Volcanic and tectonic evolution of central Mexico: Oligocene to present

Abstract

Based on a synthesis of geochronologic, stratigraphic, and structural data of the volcanic terrains of central Mexico we reconstruct the spatial and temporal relations between the Sierra Madre Occidental (SMO) and the Mexican Volcanic Belt (MVB). An analysis of 520 radiometric ages integrated with the available geological data shows that the migration of volcanism from the NNW trending, dominantly silicic SMO arc to the roughly E-W trending intermediate to mafic MVB arc occurred gradually in response to the progressive development of the Acapulco trench in early to middle Miocene times. During most of the Oligocene the SMO arc developed in a broad NNW trending belt up to the longitude of Mexico City and as far south as the present Acapulco trench. In latest Oligocece and early Miocene times the volcanic front receded about 230 km from the trench while the rest of the arc retained the same location. This change is thought to reflect the progressive development of the present trench, at the site of the former transform boundary between the North America plate and the Chortis block. In middle Miocene times, intermediate to mafic volcanic products were emplaced along a rough E-W trending belt extending also east of Mexico City, while in late Miocene this volcanism assumed a uniform basaltic character and a widespread distribution. The overall orientation of the arc did not change since 16 Ma to the Present although a trenchward shifting of the volcanic front is observed. Based on the overall orientation of the arc and on the dominant composition of the volcanic products, we propose that the MVB began at about 16 Ma, when an intermediate to mafic volcanic arc with a rough E-W orientation start to form. The tectonic evolution of the western and central parts of the MVB is characterized by a middle Miocene phase of transcurent faulting followed by a transtensional to extensional phase between the late Miocene to the present. Deformation is concentrated within a NW-SE trending zone in the western part and in a 50-70 km wide E-W zone in the central part of the MVB. The coincidence between the onset of the MVB and the middle Miocene phase of transcurrent faulting leads us to propose that the NW-SE and E-W transcurrent faults could have provided preferential crustal magma paths, allowing the formation of the MVB with its oblique orientation with respect to the trench.