La Horqueta Formation: Geochemistry, Isotopic Data, and Provenance Analysis

Abstract

La Horqueta Formation is developed from the Seco de las Peñas River to Agua de la Piedra creek within the San Rafael block and was deposited in a marine environment. It comprises dominantly metasandstones, although metasiltstones, metapelites, and rare metaconglomerates are also present. The base of the succession is not exposed and it is superposed through unconformity by Upper Carboniferous units. La Horqueta Formation is folded and shows cleavage. Provenance analyses based on whole-rock geochemistry and isotope data is the main focus of the work. Whole-rock geochemical data point to a derivation from unrecycled upper continental crust, based mainly on Th/Sc, Zr/Sc, La/Th, and Th/U ratios and rare earth element (REE) patterns (including Eu anomalies). Sc, Cr, and V concentrations and low Th/Sc ratios are indicative of a source slightly less evolved than the average upper continental crust. The εNd values are within the range of variation of data from the Mesoproterozoic Cerro La Ventana Formation, which is part of the basement of the Cuyania terrane outcropping within the San Rafael block. The Rb-Sr whole-rock data indicate that the low-grade metamorphism and folding events are Devonian in age. U-Pb detrital zircon ages suggest main derivation from the Mesoproterozoic (“Grenvillian-age”) basement of the San Rafael block and the Pampean–Brasiliano cycle, as well as a detrital input from the Río de la Plata craton and the Famatinian belt. Despite geochemical similarities, Río Seco de los Castaños Formation display different proportions of detrital zircon ages, when compared to La Horqueta Formation.