Navegando por Autor "LEAL, Rafael Estumano"

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Geoquímica e geocronologia U-Pb, Sm-Nd e Rb-Sr dos granitoides orosirianos do domínio Erepecuru-Trombetas, Província Amazônia Central, Noroeste do Pará
(Universidade Federal do Pará, 2015-08-10) LEAL, Rafael Estumano; COSTA, Lúcia Travassos da Rosa; http://lattes.cnpq.br/3352314623448523; https://orcid.org/0000-0002-2666-9824; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645
The granitic rocks of the northwestern Pará State are part of two large volcano- plutonic associations that marked the central region of the Amazonian Craton during Orosirian. The area of this study is located in the southwest portion of the Erepecuru- Trombetas Domain, south of the Guyana Shield. The oldest association recently mapped and dated at about 2.0-1.95 Ga, is formed by volcanic rock of Igarapé Paboca formation and granitoids of Caxipacoré Suite. The youngest association (1.90-1.86 Ga) is related to the Água Branca and Mapuera suites and the effusive and pyroclastic rocks of Iricoumé Group. Petrographic studies in the Caxipacoré, Água Branca and Mapuera granitoids allowed the definition of five granitoids varieties (quartz-monzonite, monzonite, monzogranites, syenogranites and ácali-feldspar granites) with variable content of hornblende and biotite, the main mafic phases. In general, they are isotropic rocks, leucocratic, inequigranular, medium- to coarse-grained with hypidiomorphic granular, rapakivi, granophyric and micro-porphyritic textures. The geochemical characterization allowed the distinction of two rock groups with different signatures. The first group formed by Caxipacoré and Água Branca suites, shows high-K to shoshonitic, magnesian, metaluminous to peraluminous calc-alkaline trends. LILE- enrichment (e.g. K, Rb, Ba and Sr), strong negative Nb anomalies, moderate heavy REE- fractionation and weak Eu anomalies are common characteristics of these granites. The second lithological group formed by Mapuera Suite, comprises acid rocks (71.29
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