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

DEMARTIS, MANUEL; JUNG, STEFAN; HAUFF, FOLKMAR; ARAGÓN, EUGENIO; D'ERAMO, FERNANDO JAVIER; CONIGLIO, JORGE ENRIQUE; PINOTTI, LUCIO PEDRO; BOFFADOSSI, MARÍA ALEJANDRA; MURATORI, MARÍA EUGENIA; 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, leucograniteand pegmatite bodies crop out in a relatively narrow (25 x 10 km) belt, andwere emplaced synkinematically with the main deformational event of the crustal-scaleGuacha Corral shear zone during the Early Ordovician (~475 Ma). These leucogranitesand pegmatites are geochemically evolved rocks with high silica and alkalis,low Fe2O3, MgO, TiO2 and CaO, and high ASIvalues. The leucogranites display quite variable Sr and Nd isotope compositions(initial 87Sr/86Sr 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 rockfrom the Sierras de Córdoba. The major and trace element geochemistry and theparticular Sr and Nd isotope compositions of the leucogranites are hereexplained by the following processes: 1) water-fluxed partial melting ofamphibolites at relatively low P-T conditions generating currently unexposedgranodioritic melts with unradiogenic 87Sr/86Sr ratiosand radiogenic εNdvalues; 2) fractionation of mostly plagioclase and monazite leading to compositionsclose to the leucogranite melts; and 3) assimilation of metasedimentary rockswith crustal isotopic signatures, modelled by assimilation and fractionalcrystallization processes. The major, trace and isotope compositions of thepegmatites suggest a derivation from partial melting of the samemetasedimentary protoliths of the Sierras de Córdoba that were assimilated byleucogranite melts. We propose a feedback relationship among deformation,anatexis, magma evolution and mass transfer in the context of such acrustal-scale shear zone in the foreland of the Famatinian orogen.