Interaction of acid and basic magmas at the emplacement level of Sierra de Varas Pluton (Cordillera de Domeyko, northern Chile)

Abstract

The interaction between basic and acid magmas has been widely recorded in batholiths and plutons from magmatic arcs. The Sierra de Varas Pluton (SVP), a zoned elliptical granitic body emplaced during the Carboniferous-Permian boundary (~300 Ma), and exposed in the north of Chile, shows evidence of synmagmatic interactions with basic magmas during its emplacement: gabbro batches, mafic enclaves and segmented dikes, with chilled and lobated margins, and exchange of xenocrysts with the granitic rock. Thermobarometric data from rocks of the Sierra de Varas Pluton give temperatures of ca. 750°C (amphibole-plagioclase equilibrium) and 0.26-0.36 GPa (total-Al-in-hornblende), pointing to an emplacement level of 7 to 10 km deep. The amphibole thermobarometry from synmagmatic diabasic dikes show temperatures and pressures of 785-840°C and 0.20-0.45 GPa respectively. The evolution from segmented dikes to elliptic enclaves can be explained by mingling of basic magma with the granite host at the emplacement level of the SVP in the upper crust.