Listric Faults: A simple Mohr analysis shows that the increase of the confining pressure (σ3) with depth implies that the angle between newly formed fault planes and σ1 (the principal stress axis, vertical in extensional tectonic regime) progressively increases. Since σ1 remains vertical this means that the dip of the faults decreases with depth. Faults extending deep in the upper crust are not planar but listric. Below, a sandbox experiment of listric faulting, such extensional basins are common in the geological record.
Sandbox models from Ken McClay & Tim Dooley, Fault Dynamics Research Group, Department of Geology, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK.
Reconstruction of a seismic section from the Kwanza Basin, Angola, illustrates the evolution of rafts (fault blocks isolated by extreme extension) above a décollement of salt. The deformation involves various salt diapirs and half-grabens bounded by listric faults. The animation shows structures that are analogous to hydrocarbon-bearing basins in both sides of the South Atlantic, Gulf of Mexico, and Red Sea, among other areas.
Animation from: Guglielmo, G., Jr., D. D. Schultz-Ela and M. P. A Jackson, Raft tectonics in the Kwanza Basin, Angola.
