Latest Cretaceous to Miocene deformation events in the eastern Sierra Madre del Sur, Mexico, inferred from the geometry and age of major structures

Abstract

The Cretaceous-Cenozoic major lithologic units and structures of the Sierra Madre del Sur are well known. The Laramide orogeny is generally considered as the cause of the contractile structures, but the details about the migration, kinematics, and intensity of deformation are poorly known. Furthermore, the deformation events responsible for the post-Laramide strike-slip and normal faults have not been identified. In this paper, we document the migration of the deformation events that occurred in southern Mexico from Maastrichtian to Miocene time. We identify different groups of structures representing three successive deformation events, based on the geometry, age, and kinematics of tectonic structures. Deformation migrated from west to east. The first event, corresponding to the Laramide orogeny, occurred during Late Cretaceous time in the Guerrero-Morelos Platform and ended in the middle Eocene in the east within the Veracruz basin. The Oaxacan fault system, which bounds the Acatlan-Oaxacan block to the east, records Laramide shortening. From six structural sections, we interpret the juxtaposition of the Oaxacan complex against the mylonite belt of the Sierra de Juarez, with subsequent uplift of the eastern border of the Oaxacan complex and, finally, the gravitational overriding of the sedimentary cover in a radial centripetal arrangement. The second event produced strike-slip faulting during NE-SW horizontal shortening from Eocene to Oligocene time. The third event produced normal and strike-slip faults, indicating NE-SW horizontal extension during Oligocene-Miocene time. Major structures produced during these three deformation events are roughly distributed in an arcuate pattern bounding the block formed by the Acatlan and Oaxacan complexes. Based on this pattern and the relatively less deformed Mesozoic rocks within the Acatlan-Oaxacan block, we interpret that most of the deformation resulted from the impingement of this block on thinner crustal domains adjoining the block.