Assimilation of granitic xenoliths in the Michoacán-Guanajuato volcanic field: the case of Arócutin, Michoacán, Mexico

Abstract

A granitic xenolith was found in Holocene volcanic breccias from Arócutin village on the southern shore of the Patzcuaro lake, Michoacan State. The volcanic host rock is a clast of basaltic-andesitic composition with phenocrysts of olivine and plagiocolase, and glass and scarce orthopyroxene in the matrix, as well as olivine-hosted Cr-spinels and glass inclusions. Major, trace and REE element patterns are typical of calc-alkaline rocks and resemble “high-Mg” volcanic rocks of Michoacan-Guanajuato Volcanic Field (MGVF), especially the post-1947 lava flows of Parícutin volcano. Temperatures ranging between 965 °C and 1,149 °C and -log ƒO₂ between 6.88 and 7.79 were estimated. Abundance of xenocrysts in the outcrop, extensive partial melting of the granitic xenolith, as well as the compositional variations of glass as a textural component suggest that crustal assimilation phenomena associated to fractional crystallization played an important role in the magmatic system of the Arócutin lavas. We argue that monogenetic volcanism and andesitic lavas of the CVMG are closely related to partial assimilation of shallow crustal basement.