Thrust faults in inverted extensional basins

Abstract

Thrust faults in inverted extensional basins may not exhibit the simple low-angle, ramp-flat thrust trajectories that are characteristic of many foreland fold and thrust belts, but are expected to show more complex geometries controlled by the architecture of the earlier extensional fault system. The results of sandbox analogue models are reviewed as guides to possible thrust fault architectures in contracted extensional basins. High-angle thrust faults and thrust faults with convex-upwards shapes are characteristic of inverted extensional fault systems. Footwall-vergent shortcut thrusts and hangingwall-vergent backthrusts are characteristic of the inversion models. Fault sequences are complex and do not follow simple ‘footwall-nucleating — footwall-vergent’ rules. The architecture of the pre-existing extensional fault system exerts a strong control on the character of thrust faults in inverted basins and must be taken into account when analysing such regions.