How to Cite
Macgee, J. J., Tilling, R. I., & Duffield, W. A. (1987). PETROLOGIC CHARACTERISTICS OF THE 1982 AND PRE-1982 ERUPTIVE PRODUCTS OF EL CHICHON VOLCANO, CHIAPAS, MEXICO. Geofísica Internacional, 26(1), 85-108. https://doi.org/10.22201/igeof.00167169p.19184.108.40.2060
Petrographic, bulk-chemical, and microprobe studies of a suite of rocks from El Chichón volcano, Chiapas, Mexico, indicate that the juvenile materials of the 1982 and pre-1982 eruptions of the volcano have essentially the same mineralogy and chemistry. Our analytical data suggest that the magmatic products have remained uniform in chemical composition during the approximately 0.3 m.y. represented by the samples. Modally, plagioclase is the dominant phenocryst, followed by amphibole, clinopyroxene, and several minor phases, including anhydrite. The absence of anhydrite from all but one of the pre-1982 samples possibly reflects the effect of post-eruption leaching by meteoric water. Plagioclase phenocrysts are complexly zoned, with pronounced spikes in Ca contents occurring at boundaries between clear and inclusion-rich zones of the plagioclase. These anorthite-rich zones in plagioclase are likely produced by fluctuations in volatile pressure on the magma and may reflect the changes in El Chichón's magma reservoir in response to repetitive, explosive eruptive activity.