Thermobarometry applied to the long-lived Cordillera de San Buenaventura volcanic complex in Central Andes. Part I: Supra-solidus phase equilibria modelling

Abstract

The long-lived Neogene-Holocene Cordillera de San Buenaventura (CSB) volcanic system in Southern Puna (NW Argentina), represents a valuable archive of information for the understanding of eruptive behaviors and magma dynamics and to decipher the anatomy of the trans-crustal plumbing system from the depth of the reservoir to the subsurface magmatic plexus. The CSB is characterized by cyclic mafic-intermediate eruptive styles, spanning from lava flows to caldera-forming events with a nearly continuous compositional series of erupted material from basaltic trachyandesites to high-silica rhyolites. For this reason, the CSB has recently been the focus of petrological studies through a general approach integrating textural observation and conventional thermobarometric models. However, due to intrinsic limits of the formulations, conventional models are not able to define either the P-T conditions of the solidus reaction nor the extent of the pre-eruptive supra-solidus environment. Moreover, conventional models cannot reconstruct either the amount or composition of the residual liquids at given pre-eruptive P-T values. Consequently, the published reconstructions and conceptual models that focus on the pre-eruptive state of the magmatic system are poorly constrained. To address this, the application of forward modelling thermobarometry based on the P-T-X pseudosection methods could represent an effective approach to better-constrain the pre-eruptive supra-solidus environment, to independently assess the effectiveness of thermobaric estimates from conventional modelling, and to evaluate if the modelled raw whole-rock composition is representative or not of the relic pre-eruptive magmatic equilibrium.