Silicic magmas in the Michoacán-Guanajuato Volcanic Field: an overview about plumbing systems, crustal storage and genesis processes

Abstract

The origin of silicic rocks in the Michoacán-Guanajuato volcanic field (MGVF) has been understudied since the volcanic field attracted the attention of researchers. Using geochemical, petrological and structural data from the literature, here we propose a model for the origin of silicic magmas. We found that all volcanic rocks known to date in the MGVF can be divided in 40 % andesite, 33 % basaltic andesite, 15 % basalt, 2 % trachybasalt to trachyandesite, and 10 % dacite-rhyolite. The structural systems that deformed the crust in the MGVF are NNW-SSE-oriented normal faults of the Taxco-San Miguel de Allende fault system, developed during the Oligocene, and the Morelia-Acambay fault system consisting of ENE-SSW to E-W sinistral strike-slip faults developed during the Oligocene-Miocene. In addition to bibliographic data, we present a gravimetric-magnetometric model to investigate the characteristics of the local basement where magmas acquire their final silicic composition, and a seismic tomography model to investigate the deep plumbing system that contribute to form the silicic rocks emplaced on the surface. The only report of assimilation experiments we found in the MGVF literature suggest that plagioclase and pyroxene are more easily digested than quartz by hotter magmas. The digestion of these mineral phases has a direct consequence on the generation of dacites and rhyolites. We propose that regardless of the genesis of andesitic melts, such intermediate magmas arrive to the upper-crust and are forced to evolve within local compression zones where they melt the local granitic basement and form crystal mushes. The compositional variability of silicic rocks in the MGVF is a consequence of the variable mixing between the intermediate magmas and the granitic partial melts.