Navegando por Autor "CUNHA, Ingrid Roberta Viana da"

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Petrografia, química mineral e parâmetros de cristalização da suíte Planalto, Província Carajás
(Universidade Federal do Pará, 2015-07-28) CUNHA, Ingrid Roberta Viana da; FEIO, Gilmara Regina Lima; http://lattes.cnpq.br/9344671380219647; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The Planalto Suite is located in the Canaã dos Carajás Domain of the Carajás Province in the southeastern part of the Amazonian Craton. The suite has Neoarchean age (~2.73 Ga), ferroan character and affinity with A-type granites. Magnetic petrology studies allowed the distinction of two groups: (1) Ilmenite granites devoid of magnetite and showing low magnetic susceptibility (MS) values (MS between 0.6247x10-3 and 0.0102x10-3 SI; average of 0.1522x10-3); (2) Magnetite-ilmenite-bearing granites which display comparatively higher but still moderate MS values (between 15.700x10-3 and 0.8036x10-3 SI; average of 5.1717x10-3). Textural evidence indicates that amphibole, ilmenite, titanite, and, in the rocks of Group 2, also magnetite formed during magmatic crystallization. However, titanite chemical composition suggests that it was re-equilibrated by subsolidus processes. The amphibole varies from potassian-hastingsite to chloro-potassian-hastingsite and shows Fe/(Fe+Mg) >0.8. Biotite also shows high Fe/(Fe+Mg) ratios and is classified as annite although relatively enriched in Al compared to the annite end member. Plagioclase porphyroclasts are oligoclase (An25-10) and the grains of the recrystallized matrix display oligoclasic or albitic composition (An9-2). Mineral chemistry, magnetic petrology and whole rock geochemistry indicate that the dominant group 1 granites of the Planalto Suite were formed under reduced conditions below the FMQ buffer. The group 2 granites crystallized under more oxidizing conditions on or slightly above the FMQ buffer. Pressures of 900-700 MPa for the origin and of 500-300 MPa for the emplacement were estimated for the Planalto magmas. Geothermometers suggest initial crystallization temperatures between 900 °C and 830 °C and water content in the magma higher than 4 wt %. The mineralogical comparison between the Planalto Suite and the Archean subalkaline Estrela Granitic Complex of the Carajás Province reveals strong compositional analogies indicating that they were probably formed under similar conditions. The amphibole and biotite compositions of Planalto and Estrela granites are relatively enriched in Al being comparable with those of the Neoarchean Matok Pluton of the Limpopo Belt. They differ using the same criteria of the Proterozoic rapakivi A-type granites. On the other hand, in terms of Fe/(Fe+Mg) ratio, the Planalto and Estrela granites approach the reduced Mesoproterozoic rapakivi granites and the reduced to moderately oxidized Paleoproterozoic granites of, respectively, the Velho Guilherme and Serra dos Carajás suites and differ from the oxidized granites (Jamon Suite) of the Carajás province and also of Matok pluton. It is concluded that the Planalto Suite and similar Neoarchean granites of the Carajás Province differ in mineralogical characteristics and crystallization parameters of some classic examples of A-type granites and, except for its reduced character, they are akin to the Neoarchean Fe-K and Mg-K granitoids of the Limpopo Belt, as exemplified by the Matok granitoids. This indicates that the collisional setting of Carajás and Limpopo exerted strong influence in the nature of the Neoarchean granitoid magmas.
Acesso aberto (Open Access)
Petrologia experimental e química mineral das suítes Neoarqueanas Vila Jussara e Planalto, Província Carajás, Amazônia, Brasil
(Universidade Federal do Pará, 2023-03-20) CUNHA, Ingrid Roberta Viana da; SCAILLET, Bruno; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
In the Carajás Province (CP), during the late stages of the neoarchean (2.75-2.73), in the Sapucaia and Canãa dos Carajás domains granitoids represented by the Vila Jussara and Planalto suites were formed respectively. These suites are metaluminous and have a geochemical affinity with A-type granites and FeO/(FeO+MgO) whole rock ratios that vary from ferroan to magnesian. Chemical-mineralogical studies performed in these neoarchean granites, based on optical microscopy, scanning electronic microscopy, electron microprobe and experimental petrology revealed notable variation between the main mineral phases. Magmatic epidote is a common mineral phase in the reduced, oxidized and magnesian varieties of the Vila Jussara suite, with pistacite contents between 25 and 30% mol. In the Planalto Suite and others neoarchean granites of the CP magmatic epidote is absent. The study of the dissolution kinetics of Archean epidotes of the CP reveals that its formation and stability are directly linked to pressure, temperature and oxygen fugacity conditions, however, its stability is also conditioned by mechanisms of magma rise, emplacement and crystallization, which affected the dissolution intensity of the epidote crystals. Chemical-mineralogical performed on titanites of the Vila Jussara and Planalto Suites and the paleoproterozoic Jamon Suite revealed notable textural and compositional variations. The titanite’s Fe/Al ratios are quite variable in the studied granites, three major titanite groups were distinguished: 1) high Fe/Al ratio (Fe/Al>0.5); 2) moderate Fe/Al ratio (0.5≤Fe/Al≥0.25); and 3) low Fe/Al ratio (Fe/Al<0.25). Furthermore, in general, the obtained data support the major titanite tendency to stabilize under oxidizing conditions, near the nickel-nickel oxide buffer (NNO), however, the occurrence of magmatic titanite in the reduced varieties from the Planalto and Vila Jussara Suites ratifies that its crystallization is possible under conditions near the fayalite-magnetite-quartz buffer (FMQ). Moreover, experimental petrology studies performed on the same neoarchean suites, reveal that the sample MDP-02E, with tonalitic composition, which represents the magnesian oxidized magma from the Vila Jussara suite, exhibits SiO2 content around 60% in the whole rock composition and 61.05% in the experimental glass, while the sample with sienogranitic composition (AMR-116), from the strongly reduced variety of the Planalto Suite, shows SiO2 content of 74.13% in whole rock and 73.17% in glass, pointing out that the initially calibrated experimental conditions approach the natural magmatic conditions. To characterize the crystallization parameters of the tonalitic and sienogranitic magma, nine experiments were performed on the two samples, with the following conditions: pressure ~4 kbar, ƒO2 ~NNO-1.3 (1.3 log unit bellow the NNO buffer) and temperature varying from 850°C to 668°C and water content from 9% to 6% in weight. Experiments with ƒO2 ~NNO+2.4 and temperatures of 800°C to 700°C with similar pressures and water content variations of the reduced experiments were also performed. Subordinately, experiments with pressures of 8 to 2 kbar with variable redox conditions were performed. These experiments show that the tonalite from the Vila Jussara Suite was crystallized at ~4 kbar from a water-rich magma (>5% in weight) in ƒO2 oxidizing conditions, probably between NNO and NNO+1. On the other hand, the experiments performed on the sample with sienogranitic composition from the Planalto Suite show a main paragenesis of Cpx+Fa which substantially diverge from the natural minerals, suggesting that the experiments did not reach the natural conditions.