Evidence for fractionation and mixing processes in Las Angosturas Intrusive Complex, Famatina System, Argentina

Abstract

Las Angosturas Intrusive Complex forms the northern segment of the sierra de Narváez, in the Famatina System of north-western Argentina. It consists of Lower Ordovician granitoids whose composition varies from tonalite and leucotonalite to granodiorite and monzogranite, with biotite and hornblende as the main mafic minerals. There remarkable abundance of granodioritic to tonalitic and dioritic to basic enclaves, whose morphology, size and relationships with the are variable is indicative of interactive processes between magmas of differing compositions. Petrographical, mineralogical and chemical studies suggest that the most appropriate mechanism for the evolution of the granitod series is one of differentiation by crystal fractionation, together with a process of mixing, involving the interaction between a granodioritic magma with a basic melt of deep origin. The emplacement of the granitoids produced an active magmatic arc, generally known as the Famatinian arc, and which has similar characteristics to other intrusive complexes of similar age in north-western Argentina.