Petrology and geochemistry of el Chichón and Tacaná: two active, yet contrasting mexican volcanoes

Abstract

El Chichón and Tacaná have been widely considered subduction-related volcanoes, although they show differences in mineral assemblage and magma composition. El Chichón emitted potassium- and sulfur-rich trachyandesites and trachybasalts during its eruptive history, whereas Tacaná erupted basalts to dacites with moderate potassium contents, and minor high-Ti magmas. The magmatic evolution in both volcanoes involved similar fractionating assemblages of Fe-Ti oxides, olivine, plagioclase, pyroxenes, amphibole and apatite. Both K2O/P2O5 ratios and isotopic signatures, indicate that the melts of El Chichón and Tacaná experienced significant crustal contamination. Magma genesis for both volcanoes has been related to the northeastward subduction of the Cocos Plate. Even if such origin agrees with the location of Tacaná, situated 100 km above the Cocos Benioff Zone, a subduction origin is at odds with recent tectonic and geophysical data obtained for southern Mexico for El Chichón, located about 400 km from the trench. In this chapter we review the existing petrographic and geochemical data for El Chichón and Tacaná volcanoes, in order to understand their magma genesis and evolution.