Estratigrafía y deformación extensional en la región San Miguel de Allende-Querétaro, México

Abstract

The study área is located in the boundary of trhee geological provinces: the Sierra Madre Occidental Volcanic Province, the Sierra Madre Oriental, and the Transmexican Volcanic Belt. Based on the stratigraphy and kinemtics of mapped faults, we recognized four deformation events. The first one (D1) was synchronous with the ~E-W Oligocene extension of the southeastern part of the Sierra Madre Occidental Volcanic Province, two transitional events occurred in the middle Miocene (D2) and in the late Miocene (D3) and the most recent event (D4) was synchronous with the ~N-S Pliocene-Recent extension of the Transmexican Volcanic Belt. Between 24 and 16 Ma there were not volcanism nor deformation events, and after middle Miocene, both migrated toward SE. We recognized the La Joya and Ixtla faults as part of a major structure with a N45°E trend that expose basement rocks and was activated several times since Oligocene. This structure parallels the faults of the northern edge of the Chapala-Tula fault system in the segment located between the Penjamillo Graben and Salvatierra. The fault pattern generated during each of the post-Eocene events were controlled by three major fault systems that corresponds to structural boundaries of major geological provinces. El Bajío fault separates the Mesa Central from El Bajio basin, La Joya and Ixtla faults separates the Mesa Central from the Transmexican Volcanic Belt, and the Taxco-San Miguel de Allende fault system separates the Mesa Central from the Sierra Madre Oriental. The later is 35 km wide and has permitted the synchronous movement of normal faults with different orientation, allowing three-dimensional deformation.