During the Paleoproterozoic Era, the Brazilian cratons experienced orogenic events that modified the archean basement and sedimentary successions. In the southern São Francisco Craton, it can be recognized evidence of an orogenic event that happened between Rhyacian and Orosirian periods. It is related to the closure of an oceanic basin at this time, which led to the collision between the Archean Divinópolis and Campo Belo metamorphic complexes. Graphite schist occurs close to the cities of Formiga and Itapecerica (Minas Gerais), located between these complexes. To contribute to the understanding of the origin and metamorphism of the graphite from Formiga, petrographic studies, X-ray diffraction (XRD) and Raman spectroscopy analyses have been done. XRD and Raman methods revealed that the temperatures recorded by graphite are around 460°C. However, Raman data showed that the crystallite sizes correspond to higher metamorphic grade conditions (amphibolite to granulite facies). Temperatures of 460°C are probably associated with hydrothermal processes along faults in post-collisional stage. The presence of todorokite, a mineral typical of deep-sea Mn nodules formed by microorganisms, in association with graphite from Formiga, suggests a biogenic origin for the graphite occurrence.
As Geociências são uma área de conhecimento não muito aprofundada no ensino básico e, por isto, alguns equívocos ainda são feitos ao tentar explicar fenômenos relacionados a esta ciência. O projeto Geogle Maps foi criado com o intuito de incentivar o ensino e a popularização das Geociências utilizando um dispositivo acessível à maioria da população, o smartphone. Uma página no Instagram foi criada para mostrar exemplos de como os aplicativos Google Maps e Google Earth, compatíveis com quase todos os celulares, podem auxiliar no ensino de Geociências. As imagens de satélite permitem observar, por exemplo, limites de placas tectónicas. A visualização 3D permite caracterizar diferentes relevos. O Street View permite observar feições menores, como estruturas sedimentares, ígneas, rúpteis e dúcteis. São diversas as possibilidades e o projeto encoraja o leitor a buscar outras formas de utilizar os aplicativos no ensino de Geociências.
During the transition of Rhyacian to Orosirian periods a collision between the Archean Divinópolis and Campo Belo metamorphic complexes occurred in southern São Francisco Craton (SFC) followed by the collapse of the orogen. In the same region, the Statherian period is marked by a huge intraplate magmatic event that is represented in the area by the Para de Minas dyke swarm. Peraluminous granitoid occurrences are reported in the region of Formiga and Itapecerica (Minas Gerais – Brazil), surrounding high metamorphic grade khondalitic paragneisses and banded iron formations. To contribute to the understanding of the tectonic context of the southern SFC during the Paleoproterozoic era, these granitic rocks are studied based on petrographic, geochemical, and monazite U-Th-Pb geochronological analyzes. They were characterized as S-type (metasedimentary origin) peraluminous metamonzogranites, with crustal geochemical signature, and genesis related to anatexis in syn- to post-collisional environment. The geochronological results yielded two groups of Orosirian (~1,90 Ga) and Statherian (~1,78 Ga) ages. These results are related, respectively, to the collapse of the Rhyacian-Orosirian orogen and to the regional warming, associated with the Avanavero-Xiong’er LIP that is represented in the area by the Pará de Minas dyke swarm.
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