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

• Autores: Sosa, Graciela; Oriolo, Sebastián; Van Den Kerkhof, Alfons; González, Pablo Diego; Olaizola, Ezequiel; Bechis, Florencia
• Año de publicación: 2020
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Ciencias Exactas y Naturales; Ferropyrosmalite Equilibrium; Fluid Inclusions; Raman Spectroscopy; Cathodoluminescence; Fluid-Assisted Diffusion; Dissolution-Reprecipitation; Ciencias Exactas y Naturales
• Institución: Universidad Nacional de Río Negro

Fil: Sosa, Graciela. Geoscience Center, Georg-August-Universität Göttingen, Goldschmidtstrasse. Alemania.
Fil: Oriolo, Sebastián. CONICET‐Universidad de Buenos Aires. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires (IGEBA). Buenos Aires, Argentina.
Fil: Van Den Kerkhof, Alfons. Geoscience Center, Georg-August-Universität Göttingen, Goldschmidtstrasse. Alemania.
Fil: González, Pablo Diego. Universidad Nacional de Río Negro. Instituto de Investigación en Paleobiología y Geología. Río Negro, Argentina.
Fil: Olaizola, Ezequiel. Universidad Nacional de Río Negro. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio. Río Negro, Argentina.
Fil: Bechis, Florencia. Universidad Nacional de Río Negro. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio. Río Negro, Argentina.
Quartz segregations in paragneisses from the Paleozoic basement of the North Patagonian Andes contain highly saline multiphase fluid inclusions with the 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 by halite dissolution (287-556 °C) and the dissolution of ferropyrosmalite at 550-565 °C. The latter phase transition triggers the growth of clinopyroxene or amphibole crystals according to the following idealized reactions, written for the Fe-end-members: (1) 8615[()64] + 32+ (. ) ↔ 326 + 52+(. ) + 4−(. ) + 32 (2) 4Fe8Si6O15[(OH)6Cl4] + 6Ca2+ (aq.) ↔ 3Ca2Fe5Si8O22(OH)2 + 17Fe2+ (aq.) + 16 Cl- (aq.) + 12OH- + 3H2 Ferropyrosmalite Ferroactinolite During the heating experiment, hematite (when present) transforms to magnetite by the uptake of H2, whereas inclusions without Fe-oxides contain traces of H2 after reaction (2), as demonstrated by Raman analysis. These reactions show that ferropyrosmalite might result from the retrograde reequilibration of these minerals with the brine, implying the uptake of Fe2+, Cl- and H2O, and the enrichment of Ca2+ 38 in the brine. Pervasive fluid flow and fluid-assisted diffusion are recorded by channelway microstructures, healed microfractures and dissolution-reprecipitation phenomena, as demonstrated by cathodoluminescence microscopy. These high salinity brines derived from magmatic sources, possibly of Mesozoic age, were related to a regional metasomatic process, coeval with a widespread granitoid activity.
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