Dioritic to granodioritic calc-alkaline magmatism in the Sierra de Comechingones southern tip, Córdoba, Argentina: tracking the Famatinian arc into the Pampean belt

Abstract

The western Argentinian sector of Gondwana has been the focus of several recent studies related to the Famatinian orogeny; however, the geologic history of arc activity in hinterland areas remains poorly understood. We present new data from the Monte Guazú Complex that reveal arc-related magmatism in the Sierras de Córdoba, which we consider part of the Famatinian hinterland. Igneous rocks comprise a diorite unit which includes an amphibole quartz-gabbro/diorite and a tonalite unit comprising amphibole- and biotite-bearing tonalites to minor granodiorites. Both units constitute a medium-K calc-alkaline seriesranging in composition from metaluminous to moderately peraluminous. Trace-element signatures show Ti- and Nb-depletion and strong incompatible element enrichments (large-ion lithophile elements, Pb, Th, U, and light-rare earth elements) relative to normal mid-ocean ridge basalts, suggesting that they formed inan arc setting. U-Pb zircon geochronology constrains magmatism to 455-498 Ma, while weighted mean ages of 474-489 Ma are mostly synchronous with the Famatinian arc beginning. We demonstrate that fractional crystallization of mantle wedge-derived melts controlled the early magmatic evolution, whilecountry rock assimilation and anatectic melt mixing were prevalent in evolved rock members. These results spatially extend the Late Cambrian-Late Ordovician Famatian retro-arc to the southern Sierras de Córdoba.Our findings show that magmatism involved coeval anatexis of host rocks, conversely to previousgeodynamic models. Our data have fundamental implications for Paleozoic tectonic and magmatic processes operating along the western Argentinian sector of Gondwana, demonstrating the importance of crustal reworking and the addition of mantle material in the Famatinian arc inboard sector.