Miocene to Recent structural evolution of the Nevado de Toluca volcano region, Central Mexico

Based on aerial photography, satellite imagery, and detailed field work, a geological and structural model of Nevado de Toluca and its surroundings is presented. The Nevado de Toluca volcano is built upon the intersection of three complex fault systems of different age, orientation, and kinematics. These systems from the older to the younger are: (a) The Taxco-Queretaro Fa ult System (NNW-SSE) with clear expression south of the volcano; (b) The Sa n Antonio Fault System (NE-SW) that runs between the San Antonio and Nevado de Toluca volcanoes; and (c) The Tenango Fault System (E-W) located to the east of Nevado de Toluca volcano. Our field data, supported by previous st udies, suggest that these systems have coexisted since the late Miocene. In addition, the stratigraphy, chronology, and kinematics of fault planes poi nt to the existence of at least three main deformation events that have aff ected the region since the late Miocene. During the early Miocene, an exten sional phase with the same deformation style as the Basin and Range tectoni cs of northern Mexico caused the formation of horsts and grabens south of N evado de Toluca and allowed the intrusion of sub-vertical dikes oriented NW -SE and NNW-SSE. During the middle Miocene, a transcurrent episode generate d NE-SW faults that presented two main motions: the first movement was left -lateral with a sigma(3) oriented NW-SE and later turned into normal throug h a counter-clockwise rotation of sigma(3) up to a N-S position. The latest deformation phase started during the late Pliocene and produced oblique ex tension (sigma(3) oriented NE-SW) along E-W-trending faults that later chan ged to pure extension by shifting of sigma(3) to a N-S orientation. These f aults appear to control the late Pleistocene to Holocene monogenetic volcan ism, the flank collapses of Nevado de Toluca volcano and the seismic activi ty of the region. (C) 2000 Elsevier Science B.V. All rights reserved.