Evaluación geológica de los modelos para el truncamiento cenozoico del sur de México: Erosión por subducción y detachment del bloque Chortís

Abstract

The subduction erosion model recently proposed as an explanation for the Cenozoic truncation of southern Mexico is confronted with the traditional model by detachment of the Chortís block. The Chortís block detachment model has some objections previously recognized. In this work, the main objections arisen from the geometric array of the Polochic-Motagua fault system are resolved with a relative left lateral slip of ca. 120 km between the Chiapas Massif and the Polochic-Motagua system, along a southeasterly trend. Such displacement is inferred from the active shear deformation on the Chiapas region and from structural features on the platform of the Gulf of Tehuantepec.

On the basis of the geologic record of southern Mexico, with emphasis on mesozoic basins, as well as on the Chortís block stratigraphic record, the model of Cenozoic tectonic truncation of southern Mexico by detachment of Chortís block and its transference to the Caribbean plate is favored. We discard subduction erosion as the process that trimmed southern México, because its invocation implies a subduction erosion rate of 823.5 km3/m.y./km, a rate 20 times greater than the fast subduction erosion presently occurring. Detachment of the Chortís block remains as the more plausible model for the Cenozoic tectonic reduction of southern Mexico.