Navegando por Autor "NOGUEIRA, Bruna Karine Correa"

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Petrografia, geoquímica e geocronologia da Suíte Rosário, Fragmento Cratônico São Luís, MA
(Universidade Federal do Pará, 2015-10-20) NOGUEIRA, Bruna Karine Correa; GORAYEB, Paulo Sérgio de Sousa; http://lattes.cnpq.br/4309934026092502
The region between the Gurupi and Itapicuru rivers comprises a relatively large area in the northeastern of Pará and northwestern of Maranhão states that exposes Paleoproterozoic granitic suites and metavolcanosedimentar sequences from São Luís Cratonic Fragment, which is bordered by Neoproterozoic gneisses, metasedimentary and granitoid rocks from Gurupi Belt. Further east of this geoctectonic unit, approximately 70 km south of São Luís city, another portion of this cratonic fragment outcrops, represented by the Rosário Intrusive Suite (RIS), target of this work, which involved petrographic, lithochemical and geochronological studies in order to understand the crustal evolution of the granitoid rocks of this suite. The RIS comprises a set of multiple tonalitic, granodioritic and granitic plutons that shows partially textural, structural and mineralogical transformations related to strain along to trancurrent shear zones. The studied granitoid rocks are exposed in erosional windows, which are found in both gravel quarries o valleys and river banks. Three main rock types of this suite have been mapped in this work: meta-quartz diorites, meta-tonalites with variable melatonalites and metagranodiorites. They usually exhibit preserved igneous textures, as hypidiomorphic granular texture, with weak deformational effects and overlapped mylonitic features. The mineral assemblage is mainly composed of plagioclase, quartz, microcline, hornblende, titanite, and minor biotite, zircon, apatite, and opaque minerals. Secondary mineralogical phases are evidenced by the transformation of plagioclase into sericite, epidote and carbonate, biotite and hornblende into chlorite, and tremolite-actinolite as alteration product of hornblende. The rocks are classified as metaplutonic due to show metamorphic transformations by influence of deformation and new formation of minerals in shear zones with metamorphism reaching greenschist facies conditions (shear metamorphism). These ganitoids generally have geochemical characteristics with SiO2 content between 49% and 78%, K2O between 0.16 and 3%, MgO of 0.13-8%, CaO content of 1-8%, TiO2 varying from 0.3% to 0.7%, and Na2O content from 1% to 6%. The values of K2O/Na2O ratio are generally bellow 1, with few values up or next to 1. According to Shand alumina saturation index, these rocks are metaluminous. In geochemical classification diagrams, the rocks plot mainly in the fields of diorite, tonalite, granodiorite and granite, coincident with petrographic data, allowing fit them into calc-alkaline series. Trace elements present negative anomalies of Rb and Nb, with distribution pattern of LREE enrichment in relation to HREE [(La/Yb)N = 3-25], indicating an accentuated REE fractionation, besides of incipient negative and positive Eu anomalies (Eu/Eu* = 0.82 a 1.1). The geochemical analyses point out to an I-type calc alkaline affinity related to a magmatic arc environment. Zircon U-Pb radiometric data furnished ages of 2170.6±4 Ma, 2173.8±7.7 Ma, 2178.6±7.4 Ma, 2145±13 Ma e 2158.2±7.8 Ma, which represent the Paleoproterozoic (Rhyacian) placement ages of the Rosário Suite. Sm-Nd isotopic data furnished TDM model ages between 2.24 and 2.37 Ga with εNd from +1.0 and +2.5 (t = 2.17 Ga). In the εNd versus time diagram, all samples are positioned within the field of Paleoproterozoic crust of São Luís Fragment Cratonic, indicating dominantly Rhyacian crustal sources for parental magmas. In comparison, these rocks show geochemical and geochronological characteristics similar to others plutonic suites from São Luís Cratonic Fragment, as the Tromaí Intrusive Suite (TIS). Although the RIS shows petrographic differences, the TIS granitoids are also positioned in the fields of metaluminous, I-type calc alkaline affinities and subduction-related setting. The data from this study with geological and geochronological available data from literature imply to a magmatism that extended up to 1,000 Km, forming large Paleoproterozoic tonaliticgranodioritic batholites, thus indicating an important event of continental crust formation in this area through intense plutonism related to the Transamazonian/Eburnean event. In Western Africa Craton, a similar geological setting is interpreted as the result of the collision and amalgamation of several magmatic arcs and Archean terrains during Eburnean (Transamazonian) event, suggesting a link between the São Luís Cratonic Fragment and Western African in the West Gondwana, and then, being part of the same pre-derived unit. The geological events happened in this Brazilian region may be compared to those that led to the formation of Birrimian terrains in Western Africa.
Acesso aberto (Open Access)
Rhyacian evolution of the eastern são luís craton: petrography, geochemistry and geochronology of the rosário suite
(Sociedade Brasileira de Geologia, 2017-06) NOGUEIRA, Bruna Karine Correa; GORAYEB, Paulo Sérgio de Sousa; DANTAS, Elton Luiz; LEAL, Rafael Estumano; GALARZA TORO, Marco Antônio
The São Luís Cráton comprises an area between northeast Pará state and northwest Maranhão that exposes Paleoproterozoic granitic suites and meta-volcanosedimentary sequences. In the east of this geotectonic unit, about 70 km south of São Luís, there is a portion of the São Luís Craton, represented by the intrusive Rosario Suite (RS). This work is focused on rocks of this suite, including petrographic, lithochemical and geochronological studies to understand the crustal evolution of these granitoid rocks. The rock spectrum varies from tonalitic to granodioritic, quartz dioritic and granitic compositions, and there are partial structural and mineralogical changes related to deformation along transcurrent shear zones. The geochemical studies show granitic metaluminous compositions of the calc-alkaline series with I-type affinity typical of magmatic arc. Rare earth elements show marked fractionation and slight Eu positive or negative anomalies (Eu/Eu* = 0.82 to 1.1). Zircon U-Pb data provided consistent ages of 2165 ± 7 Ma, 2170 ± 7 Ma, 2170 ± 7 Ma, 2161 ± 4 Ma and 2175 ± 8 Ma, dating emplacement of these granitoids as Paleoproterozoic (Rhyacian). Sm-Nd isotopic data provided model ages (TDM) of 2.21 to 2.31 Ga with positive values of εNd +1.9 to +3.2 (t = 2.17 Ga), indicating predominantly Rhyacian crustal sources for the parental magmas, similar to those ones found in other areas of the São Luís Craton. The data, integrated with published geological and geochronological information, indicate the occurrence of an important continental crust formation event in this area. The Paleoproterozoic evolution between 2.17 and 2.15 Ga is related to the Transamazonian orogeny. The granitoids of the Rosario Suite represent the main phase of continental arc magmatism that has continuity in other parts of the São Luís Craton and can be correlated with Rhyacian accretionary magmatism in the northwestern portion of the Amazonian Craton that amalgamated Archean terrains during the Transamazonian orogeny