Navegando por Orientadores "BARROS, Carlos Eduardo de Mesquita"

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Evolução petrológica e estrutural das rochas metabásicas e granitóides da Serra Leste, Província Mineral de Carajás
(Universidade Federal do Pará, 2008-09-25) NASCIMENTO, Valéria Marinho do; MOURA, Augusto Veloso; http://lattes.cnpq.br/1035254156384979; BARROS, Carlos Eduardo de Mesquita; http://lattes.cnpq.br/3850881348649179
In the Serra Leste, located to the northeast of Curionópolis village, next to the Serra Pelada, one has identified mafic/ultramafic rocks belonging to the Luanga Complex, metavulcano-sedimentary rocks, metagabbros and deformed granitoids. Quartzites, banded iron formations and micaschists are associated with metabasalts. Post-Archaean diabase and gabbro dykes occur subordinately. The metabasalts display subophitic texture, partially modified subophitic texture and nematoblastic/granoblastic texture. These rocks underwent three phases of metamorphism. The former one (M0) is represented by hydrothermal alteration developed in seawater environment under greenschist conditions. The second phase (M1) has thermal nature and developed in response to the emplacement of 2.85 Ga granitoids. Deformation related to the granite emplacement and thermal metamorphism produced a localized foliation (N40ºE). The third metamorphic phase (M2) is marked by the thermal effects of hornblende hornfels facies, promoted by the 2.76 Ga granites. Locally one can describe a foliation (S2) that was developed synchronously to the M2 phase. Metabasites from the Serra Leste area have subalkaline signature comparable to that of the iron-rich tholeites. The chemical characteristics of these metabasalts are similar to those of the greenstones from the Munro Township (Canada). Trace elements behavior permits tentatively to compare these rocks to the basalts from island arc or oceanic crust. Biotite-quartz diorites, biotite trondhjemites, hornblende-biotite trondhjemites, biotite granodiorites and biotite monzogranites are identified in the Serra Leste area. These rocks have medium-K calc-alkaline signature, comparable to the I-type and CA-2 rocks from volcanic arcs. The adopted petrogenetic model to explain the origin of these magmas is the partial melting of metabasalts in a subduction zone context. Modification of magmas composition could be explained by some degrees of fractioning crystallization of feldspar, amphibole and minor pyroxene. These granitoids show layering and preferred orientation of minerals, both developed during the magma emplacement and crystallization. The presence of metabasite xenoliths in the 2.85 Ga granitoids as well as the thermal effects promoted by the granitoids on the metabasites lead to conclude that the supracrustal rocks are older than 2.85 Ga.
Acesso aberto (Open Access)
Geologia estrutural, geoquímica, petrografia e geocronologia de granitóides da Região do Igarapé Gelado, norte da Província Mineral de Carajás
(Universidade Federal do Pará, 2004) BARBOSA, Jaime dos Passos de Oliveira; BARROS, Carlos Eduardo de Mesquita; http://lattes.cnpq.br/3850881348649179
To the north of the Carajás range granitoid rocks occur in an elliptical domain oriented in toWNE-ESE direction. These rocks are limited to the south and to the north by metabasalts and banded iron formations belonging to the Itacaiúnas Supergroup. The granitoids show a penetrative foliation in the body scale, striking in the WNW-ESE and E-W directions, concordant with the regional structures. Steep dipping foliations predominate but flat lying ones are locally present. Foliations are continuous, smooth, and marked by the weak to strong preferred orientation of mafic minerals and feldspars and by the flattened quartz aggregates. Stronger degrees of deformation were reached on decimeter-wide E-W mylonite zones. Discrete centimeter-wide conjugate shear bands are locally described. The structural evolution of the studied granitoids indicates emplacement synchronously to N-S compressive stress, similarly to other 2.7 Ga granitoids present in the region. Granodiorites and monzogranites predominate largely over tonalites, leucomonzogranites and syenogranites. Quartz-feldspathic pegmatites occur locally filling decimeter-wide veins. In less deformed rocks, oriented granular textures are common. Sometimes, these rocks show graphic texture accompanied of corroded amphibole crystals (honeycomb or sieve textures). Both textural evidences suggest fast crystallization controlled by undercooling conditions and emplacement at shallow levels. In moderate to strongly deformed rocks corrosion of amphibole and biotite produce symplectite textures along the surfaces parallel to foliation. In this case the corrosion is stress-controlled and it suggests deformation history of unconsolidated rocks. Two groups of granitoids can be discriminated on the basis of whole-rock chemical data: alkaline (ALK-3) and calc-alkaline (CA-2) granitoids. The rocks of both groups have moderate to high Y, Nb and Zr contents so that the calc-alkaline granitoids in some diagrams plot on the Atype field. The alkaline and the calk-alkaline rocks from the Igarapé Gelado region were most probably originated by partial melting of continental crust. The high Zr contents seem to indicate that both group of rocks were generated by high-temperature partial melting of crustal rocks. Differences of rare-earth elements patterns of the studied ALK-3 and CA-2 granitoids could reflect different depths of the source rocks. The calc-alkaline magmas, are depleted in heavy rareearth elements, compared to alkaline ones and would be produced at deeper levels. Pb-Pb (evaporation) zircon dating yielded 2.5 Ga on the low temperatures steps and 2.73 Ga on the steps of higher temperatures. The later value is considered as the minimum age to the granitoids crystallization and it is close to the ages obtained by other authors on quartz-fedspathic veins that crosscut rocks from the Igarapé-Pojuca Group. The age of 2.5 Ga could reflect some degree of perturbation on the U-Pb system. The studied granitoids belong to the syntectonic magmatism (e.g. Estrela, Planalto, Serra do Rabo, Plaquê granites) that took place in the Carajás region 2.7 Ga ago.
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Geologia, geoquímica e geocronologia do granito Serra do Rabo, província mineral de Carajás
(Universidade Federal do Pará, 2002-03-25) SARDINHA, Alex Souza; BARROS, Carlos Eduardo de Mesquita; http://lattes.cnpq.br/3850881348649179
Acesso aberto (Open Access)
Petrologia, geologia estrutural e aerogeofísica da porção Leste do Domínio Bacajá, Província Maroni-Itacaiúnas
(Universidade Federal do Pará, 2008-09-30) SOUSA, Cristiane Silva de; BARROS, Carlos Eduardo de Mesquita; http://lattes.cnpq.br/3850881348649179
The Bacajá Domain is located in the centrar-eastern part of the Pará State, in the southern part of the Maroni-Itacaiúnas Province, which is characterized by a large exposure of Paleoproterozoic and Archean rocks reworked during the Transamazonian Cicle Orogeny. The study area is situated in the Novo Repartimento town, to the south of the Maracajá village, where monzogranites, granodiorites and tonalites, as well as quartzites, granulites and gneisses are exposed. Amphibolites occur as xenoliths in the granitoids. Diabasie dikes are found locally. Aerogeophysical data obtained has improved the cartography of the mapped area. The magnetic structures, mainly determined from the horizontal (x, y) and vertical derivatives (z), evidence a major set of lineaments trending WNW-ENE, consistent with the regional structures. NE-SW lineaments comprise mafic dikes. Maps of potassium, uranium and thorium channels, total count and ternary (RGB, CMY) has allowed the individualization of ten gamma-spectrometric domains. High radiometric values correspond to biotite-granites and gneisses. Leucomonzogranites, hornblenda granites and quartzites show moderate to low radiometric values. A penetrative foliation is recognized at regional scale in the granitoids and displays NW-SE and WNW-ESE strikes, generally with subvertical dips. Primary layering showing gentle to steep dip evolves to a secondary foliation and to mylonitic zones, both concordant. The mineral lineation is weak and have gentle plunges. Microstructural features indicate a transition from magmatic flow to solid-state deformation during the development of foliations in granitoids. Structural analysis of the granitoids suggests that the regional deformation and the emplacement of great volume of intermediate to felsic magma were contemporaneous. Pervasive foliation at the regional scale and homogeneous foliation at the outcrop scale are very common features in syntectonic plutonic belts, and generally generated in a magmatic arc setting. Fourteen petrolographic facies are recognized in the granitoids, so they can represent several plutons. These rocks are metaluminous, medium-to high K calcalkaline and distinguished by high light REE and low heavy REE contents. Eu negative anomalies are very weak or absent. Petrological, geochemical and structural features of the granitoids suggest a magmatic arc environment for the studied region, and that granitoid emplacement is contemporaneous with a compressive tectonic event.