Grenvillian basement and Famatinian events of the Sierra de Umango (29°s): a review and new geochronological data

The Sierra de Umango (29°()(),S-68°40'W) was interpreted as part of a northernmost Grenvillian-age rocks of Laurentian-derived terrane, accreted to the southwestern margin of Gondwana. The most important tectono-metamorphic and magmatic processes related to this collision occurred along the N-S trending Famatinian orogen since the Ordovician to Devonian (e.g. Dalla Salda et al., 1992, 1998; Ramos et al., 1998; Astini, 1998; Casquet et al., 2001), overprinting the magmatic and metamorphic rocks already affected by previous Grenvillian history. In this paper we present new U-Pb ages that extends the outcrops of Grenvillian rocks to the north of the well known localities with Mesoproterozoic rocks, and also constrain the age of the subsequent overprinting events. The new ages together with the already existing data, allow us to understand the geological evolution of the Sierra de Vmango in relation to the Lower Paleozoic Famatinian Orogeny.Centro de Investigaciones Geológica

Calymmian (1.50-1.45 Ga) magmatic records in Votuverava and Perau sequences, south-southeastern Brazil: Zircon ages and Nd-Sr isotopic geochemistry

The main aim of this work is to present and discuss the U-Pb zircon ages and Nd-Sr isotopic data from the metabasic rocks that occur within the metamorphosed Votuverava and Perau volcano sedimentary sequences, located in the Apiai Terrane, south-southeastern Brazil. The geochemical pattern of most of these metabasic rocks is similar to those of tholeiitic basalts, suggesting an extensional environment. The U-Pb zircon ages obtained around ca. 1480 Ma characterize an important basic magmatism during the Mesoproterozoic in south-southeastern Brazil. Nd model ages and epsilon(Nd)/epsilon(Sr) signatures suggest the Mesoproterozoic as the main period of mantle/crust differentiation for the crustal precursors of these metabasic rocks. It is quite possible that the Mesoproterozoic extentional events that caused the opening of large sedimentary basins in southern-southeastern Brazil have been underestimated. Possible regional correlations between the Votuverava-Perau basin (PR), the Betara and Agua Clara sequences (PR-SP) and the Serra do Itaberaba Group (SP) demonstrate the magnitude of the extensional process associated with the break-up of the preexisting continental masses. (C) 2011 Elsevier Ltd. All rights reserved