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It 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. Key Points: A brittle triaxial deformation area can be formed under a single stress state owing to kinematic interaction among preexisting faultsThe Oligocene extensional system in the Mexican Mesa Central evolved from biaxial domino style to triaxial polymodal faultingThe rupture of the cover in the Mexican Mesa Central produced the triaxial deformation in response to underlying anisotropies' reactivation [ABSTRACT FROM AUTHOR]

The Mesa Central (MC) of Mexico presents a noticeable feature as is the three-dimensional (3D) deformation of Cenozoic volcanic rocks. To figure out when this unusual deformation began, we constructed a geological map at 1:100,000 scale, with detailed stratigraphy, and thirteen new U-Pb ages in the southern MC. The mapped area is dominated by silicic volcanic rocks with ages from ca. 34.4 Ma to ca. 23.5 Ma affected by coeval normal faulting. An angular unconformity evidences a shift in the deformation style that occurred around 30 Ma, from an NW-trending fault system in domino-style to a polymodal fault system, which also temporally coincided with the emplacement of lava dome complexes. The structural and stratigraphic data give new insight for understanding how the polymodal fault system developed in the southern MC, suggesting that the change in the deformation and volcanism regime played an important role. [ABSTRACT FROM AUTHOR]

The Mesa Central of Mexico (MC) is an elevated plateau located 2000 m above sea level in central Mexico, where intrusions outcrop that register the history of exhumation-erosion occurring during the Late Cretaceous-Paleogene. The tectonic history of the region records formation of the Late Cretaceous-Paleogene 'Mexican orogen'; this was followed by extension of the entire region and several plutons were then exhumed. The age and magnitude of the crustal uplift and erosion occurring during exhumation has not been addressed to date. Therefore, this study reports the crystallization and cooling ages of two plutons, the Tesorera Granodiorite and the Comanja Granite, and estimates their emplacement depths. Based on these data, the exhumation age of the Tesorera Granodiorite is estimated to be between ~73 Ma and ~63 Ma at an exhumation rate of ~528 m/m. y. and that of the Comanja Granite is 52 Ma and 48 Ma at an exhumation rate of ~2500 m/m. y. Exhumation-erosion event of the Tesorera Granodiorite was located on the trace of the San Luis-Tepehuanes Fault System and that of the Comanja Granite on the a trace of the El Bajío Fault System. Furthermore, the high exhumation rate in the Comanja Granite suggests that gravitational collapse played an important role during exhumation. [ABSTRACT FROM AUTHOR]

Basement exposed in the Placer de Guadalupe–Plomosas uplift in northern Mexico provides important clues for the geologic evolution of the region. The stratigraphic units form stacked thrust sheets of psammitic and calcareous formations, interlayered with magmatic rock. The eastern calcareous and quartzite formations exhibit structures associated with ductile deformation, whereas the upper stratigraphic units only contain structures formed via younger brittle deformation. Porphyry interlayered in the upper Plomosas Formation has a U-Pb zircon age of 171 ± 1 Ma. This age is consistent with its stratigraphic position, interbedded quartzarenites with a maximum depositional age of ~168 Ma. Granite flakes within the Horquilla Formation are dated at 209 ± 3 Ma, and the La Viñata quartzite exhibits a maximum age of ~193 Ma. The Upper Plomosas Formation correlates well with the arc-related Middle Jurassic Nazas Formation of northeastern Mexico, constituting the first report of a Jurassic continental margin arc outcrop in the ‘Central Mexican Gap zone’. We document Late Norian to Bajocian ages for the stratigraphic units cropping out in the Placer de Guadalupe area. The Jurassic age cluster indicates that the Nazas Arc magmatism in the region occurred during the Late Triassic and ended in the Middle Jurassic times. Permian ages previously assigned to these rocks and the occurrence of a Permo–Triassic deformation event have to be dismissed. [ABSTRACT FROM PUBLISHER]