Ferropyrosmalite-bearing fluid inclusions in the North Patagonian Andes metasedimentary basement, Argentina: A record of regional metasomatism

Abstract Quartz segregations in paragneisses from the Paleozoic basement of North Patagonian Andes contain highly saline multiphase fluid inclusions with rare daughter mineral ferropyrosmalite detected by Raman analysis, besides halite, sylvite, hematite, and/or magnetite. During heating experiments, L-V homogenization occurs (256–515 °C), followed halite dissolution (287–556 °C) and at 550–581 °C. The latter phase transition triggers growth clinoamphibole crystals according to following idealized reactions, written for potential end-members: 4 F e 8 S i 6 O 15 [ ( H ) C l ] + a 2 q Ferropyrosmalite ↔ 3 5 22 17 16 − 12 Ferro-actinolite Fe aq 2Al Na Al Si Cl Chloro-hastingsite amphibole resembles composition ferro-actinolite but also has striking similarities chloro-hastingsite, as indicated spectroscopy. experiment, hematite (when present) transforms magnetite uptake H2, whereas without Fe-oxides traces H2 after reaction. This transformation shows that might result retrograde re-equilibration brine, implying Fe2+, Cl–, H2O enrichment Ca2+ brine. Pervasive flow fluid-assisted diffusion are recorded channel way microstructures, healed microfractures, dissolution-reprecipitation phenomena, demonstrated cathodoluminescence microscopy. These alkali- FeCl2-rich brines, derived magmatic sources possible Mesozoic age, were related regional metasomatism, coeval widespread granitoid activity.