Evolução magmática e tectônica dos corpos metabásicos no limite entre os complexos Mantiqueira e Juiz de Fora, sudeste de Minas Gerais

Abstract

This thesis deals with metabasic rocks in Mantiqueira and Juiz de Fora complexes, lithostratigraphic units composed by associations of continental and oceanic magmatic arcs of the Riacian-Orosirian developed around Archaean nucleus, which served as basement for sequences of the Neoproterozoic passive margin environment coverage of Andrelândia Group. Components of Ocidental Terrain of Ribeira Belt, Brasiliano Event s reworked portion of the southern portion of São Francisco s Paleocontinent, are units related to its development and fragmentation. The purpose of this thesis was to study occurrences of metabasites in the basement, from which they can either take part, be older or be more recent. Elemental and isotopic geochemical analyzes (Sr-Nd) of 34 and 21 samples, respectively, were performed. Seven samples where geochronological dated by means of U-Pb zircon (LA-ICP-MS). These were classified in relation to the large series of crystallization, separated as low Ti and high Ti, by geochemical signatures and also discriminated in terms of tectonic environments. From seven samples dated to U-Pb were obtained five different concentrations of ages, from crystallization, metamorphism and inheritance. From isotopic geochemistry were obtained seven different concentrations of model ages TDMNd, probably indicating distinct events of mantle extraction. In Mantiqueira Complex predominate high-Ti tholeiites coming from continental intraplate distensive environments. In Juiz de Fora Complex predominate low-Ti, mostly tholeiites, as well as alkaline basalt and calcium-alkaline of more diverse type, associated to convergent and divergent margin and intraplate. As for the Archaean, there are model ages TDMNd in both units and U-Pb age restricted to Mantiqueira Complex, with ages of Neoarchean (ca 2,7 and 2,6 Ga), from crystallization and inheritance, and Mesoarchean (between 2.8 and 3.2 Ga), from inheritance, which indicate the existence of Archaean crust and intracontinental mafic magmatism. Two concentrations of Paleoproterozoic U-Pb ages were recorded, one at the boundary between Rhyacian-Orosirian period (from ca 2.05 Ga) in both units, and another from Orosirian period (ca 1.97 Ga), represented by two samples in Mantiqueira Complex. From Rhyacian-Orosirian, at the Juiz de Fora Complex, there are two samples with IAT and CAB signatures, possibly related to their associations of oceanic arc rocks. From Mantiqueira Complex there are samples with signatures of intraplate environments (post-arc and post-orogenic), which point to a contemporaneousness of distinct tectonic environments, convergent and divergent. However, most of these analyzes are associated with younger model ages ages TDMNd (Stenian-Tonian, and, to a lesser extent, Calymmian and Ectasian) and very rare U-Pb ages. As for the Mantiqueira Complex they are continental intraplate and as for the Juiz de Fora Complex they are of tholeiitic nature (type MORB) and "alkaline basalt". They are related to events of mantle extraction and distensive magmatism, associated with the attempts and the fragmentation of the Paleocontinent and to the deposition of the Andrelândia Group sequences.