Thermodynamic constraints on crustal basement metapelitic migmatite xenoliths entrained in Miocene Ramadas rhyolites (NW Argentina)

Abstract

This study documents the diffuse occurrence of metapelitic migmatite xenoliths within the early-phase proximal eruptive facies of the rhyolitic Miocene Corte Blanco Tuff from the Ramadas volcanic center (Altiplano Puna, NW Argentina). An integrated approach combining field and petrographic observations, microtextural analyses, and mineral and bulk chemical investigations, is developed to describe the biotite-muscovite-rich schlieren (paleosome/protolith) and the leucogranite (leucosome) components of this schlieren-type diatexite migmatite. Major-element mass balance modelling is applied to assess the paleosome-leucosome relationship and estimate the degree of partial melting (up to ca. 30 wt%). Forward modelling thermobarometry using P-T-X constrains the pressure-temperature conditions (0.45-0.60 GPa at 650-700 °C) under which the anatexis occurred via biotite-muscovite-dehydration melting reactions. The thermodynamic results are discussed in the context of both the Altiplano Puna Paleozoic crystalline basement and the shallow crust (<0.2 GPa) magmatic plumbing system of the Miocene Ramadas volcanic center.