Shear assisted water-fluxed melting and AFC processes in the foreland of the Early Paleozoic Famatinian orogen: petrogenesis of leucogranites and pegmatites from the Sierras de Córdoba, Argentina

HAUFF, FOLKMAR; CONIGLIO, JORGE ENRIQUE; MURATORI, MARÍA EUGENIA; JUNG, STEFAN; D´ERAMO FERNANDO JAVIER; BOFFADOSSI, MARÍA ALEJANDRA; DEMARTIS, MANUEL; ARAGÓN, EUGENIO; PINOTTI, LUCIO P.; CONIGLIO, JOAQUÍN

INTERNATIONAL JOURNAL OF EARTH SCIENCES

SPRINGER

Lugar: Berlin; Año: 2021 vol. 110 p. 2495 - 2517

1437-3254

In the Comechingones pegmatitic field, central Argentina, leucogranite and pegmatite bodies crop out in a relatively narrow (25 x 10 km) belt, and were emplaced synkinematically with themain deformational event of the crustal-scale Guacha Corral shear zone during the EarlyOrdovician (~475 Ma). These leucogranites and pegmatites are geochemically evolved rockswith high silica and alkalis, low Fe2O3, MgO, TiO2 and CaO, and high ASI values. Theleucogranites display quite variable Sr and Nd isotope compositions (initial 87Sr/86 Sr ratios from 0.7048 to 0.7170, and εNd values from +2.0 to -3.1), some of which do not overlap with almost any other pre-Famatinian rock from the Sierras de Córdoba. The major and trace elementgeochemistry and the particular Sr and Nd isotope compositions of the leucogranites are here explained by the following processes: 1) water-fluxed partial melting of amphibolites atrelatively low P-T conditions generating currently unexposed granodioritic melts withunradiogenic 87Sr/86 Sr ratios and radiogenic εNd values; 2) fractionation of mostly plagioclase and monazite leading to compositions close to the leucogranite melts; and 3) assimilation of metasedimentary rocks with crustal isotopic signatures, modelled by assimilation and fractional crystallization processes. The major, trace and isotope compositions of the pegmatites suggest a derivation from partial melting of the same metasedimentary protoliths of the Sierras de Córdoba that were assimilated by leucogranite melts. We propose a feedback relationship amongdeformation, anatexis, magma evolution and mass transfer in the context of such a crustal-scale shear zone in the foreland of the Famatinian orogen.