Cordón de Lila-Sierra de Almeyda Cambro-Ordovicic batholith: geochemistry of the plutonic rocks. Antofagasta region ,Chile

Abstract

An Upper Cambrian-Ordovician (490-460 Ma) batholith crop out along the Cordón de Lila and Sierra de Almeida, in the Antofagasta region, northern Chile, which belongs to the Famatinian arc. Two plutonic rock types can be distinguished: granodiorites and monzogranites. The first lithology is positioned along an occidental fringe in as much the second is located along an oriental part of the batholith. The main geochemical difference between the two lithologies is the enrichment in silica and K of the second with respect of the first one. Most of the granodiorites are metaluminous or are located between the metaluminous and peraluminous fields. The monzogranites are mostly peraluminous. The chemical composition of the plutons (mayor and trace elements and rare earth elements) allow to infer a common origin for both groups, from a mafic magma that evolved by fractional crystallization. The difference in composition between both lithologies, specially the meta or peraluminous character, can be explained by means a different degree of interaction of the original magma with the felsic crustal rocks.