Navegando por Assunto "Rochas ígneas"

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Alvo Borrachudo, Serra dos Carajás (PA): rochas ígneas ricas em magnetita e apatita com mineralizações de sulfetos associada
(Universidade Federal do Pará, 1996-05-25) FARIAS, Edielma dos Santos; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
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Estudos isotópicos de U-Pb, Lu–Hf e δ18o em zircão: implicações para a petrogênese dos granitos tipo-A paleoproterozóicos da província Carajás – Cráton Amazônico
(Universidade Federal do Pará, 2018-04-05) TEIXEIRA, Mayara Fraeda Barbosa; SANTOS, João Orestes Schneider; http://lattes.cnpq.br/5516771589110657; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
In ca. 1880 Ma an extensive magmatic event generated A-type granites with rapakivi affinity in the Amazonian Craton, especially in the Carajás Province. In this Province these granites are grouped into three main suites according to mineralogy, geochemistry, and state of oxidation of their magmas – Jamon, Velho Guilherme, and Serra dos Carajás – and include also the Gogó da Onça, Seringa, São João, Gradaús, and Rio Branco plutons. The Gogó da Onça Granite (GOG) comprise a stock composed by biotite-amphibole granodiorite, biotiteamphibole monzogranite and amphibole-biotite syenogranite. The GGO crosscut discordantly the Archean country rocks and are not foliated. All Gogó da Onça Granite varieties are metaluminous, ferroan A2-subtype granites with reduced character. The major and trace element behavior suggests that its different facies are related by fractional crystallization. Zircon and titanite U–Pb SHRIMP ages show that the pluton crystallized at ~1880-1870 Ma. This is more akin to the Serra dos Carajás Suite and to the Seringa and São João granites of Carajás and to the Mesoproterozoic Sherman granite of USA and the Paleoproterozoic Suomenniemi Batholith of Finland. New U-Pb SHRIMP data for the Serra dos Carajás, Velho Guilherme and Jamon Suite and for Seringa and São João Granite show that these plutons crystallized between 1880 Ma to 1857 Ma. Some granites of the Velho Guilherme and Jamon suites and of the Seringa Granite presented 1920 to 1900 m. y. old zircon and titanite crystals interpreted here as antecrysts from an earlier pulse of magma that were incorporated in the main later pulse of 1880 Ma. We also obtained ages of 1865 Ma to 1857 Ma in the leucogranite facies of the Redenção and Bannach plutons, which indicate that the leucogranites of these plutons are younger than their ~1880 Ma old granites and were generated by independent magma pulses that are not cogenetic with the less evolved facies of the respective plutons. Besides it, an age of 1732 ± 6 Ma obtained in the leucogranite facies of the Antônio Vicente pluton of the Velho Guilherme Suite that could represent a magmatic event in the Xingu Region not yet reported or, eventually, could correspond to an isolate hydrothermal event that allowed the growth of zircons. This ranites have been also analysed by Lu–Hf and Oxygen isotopes and few granites also by Nd isotopes. Zircons from all the granites have remarkably restricted initial 176Hf/177Hf (0.281156 and 0.281384) and strongly negative εHf(t) values ranging from –9 to -18, and δ18O fairly homogeneous varying from 5.50‰ to 7.00‰. Small differences were observed internally in the plutons or between them. The ƐHf(t) values of the analysed plutons are strongly negative and similar to Nd isotopic data. The Serra dos Carajás Suite has ƐHf(t) values of -14 to -15.5, the Jamon Suite of -9.5 to -15 and values of -12 to -15 for the Velho Guilherme Suite, while São João, Seringa and Gogó da Onça granites have stronger negative values (ƐHf(t)= -12 to -18). Crustal model ages indicate a Paleoarchean source (3.3 Ga to 3.6 Ga) with a minor contribution from Mesoarchean (3.0 Ga to 3.2 Ga) melts for these granites. This model ages are older than the exposed Archean country rocks of the Orosirian granites of the Carajás Province and more investigation is needed to verify the real existence of that older Archean crust. The studied samples have Hf– O isotopic compositions that overlap within error, and evidence of contamination (crustal assimilation or mixing) of a mantle-derived magma cannot be seen. These plutons crystallized from magmas generated by melting of pre-existing igneous rocks with possibly in the Velho Guilherme Suite a minor contribution from a supracrustal (metasedimentary) component. The Nd, Hf, and O isotope compositions of the Paleoproterozoic granites of Carajás Province clearly attest to an igneous ancient crustal source in the origin of their magmas. The differences observed can result for contrasts in the crustal domains of the Carajás Province that were the source of the granites or of local contamination processes.
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Geologia, geoquímica isotópica e aspectos metalogenéticos das rochas ígneas e mineralizações auríferas associadas - Região de Monte do Carmo - TO
(Universidade Federal do Pará, 1996-12-27) SACHETT, Cleris Regina; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645
The region of Monte do Carmo is located in the middle east portion of the Tocantins state and comprises in its geologic view, rocks from the Lajeado Granite, acid volcanics, metasediments of the Natividade Group and sediments of Phanerozoic age. It consists yet of quartz veins gold bearing mineralizations with several associated sulfides cross-cutting the Lajeado Granite, the volcanics and the metasediments of the Natividade Group. Acid volcanic rocks represented by rhyolite, dacites, rhyodacites and acid pyroclastics occur in the northern part of the Monte do Carmo town. This unity was analised by the Pb-Pb method with zircons vaporization, from which was obtained an age of 2138±11 Ma (2a), also interpreted as the crystallization epoch. The Lajeado Granite, which readly outcrops in the south region of Monte do Carmo, consists of granites, granophyres, as well as amphibole bearing gravite and subordinated leucogranite. Zircons from this body were analysed through the Pb-Pb method and provided an age of 2025±26 Ma (2a). This result was interpreted as the crystallization epoch of the Lajeado Granite inasmuch as the analised samples carne from non-deformed portions of the grafite. These two unities are seccionated by metric shear zones, commonly orientated in the N-S direction, with auriferous quartz veins and sulfide mineralizations. Markable mineralogical and textural transformations of the minerais occur in the wall rock. Samples from these phylonites were analysed through the Rb-Sr method and provided an age of 565±43 Ma (2a). On the basis of regional geologic data, which show the existence of magmatism and tectonism during this period, as well as an intense transformation on the analised rocks, this result was interpretated as the epoch of rocks transformation. Thus, the epochs of the shear zones development and related mineralizations were determined. Within the associated sulfide mineralizations are galena and pyrite. These sulfides were analised through the Pb-Pb method in minerais and yielded the isotopic compositions compatible with an Upper Proterozoic evolution from sources of the Lower Proterozoic. The microthermometric analyses of the quartz veins related inclusions revealed the existence of two kinds of fluids. An aqueous-carbonic fluid with low salinity was trapped in the earliest stages of formation of the veins in a temperature between 250 and 350°C and pressure of 2-3 Kb. With the evolvement of the shear zones, the fluids became more aqueous and more saline (22% weight NaC1), with the existence of the Na and Ca cations that were trapped in the temperatures between 150 and 200°C. In the Morro Lajeado arca localized 10 Km from the Porto Nacional town, small tonalitic bodies occur intrusives in the volcano-sedimentary sequence. Zircon from these granitoids also underwent Pb-Pb analyses, from which was obtained an age of 2069 ± 76 Ma (2a). These analyses however did not yield a well defined plateau, and some ages were much superiors than the average age 2538 ± 207 Ma (2a), what leads to consider this result as a minimum crystallization age to the Granitoid Torres.
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Química mineral e condições de cristalização do granito Gradaús, sul do Pará, Província Carajás.
(Universidade Federal do Pará, 2019-10-04) NERY, Paulo Hiago de Souza; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281
The Gradaús Granite (1882±9 Ma) is part of the intense anorogenic granitic magmatism that occurred during the paleoproterozoic in Carajás Province. It has a rounded shape, with about 800 km² of outcrop area, and is intrusive in metassediments of the Rio Fresco Group. It is composed of five petrographic facies with varying mafic content and texture. The amphiboles are calcic, predominantly Fe-edenites with Fet/(Fet+Mg) ratios between 0.77 and 0.9; hastingsites and Fe-hornblendes occurs subordinately. Biotite is ferrous, with compositions close to the annite pole, with Fet/(Fet+Mg) ratios between 0.81 and 0.96. Based on the aluminum content in the amphibole the emplacement pressure of the pluton was estimated at 240 e 360 MPa. Temperature estimates obtained from the zirconium saturation geothermometer, interpreted as close to the beginning of crystallization, ranged from 780 to 870 °C, while those near the solidus obtained from the amphibole geothermometer ranged from 700 to 750 °C. Amphiboles with high Fet/(Fet+Mg) ratios, the presence of ilmenite> magnetite and the absence of magmatic titanite indicate that Gradaús pluton crystallized under reduced conditions, probably between NNO and FMQ buffers. Biotites show alkaline-subalkaline compositions and always plot in A-type granite fields. Comparative data on mineral chemistry and crystallization conditions with other anorogenic granites from Carajás Province indicate, according to recent studies, that Gradaús Granite has greater similarities to the Serra dos Carajás Suite granites.
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Química mineral e parâmetros de cristalização do Granito tipo A Paleoproterozoico Bannach, Província Carajás, Pará
(Universidade Federal do Pará, 2017-05-30) MESQUITA, Caio José Soares; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The A-type Paleoproterozoic Bannach granite belongs to the Jamon Suíte and cross-cut the Archean units of the Rio Maria Domain in the Carajás Province of the Amazon Craton. It comprises eight facies with varied mafic content.and texture. The dominant amphibole is Fe-hornblende in the more mafic facies and Fe-edenite or hastingsite in the more felsic ones with Fe/(Fe+Mg) ratios of 0.53 to 0.81. In the facies with higher mafic content, it also occurs cummingtonite or grunerite originated from the destabilization of clinopyroxene, with Fe/(Fe+Mg) ratio around 0.50. The biotite is ferroan with Fe/(Fe+Mg) ratio varying between 0.62 and 0.80 except in the late-emplaced medium-grained leucomonzogranites, where it varies from 0.89 to 0.91 and approaches annite in composition. The plagioclase shows normal zoning with sodic andesine or calcic oligoclase cores varying to sodic oligoclase in the more mafic facies and calcic or sodic oligoclase cores and albite borders in the more felsic varieties. The titanite displays Fe/Al ratios similar to those of plutonic magmatic rocks with quartz. Magnetite and ilmenite are significant accessory minerals in all facies. Trellis, composite, individual and patch textural varieties of ilmenite were identified, whereas magnetite occurs in intergrowths with trellis ilmenite, associated with composite ilmenite and in homogeneous crystals associated with cummingtonite-grunerite. There is no significant contrast in composition in the textural varieties of ilmenite, however the ilmenites found in the more felsic granites are enriched in MnO compared to the less evolved ones. The magnetite is always poor in TiO2 and almost Ti-free in the homogeneous crystals. The near liquidus temperatures obtained from the zircon geothermometer vary between 943°C and 795°C, whereas the near solidus temperatures indicated by the amphibole-plagioclase geothermometer are of 807°C to 732 °C, decreasing in both cases from the more mafic to the more felsic granites. The Al-in geobarometer indicated pressures of 300±100 MPa (~11.1±1,9 km) for the emplacement of the Bannach pluton. The Fe/(Fe+Mg) ratios of amphibole and the occurrence of magmatic magnetite and titanite indicate that most granite facies crystallized at moderately oxidizing conditions, however, the biotite compositions indicate for conditions a little more reductive to those of the Jamon magma and the anorogenic granites of the series magnetite of Laurentia. Based on this, it was inferred that the crystallization of the dominant facies in the Bannach Granite occurred under conditions of oxygen fugacity corresponding to those of NNO to NNO -0.5. The late-emplaced medium-grained leucomonzogranites facies is an exception because it displays extremely high Fe/(Fe+Mg) ratios in biotite and approaches the reduced granites of Carajás Province and the ilmenite series granites of Laurentia and Fennoscandia in this regard. This indicates that it crystallized from a magma derived from a more reduced source compared to that of the dominant facies of the Bannach pluton.