The geometries and kinematics of inverted fault systems: a review of analogue model studies

Abstract

Abstract The geometries and kinematics of 2D inverted extensional fault systems are reviewed using the results of scaled physical models together with case histories from inverted basin fault systems. 2D analogue models of detached terranes, listric, planar, ramp/flat listric and domino arrays of planar faults were constructed from homogeneous sandpacks and from anisotropic sand/mica layers. The models were first extended and then subjected to horizontal compression in order to reactivate the extensional fault systems. Upon extension simple listric faults produce a characteristic roll-over anticline and crestal collapse graben. Inversion of this system produces reactivation of the main detachment with the development of a fault-bounded wedge of syn-extensional strata elevated above regional together with tightening of the crestal collapse graben. New thrust faults initiate from the tips of the crestal collapse extensional faults. Characteristic ‘harpoon’ structures develop associated with the reactivation of the main detachment. Similar inversion architectures were also produced for the planar fault systems. Extension of ramp-flat listric fault systems produces an upper roll-over and crestal collapse graben together with a ramp syncline and lower roll-over and crestal collapse graben. Inversion of this system only reactivates a part of the main detachment producing a hangingwall shortcut fault that bypasses the upper roll-over system. Inversion of domino fault arrays produced characteristic harpoon geometries of the syn-rift wedge together with shortcut faults in the footwalls of the main domino faults. Analysis of the progressive deformation during both extension and inversion has been carried out using marker points embedded in the models. In the analogue models of detached terranes hangingwall collapse during extension occurs along planar to curved shear surfaces, whereas upon inversion, different, lower angle shear trajectories are utilized. In the domino fault arrays more complicated shear paths are observed as a result of the footwall shortcut faults developed during inversion. These results have important implications for the analysis of extensional and inverted terranes and for fault reconstruction and section balancing techniques. The architecture of inverted fault systems developed in the analogue models show striking similarities to the inverted basin geometries found in natural fault systems such as those in the North Sea and South East Asia. Examples from these terranes are compared and contrasted with the results of the analogue models. Conceptual models for inversion kinematics and fault system architectures are presented.