Velocity description of deformation. Paper 3: the effects of temperature dependent rheology on extensional basin architecture

Abstract

The results are presented from two-dimensional, transient numerical models which incorporate temperature, rheology, sedimentation and isostasy for finite rift durations. These models are used to address the role of fault growth and resultant basin geometry in the presence of rheological heterogeneity, generated during continental lithospheric extension. The transition between brittle and plastic rheologies, within the yield strength envelope, is used as a constraint on fault development and is found to be sensitive to the temperature perturbations initiated by the rifting process. Numerical results show that during the early stages of extension, cooling across the fault surface by hanging wall advection induces hardening directly below the fault tip. As a consequence the fault surface becomes detached from the brittle/plastic transition in the upper crust. As rifting continues, major basin-forming faults must grow downwards under the tectonic stress field to maintain contact with the transition surface. This increases the surface area of the fault, allowing the basin to cool further, resulting in an increase in flanl uplift and a deepening of the basin. For longer rift durations, thermal advection from lower lithospheric thinning heats up the basin, cancelling out the earlier cooling effect. The architecture of the rift and its sedimentary infill are therefore controlled by the dynamic response of the lithosphere to varying strength controls. The strength of the lithosphere itself is strongly dependent on temperature, pore pressure and strain rate. This type of thermal feedback process is greatest in areas of rapid extension, where greater discontinuities are set up by the rifting process.