Magma mixing on the Famatinian magmatic arc from northwest Argentina: Example in the Diablillos intrusive complex, southern Puna

Abstract

On the eastern edge of the southern Puna, Inca Viejo range, NW Argentina, outcrops of the Diablillos intrusive complex are composed of a series of calc-alkaline magmatic arc rocks represented by monzogranite, granodiorite, tonalite and diorite. The monzogranite and intermediate rocks contain abundant enclaves and dismembered dikes. Field relationships, petrographic and geochemical studies suggest that the main mechanism of magmatic differentiation of the magmas was by magma mixing and mingling. Rocks of intermediate composition, such as granodiorite and tonalite correspond to a mixing forming process between crustal and mantle-derived magmas. Magma mixing is observable in the field (microgranular mafic enclaves) and evidenced in the geochemical diagrams (magmatic evolution by no-cotectic line), however, a complex magmatic evolution by processes of fractional crystallization and assimilation of country rocks, can not be ruled out. Contact relationships between the different lithological types and enclave-host, suggest that a magma chamber was formed by multiple pulses and was emplaced in middle levels of the continental crust. In a local and regional context, the geochemical affinities and the age of the Diablillos intrusive complex (501±17 Ma, U/Pb on circon) are consistent with the magmatism of the Oire eruptive complex. Magma mixing is one of the main mechanisms intervening in the origin and evolution of lower Paleozoic magmatism in the Famatinian arc, associated to a subduction setting.