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; FOLKMAR HAUFF; ARAGON, EUGENIO; D'ERAMO, FERNANDO JAVIER; CONIGLIO, JORGE; PINOTTI, L.; BOFFADOSSI, MARÍA ALEJANDRA; MURATORI, M. EUGENIA; CONIGLIO, JOAQUIN

INTERNATIONAL JOURNAL OF EARTH SCIENCES

SPRINGER

Lugar: Berlin; Año: 2021

1437-3254

In the Comechingones pegmatitic field, central Argentina, leucogranite and pegmatitebodies crop out in a relatively narrow (25 x 10 km) belt, and were emplacedsynkinematically with the main deformational event of the crustal-scale Guacha Corralshear zone during the Early Ordovician (~475 Ma). These leucogranites and pegmatites are geochemically evolved rocks with high silica and alkalis, low Fe2O3,MgO, TiO2 and CaO, and high ASI values. The leucogranites display quite variable Srand Nd isotope compositions (initial 87Sr/86Sr ratios from 0.7048 to 0.7170, and εNdvalues from +2.0 to -3.1), some of which do not overlap with almost any other preFamatinian rock from the Sierras de Córdoba. The major and trace elementgeochemistry and the particular Sr and Nd isotope compositions of the leucogranitesare here explained by the following processes: 1) water-fluxed partial melting ofamphibolites at relatively low P-T conditions generating currently unexposedgranodioritic melts with unradiogenic 87Sr/86Sr ratios and radiogenic εNd values; 2)fractionation of mostly plagioclase and monazite leading to compositions close to theleucogranite melts; and 3) assimilation of metasedimentary rocks with crustal isotopicsignatures, modelled by assimilation and fractional crystallization processes. Themajor, trace and isotope compositions of the pegmatites suggest a derivation frompartial melting of the same metasedimentary protoliths of the Sierras de Córdoba thatwere assimilated by leucogranite melts. We propose a feedback relationship amongdeformation, anatexis, magma evolution and mass transfer in the context of such acrustal-scale shear zone in the foreland of the Famatinian orogen