Geochemical Evidence for Mantle Origin and Crustal Processes in Volcanic Rocks from Popocatépetl and Surrounding Monogenetic Volcanoes, Central Mexico

Abstract

Elemental, isotopic, and mineral compositions as well as rock textures were examined in samples from Popocatepetl volcano and immediately surrounding monogenetic scoria cones of the Sierra Chichinautzin Volcanic Field, central Mexico. Magma generation is strongly linked to the active subduction regime to the south. Rocks range in composition from basalt to dacite, but Popocatepetl samples are generally more evolved and have mineral compositions and textures consistent with more complicated, multi-stage evolutionary processes. High-Mg calc-alkaline and more alkaline primitive magmas are present in the monogenetic cones. Systematic variations in major and trace element compositions within the monogenetic suite can mostly be explained by polybaric fractional crystallization processes in small and short-lived magmatic systems. In contrast, Popocatepetl stratovolcano has produced homogeneous magma compositions from a shallow, long-lived magma chamber that is periodically replenished by primitive basaltic magmas. The current eruption (1994–present) has produced silicic dome lavas and pumice clasts that display mingling of an evolved dacitic component with an olivine-bearing mafic component. The longevity of the magma chamber hosted in Cretaceous limestones has fostered interaction with these rocks as evidenced by the chemical and isotopic compositions of the different eruptive products, contact-metamorphosed xenoliths, and fumarolic gases. Popocatepetl volcanic products display a considerable range of Sr/Sr (0 70397–0 70463) and eNd (þ6 2 to þ3 0) whereas Pb isotope ratios are relatively homogeneous (Pb/Pb 18 61–18 70; Pb/Pb 15 56–15 60).