Thermobarometry applied to the long-lived Cordillera de San Buenaventura volcanic complex in Central Andes. Part II: The effect of “liquid” in inverse modelling

Abstract

The Cordillera de San Buenaventura is a long-lived Neogene-to-Holocene multifaceted volcanic system located in the southern sector of the Altiplano Puna (NW Argentina). The erupted products span from mafic to high-SiO₂ rhyolites, all of which are characterized through time from the same primary assemblage made up of Cpx-Opx-Bt-Hbl-Pl-San-Ol-Mag-Ilm. Recent studies highlighted a common line of descent mainly controlled by amphibole + plagioclase fractionation, and a transcrustal magmatic plumbing system comprising discrete magma storage zones. However, the existing characterization of the anatomy of the magmatic plumbing system derives mainly from inverse mineral-melt thermobarometry models applied to a limited number of the presumed “mineral-melt equilibrium pairs” identified through tests based on Mg-Fe partitioning between phases. In this short communication, we show how the signal of such tests could be misleading due to the multifaceted significance of the mineral-liquid equilibrium in a suprasolidus environment, and therefore how it is preferable the coupling with other inverse thermobarometry model based on the mineral chemistry only. Through this approach, we demonstrate here how the Cordillera the San Buenaventura is vertically distributed along the whole crust, but how major phenocryst phases (Cpx, Opx, Bt, Amp) probably crystallized/fractionated in very limited zones of the plumbing system and then travelled as crystal cargo in the ascending residual liquids.