Eruptive and magmatic cycles at Fuego de Colima volcano (Mexico)

Abstract

The Fuego de Colima volcano displays a pattern of eruptive cyclicity, characterized by lava flows and/or slow effusions in an open crater alternating with short explosive events. Historical accounts, field investigations and petrological data allow us to refine our understanding of the relationships between recurrent acidic (acidic andesite) and “mafic” (andesitic) products and this eruptive behaviour. The second to last (1818–1913) and present (1913-present day) cycles are instructive in this respect: the short explosive events in 1818 and 1913 correspond to the initial mixing stage of a differentiated magmatic body with a new “mafic” input. Mathematical modeling shows that the pyroclastic products of 1913 result from the mixing between an acidic andesite (61.5% SiO 2) and an olivine andesite (∼56% SiO 2) in various ratios. The final andesite mixture is made of ∼38% basaltic andesite and ∼62% acidic andesite. The long effusive/extrusive phases correspond to the ensuing differentiation stage of the new magmatic body. For example, the 1961 lava flows were derived from the final mixed and homogenized magma after the eruption of 1913 by fractionation of ∼7% plagioclase, ∼9% pyroxene (clinopyroxene + orthopyroxene) and 0.7% titanomagnetite. The fractionation of 11% plagioclase, 9% pyroxene and 1.4% titanomagnetite is required to produce the composition of the 1986 summit lava dome from the same parent. In conclusion, at Fuego de Colima, an eruptive cycle begins with a short, violent explosive event related to a mixing process and continues with a long, effusive phase characterized by magmatic differentiation. This scheme differs from others that have been proposed, which consider that the eruptive cycles end with an explosive event.