2019-02-252019-02-252015-10-20NOGUEIRA, Bruna Karine Correa. Petrografia, geoquímica e geocronologia da Suíte Rosário, Fragmento Cratônico São Luís, MA. Orientador: Paulo Sergio de Sousa Gorayeb. 2015. 91 f. Dissertação (Mestrado em Geologia e Geoquímica) – Instituto de Geociências, Universidade Federal do Pará, 2015. Disponível em: http://repositorio.ufpa.br/jspui/handle/2011/10696. Acesso em :.https://repositorio.ufpa.br/handle/2011/10696The 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 AbertoPetrologia - MaranhãoGeocronologiaGeologia isotópica - MaranhãoFragmento Cratônico São LuísPetrografia, geoquímica e geocronologia da Suíte Rosário, Fragmento Cratônico São Luís, MADissertaçãoCNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIAPETROLOGIA E EVOLUÇÃO CRUSTALGEOQUÍMICA E PETROLOGIA