Development of a Brittle Triaxial Deformation Zone in the Upper Crust: The Case of the Southern Mesa Central of Mexico

Abstract

AbstractIt is widely accepted that the polymodal fault patterns accommodate triaxial deformation. Multiphase extension and inherited structural fabrics have been counted as common features for the development of polymodal faults in extensional systems. This research documents the development of a polymodal normal fault system in the Mesa Central of Mexico, focusing on the evolution of the deformation field. The fault system comprises NW and NE grabens and N‐S and E‐W faults. These faults affected silicic volcanic rocks in two Oligocene extensional phases. In the Rupelian (~31 Ma), a NW trending domino fault system was formed, associated with fault domain boundaries (transfer or accommodation zones) oriented NW, NE, N‐S, and E‐W. The domino faults tilted the early Rupelian rocks, and the deformation was biaxial with the principal extension NE‐SW. Subsequently, the Rupelian structures were buried by the middle and late Rupelian volcanism. The second extensional phase occurred in the Chattian (after 28 Ma). In this phase, the Rupelian fault domain boundaries acted as faulting zones forming a polymodal fault system in the volcanic cover. The resulting deformation was triaxial with ENE and NNW horizontal principal extensions. From revision of cases in the literature and the deformation documented in the Mesa Central, we propose a general way to form a brittle triaxial deformation zone, requiring (1) the presence of planes of weakness in the upper crust, (2) the deposition of a cover, and (3) a subsequent faulting event reactivating the underlying anisotropies and producing new faults in the cover.