Hybridization between I-type and S-type granites in the Ordovician Famatinian magmatic arc, Tafí del Valle, Tucumán, NW Argentina

Abstract

In the Tafí del Valle region, in northwestern Argentina, several intrusive bodies of lower Paleozoic age are emplaced in a low to medium metamorphic grade basement, owing to the Sierras Pampeanas. The plutonic complexes called El Infiernillo, La Ovejería, Loma Pelada and Los Cuartos have been previously included in regional descriptive compilations. In this study, new trace element analyses of these intrusive granitoids are presented and added to the geochemical background in order to constrain the main petrological and geochemical characteristics of the lower Paleozoic magmatism in the Tafí del Valle region.Most of the studied intrusive granitoids show calc-alkaline geochemical signatures and are moderately to strongly peraluminous. They can be grouped into three main groups: 1) La Ovejería and El Infiernillo samples present cotectic evolutions that match those trends traced for Cpx + Pl fractionation and similar to the regional calc-alkaline systems used for comparison, at least in the less evolved tonalites and granodiorites. 2) A second group is composed of some granitoids from Loma Pelada and Los Cuartos plutons, which present very evolved compositions with low percentage of CaO and MgO. These granitoids are placed in the compositional range of S type magmas described in the region, trending to the location of the host rocks with increasing peraluminosity. 3) The third group is comprised by the samples of Loma Pelada and Los Cuartos intrusive units that show intermediate geochemical characteristics between the granitoids from El Infiernillo and La Ovejería and the regional metasedimentary rocks. These could be explained by mingling or mixing of magmas with different geochemical signatures, or by an assimilation process that involves a large contribution of metasedimentary material to the calc-alkaline intrusive magmas.