Petrologia e evolução crustal da porção central do Domínio Canaã dos Carajás, Província Carajás

Abstract

Geological mapping allied to microstructural, petrological, geochemical, geochronological (Pb-Pb and U-Pb) and isotopic (Nd and Hf) data performed in the central portion of the Canaã dos Carajás domain, Carajás province (Amazonian craton, Brazil) allowed the individualization of new geological units previously grouped into Xingu complex and Plaquê suite, besides the redefinition of the limits from the other units already mapped as well. Therefore, four main events have been described in this portion of the province as follows: (1) in the Mesoarchean, between 3.0 and 2.93 Ga, TTG crust was generated in an N–S subduction setting by partial melting of LILE-enriched basalts (formerly transformed in garnet amphibolite), similar to oceanic plateau basalts; (2) at 2.89–2.84 Ga, in collisional setting, large volume of anatectic granites was formed and contributed to crustal thickening, which triggered granulite-facies high-temperature metamorphism in the TTG crust, forming the felsic granulite from Ouro Verde area; and (3) in the Neoarchean, between 2.75 and 2.73 Ga, this portion of the crust underwent delamination process (detachment from the weak lower crust), promoting generation of enderbitic melt by partial melting of the lower crust (Mesoarchean mafic granulite). This event also promoted partial melting of the upper crust, which generated the Pium diopside-norite magma. The emplacement of this mafic melt into the Mesoarchean basement (felsic granulite) triggered their melting, and generates a leucogranitic melt, which both melts (mafic and felsic) mixed and mingled, then forming the Vila União hybrid granitoids. The emplacement of the mafic (Pium diopside-norite), felsic magmas (leucogranites), and their mixed products (Vila União hybrid granitoids), as well as the enderbitic magmas, was channeled into pre-existing Mesoarchean shear zones trending E– W in the crust (Itacaiúnas shear zone). The generation and consolidation of the Neoarchean magmas occurred in pure shear-dominated transpressional tectonic regime, giving rise to the syn-tectonic nature on these granitoids. This tectonic regime was responsible to the exhumation of the Mesoarchean granulitic crust in a regional imbricated system. Lu- Lu-Hf isotope data of magmatic cores of the zircons from the Mesoarchean felsic granulites from Ouro Verde area show Hf-TDM2 of 3.44–3.15 Ga and εHf(t) values between -1.7 and 3.0, which suggests juvenile source. The Neoarchean enderbite presents Hf-TDM2 of 3.46–3.29 Ga and lower εHf(t) values (between -4.8 and -1.9), and points to a longer crustal residence time to the enderbitic rocks. Hf-isotopic behavior for the Vila União granitoids [Hf-TDM2 between 3.46 and 3.29 Ga, and εHf(t) between -4.6 and -1.8] is quite similar to the enderbites, which the hybrid granitoids Hf-isotopic data are interpreted as being only the felsic end-member (leucogranitic magma) from the mixing system. Such statement is supported by the Ndisotopic data, which confirm the hybrid Neoarchean granitoids evolution from mixing at different proportions of juvenile (mafic end-member – Pium diopside-norite magma) and recycled components (felsic end-member – leucogranitic magma).