Navegando por Autor "TEIXEIRA, Mayara Fraeda Barbosa"

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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, petrografia e geoquímica dos granitóides arqueanos de Sapucaia - Província Carajás-PA
(Universidade Federal do Pará, 2013) TEIXEIRA, Mayara Fraeda Barbosa; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
Geological mapping performed in the eastern portion of the Transition Subdomain, Carajás Province, southern of Canaã dos Carajás and the northern of Sapucaia cities, allowed the identification, individualization and characterization of a variety of Archean rocks, previously encompassed in the Xingu Complex. The oldest unit identified in this area is a hornblende tonalite, correlated to São Carlos Tonalite (~2.93 Ga), which is exposed as blocks or outcrop and commonly present foliation (NW-SE to E-W) or homogeneous aspect. Its geochemical signatures differ from the typical Archean tonalite-trondhjemite-granodiorite (TTG) associations due to show enrichment in TiO2, MgO and CaO, low contents of Sr, and Rb contents similar to samples with lower concentrations of silica, which are reflected in higher Rb/Sr ratios and lower Sr/Ba ratios. The REE patterns reveal low to moderate fractionation of HREE compared to LREE, and discrete or moderate negative Eu anomalies. It is stratigraphycally followed by TTG association correlated to Colorado Trondhjemite (~2.87 Ga) which displays gray color, medium-grained, and commonly a NW-SE to E-W foliation. In the southern of area, outcrops a body of 40 km 2, which comprises a small mountain of porphyritic leucogranodioritic rocks named Pantanal Leucogranodiorite . It is emplaced at TTG association and crosscutted, on its western portion, by deformed leucogranites. The Pantanal Leucogranodiorite shows peraluminous character and calc-alkaline affinity, with high contents of Ba and Sr. The REE patterns show nosignificant Eu anomalies and HREE are strongly fractionated, which is geochemically similar to Guarantã Suite (~2.87 Ga) from the Rio Maria Domain. Its origin may be related to low degrees of melting of TTG, probably accompanied by interaction with fluids enriched in K, Ba and Sr, derived from a metasomatized mantle. The leucogranites exhibit A-type geochemical signature and reduced character, and may have originated from the melt of dehydrated peraluminous calcic-alkaline rocks, during the Neoarchean. In the eastern portion of the Pantanal Leucogranodiorite was also identified ahornblende-biotite monzogranite which is geochemically similar to oxidized A-type granites, correlated to Neoarchean Vila Jussara Suite. Also, it correlated to Neoarchean subalkaline magmatism in the northern area, occur two granitic stocks. They comprise (i) tonalite to granodiorite with geochemical signature similar to oxidized A-type granites and show affinity with Vila Jussara Suite; and (ii) monzogranites which show reduced A-type granites signature and could be compared to Planalto Suite. At northern of the study area was identified an association of mafic-enderbitic rocks which comprises intensely deformed and recrystallized hornblende norite, pyroxene-hornblende gabbros, pyroxeneix hornblende monzonite, hornblende gabbros, amphibolites and enderbites, which are represented in the geological map as a WNW-ESE small elongated body , and a semicircular body controlled by shear zones. The textures observed in these rocks indicate that recrystallization occurs under relatively high temperatures, 6000C or above, and those rocks show metamorphic features. The geochemical behavior of these rocks suggests that the hornblende-norite, hornblende-gabbros and amphibolites are tholeiitic subalkalines, whereas enderbites, pyroxene-hornblende gabbro and pyroxene-hornblende monzonite exhibit calcalkaline signature. The low La/Yb ratios for mafic rocks indicate low degree of fractionation, whereas the high La/Yb ratios for enderbites reveal significant fractionation of HREE during formation and differentiation of its magmas, and the concavity of HREE pattern indicates probably influence of amphibole fractionation during its evolution. In the central and northcentral of area was recognized biotite-monzogranites with peraluminous and calc-alkaline signature and distinct REE patterns, which allowed us to distinguish two groups. The first shows higher REE enrichment, weak enrichment in LREE relative to HREE, and exhibit moderate negative Eu anomalies, indicating no significant fractionation of phases enriched in HREE and show possibly affinity with Bom Jesus Granite from Canaã dos Carajás area. The second group shows a sharp fractionation of HREE relative to LREE, with discrete or absent Eu anomalies, and concave HREE patterns indicating that amphibole was important phase during the fractionation of these rocks, like Serra Dourada and Cruzadão granites, also located in the Canaã dos Carajás area. This comparison should be enhanced as soon as further geochemical and geochronological data are available in order to a correlation can be evaluated.