Comparing the biotite and amphibole single-mineral thermobarometric models: A case study from the Cordillera de San Buenaventura volcanic rocks, Puna plateau of Central Andes (Argentina)

Abstract

We applied a new thermobarometric model based solely on biotite composition to the trachyandesitic to rhyolitic volcanic rocks of the Cordillera de San Buenaventura, a long-lived magma plumbing system (spanning from the Late Miocene to the Holocene) in the Southern Puna plateau (Central Volcanic Zone of the Andean Cordillera). Within these rocks, biotite is a widespread mineral phase found in association with amphibole, as either glomerocrysts, mutual inclusions, or free phenocrysts. This allowed us to compare the biotite-only model with other thermobarometric estimates that rely on amphibole, mineral-melt, and mineral-mineral composition. Our goal was to determine the conditions of formation for biotite and its petrogenetic significance in the evolution of the Cordillera de San Buenaventura magma system. The results indicate that biotite crystallization occurred mainly at middle-to upper-crustal depths (2.1–5.1 kbar) with temperatures below 1000 °C (763–919 °C). The biotite-only T-P estimates for individual lithologies are consistent with those obtained using the amphibole-only model, and this is particularly true for the thermometer. Furthermore, our findings align with the existing petrogenetic models, which suggest extensive fractional crystallization, and with the analyses of mineral textures, that indicates events of magma replenishment. Therefore, our results support the validity of the biotite-only model and its ability to elucidate magmatic processes, including magma differentiation via fractional crystallization, magma ascent and cooling, and magma replenishment and/or mixing events.