of penetrative basement anisotropies on fault patterns in the overlying cover during a single phase of orthogonal rifting. The experiments were designed to test whether basement anisotropies, oriented 45 degrees to the extension direction, can lead to the formation of rift faults that are oblique to both the imposed extension direction and basement anisotropies. Our experiments show that a penetrative, vertically layered, mm-wide basement anisotropy creates extension-oblique faults in the overlying cover. We interpret this to arise when local strike-slip kinematics along the interfaces of mechanically contrasting materials in the basement combine with the regional imposed orthogonal extension, creating a transtensional regime. The width and spacing of alternating "strong" and "weak" basement zones interact with rift kinematics, impacting the orientation, kinematics and spacing of new faults in the cover. New insights on the influence of penetrative, pre-existing basement fabrics on localized re-orientation of 3D strain in the cover have implications for understanding complex fault systems in rift basins and transfer zones.