Magma Mixing, Recharge and Eruption Histories Recorded in Plagioclase Phenocrysts from El Chichón Volcano, Mexico

Abstract

operative throughout the 200 ky history of the El Chicho n magma Consistent core-to-rim decreases of 87 Sr/ 86 Sr ratios and coincident system. increases in Sr concentrations in plagioclase phenocrysts of varying size (>1 cm to 2 mm) are reported from samples of the 1982 and pre-1982 (>200 ka) eruptions of El Chicho n Volcano. Maximum 87 Sr/ 86 Sr ratios of >07054, significantly higher than the wholerock isotopic ratios (>07040-07045), are found in the cores KEY WORDS: El Chicho n Volcano; magma mixing; microdrilling; pla- of plagioclase phenocrysts, and minimum 87 Sr/ 86 Sr ratios of gioclase zonation; recharge magmas >07039 are found near some of the rims. Plagioclase phenocrysts commonly display abrupt fluctuations in An content (up to 25 mol %) that correspond to well-developed dissolution surfaces. The isotopic, textural and compositional characteristics suggest that