Navegando por Autor "MARANGOANHA, Bhrenno"

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Geologia, geoquímica e petrologia magnética do magmatismo básico da área de Nova Canadá (PA), Província Carajás
(Universidade Federal do Pará, 2013-08-29) MARANGOANHA, Bhrenno; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506
Through geologic mapping of the Nova Canadá area, was possible to individualize two mafic units, typified for diabase dikes, isotropic, and extensive bodies of amphibolites with nematoblastic and granoblastic textures, outcropping only in the southwestern part of the area. Both units cross-cut granitoids of Xingu Complex and Sapucaia greenstone belts sequence. They are classified as subalkaline tholeiitic basalts. Diabase dikes are divided into three varieties, namely hornblende-gabbronorite, gabbronorite and norite, being the differences between these ones only concerned the modal contents of amphibole, ortho- and clinopyroxene, once petrographically, they don’t show significant differences. They consist of plagioclase, ortho-/clinopyroxene, amphibole, Fe-Ti oxides and olivine; they show a moderate fractional pattern REE and unremarkable negative Eu anomaly. Tectonically, they are related to a continental intraplate environment, and show OIB and E-MORB-types signatures. On the other hand, the amphibolites show a flat REE pattern and an absence of Eu anomaly. They are classified as island arc tholeiites and show N-MORB-type signature. This lithotype includes plagioclase, amphibole, opaque minerals, titanite and biotite as main mineralogical phases. The mineral chemistry shows in the diabases no significant variation between plagioclase core and rim, being classified as labradorite, with rare andesine and bytownite; the amphibole shows a compositional gradation from Fe-hornblende to actinolite with increasing silica. In the amphibolites, the plagioclase shows a wide compositional variation, from oligoclase to bytownite in the foliated rocks; in the amphibolites less/no foliated, there is only sodic andesine. Pyroxene is only found in the diabase dikes and exhibits considerable variation compositional, showing a magnesium content increasing in the cores; the iron and calcium contents increase toward the rims; it is classified as augite, pigeonite (clinopyroxene) and enstatite (orthopyroxene). Diabase dikes have titanomagntite, magnetite and ilmenita as main Fe-Ti oxides. Textural analyses of these oxides allowed identifying five distinct forms of ilmenite in the diabase dikes: trellis ilmenite, sandwich ilmenite, patch ilmenite, individual ilmenite, internal and external composite ilmenite. Texture features suggest that titanomagnetite and individual and external composite ilmenite crystallized in early magmatic stage. During the subsolidus stage, titanomagnetite was transformed by oxidation-exsolution in intergrowths of almost pure magnetite and ilmenite (sandwich, patch, trellis and internal composite ilmenite). Amphibolites have ilmenite as the only Fe-Ti oxide mineral, that occurs as individual ilmenite, and it is always associated to amphibole and titanite. Norites and gabbronorites are characterized by the highest values of the magnetic susceptibility (MS); these varieties exhibit the highest modal opaque minerals content, having primary titanomagnetite as mineralogical phase. Hornblende-gabbronorites exhibit the moderate values of the MS, and amphibolites, the lowest ones. The negative correlation between MS values with modal ferromagnesian contents of the diabases shows that paramagnetic minerals (amphibole and pyroxene) don’t have significant influence in the magnetic behavior in these rocks. In contrast, the positive correlation between these variables, of the amphibolites, suggests these mineral phases are the main responsible for its values of the MS. Geothermobarometric data obtained from titanomagnetite-ilmenite pair in the diabase dikes show temperature and oxygen fugacity conditions (1112°C and -8,85, respectively) close to NNO buffer.
Acesso aberto (Open Access)
Petrologia e evolução crustal da porção central do Domínio Canaã dos Carajás, Província Carajás
(Universidade Federal do Pará, 2018-09-14) MARANGOANHA, Bhrenno; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; 0294264745783506
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).