Magnesium isotopic composition of continental arc andesites and the implications: A case study from the El Laco volcanic complex, Chile

The continental arc andesites of El Laco volcanic complex exhibit slightly heavier Mg isotopes than normal mantle. Moreover, the pyroxene phenocrysts of ELVC andesites exhibit significantly distinct Mg isotopes from both the whole rock and the magnetite crystals, indicating Mg fractionation during the fractional crystallization of the continental arc andesitic system The negative correlation between the δ26Mg and SiO2 contents and positive correlation between δ26Mg and εNd(t) preclude the continental crustal contamination and magma mixing of continental crust-derived felsic melts for the origin of heavy Mg in andesitic lavas.58