Morphological and structural analysis of the central sector of the Transmexican Volcanic Belt

Abstract

In this paper the post-orogenic evolution of a central sector of the Mexican Volcanic Belt (MVB) in the states of Guanajuato and Michoacan is analyzed. The main structural units are recognized on the basis of a morphological analysis and geological data. Four categories of morphological units were established. These are: 1. Reliefs belonging to geological formations older than MVB and characterized by Laramide orogenic deformation. 2. Pre-MVB planar structural surfaces. 3. Depositional surfaces belonging to sedimentary orvolcanoclastic infilling of post-orogenic tectonic depressions. 4. Surfaces of MVB volcanoes. In this analysis the main morphogenetic stages were recognized ;these were related to tensional tectonic phases and to the main volcanic events. An early tensional tectonic phase is associated with the volcanic activity which formed the pre-Miocene deposits of the Sierra Madre Occidental. A NNW-SSE trending system is dominant during the late Miocene and is related to the "Basin and Range" province of western U. S. A. NW-SE faulting during Pliocene along Californian trends is responsible for the initial volcanic activity of the MVB. Late Pliocene trends are WSW-ENE. The last tensional phase causes N-S and NNE-SSW grabens, as a possible reactivation of "Basin and Range" structures.