The Guacuí and Batatal lineaments in the southern region of the state of Espírito Santo (southeastern Brazil) can be traced from satellite images for tens of kilometers. They are considered shear zones associated to the final tectonic stages of the Araçuaí-West Congo (A-WC) Orogen during the Ediacaran-Cambrian period. In order to understand their nature and tectonic implications for the development of the orogeny, we integrated geological and structural data based on fieldwork and detailed microstructural analysis. Data was collected along two profiles located at the central segments of both structures. The results demonstrated that the Guaçuí shear zone (GSZ) is a typical ductile transpressive shear zone with approximately 9 km width that shows numerous dextral kinematic indicators and records metamorphism of upper amphibolite facies. The GSZ shows different levels of intensity of dynamic deformation. The Batatal shear zone (BSZ) is a narrow brittle shear zone that shows essentially brittle microstructures (intercrystalline microfractures) revealing deformation at low-grade conditions (frictional regime). Based on their characteristics and the level of erosion of the rocks exposed in the region, we interpret that GSZ developed prior to BSZ.
Na região norte do Rio de Janeiro afloram rochas orto e paraderivadas neoproterozoicas de alto grau metamórfico, englobadas no Terreno Oriental da Faixa Ribeira. Dado a carência de estudos de detalhe na região, o presente trabalho contribui com novos aspectos de campo, petrografia, química mineral e geotermobarometria dos granitoides diatexíticos aflorantes na região entre São José de Ubá e São João do Paraíso, no noroeste fluminense. O litotipo é caracterizado por biotita-hornblenda gnaisses migmatíticos e protomiloníticos que são correlacionáveis a ortognaisses e granulitos do Complexo Serra da Bolívia (Domínio Cambuci da Faixa Ribeira). Dois litotipos neoformados são observados: um mesocrático, de caráter residual; e outro leucocrático, que correspondente ao leucossoma. O enriquecimento de K-feldspato no leucossoma em relação ao neossoma residual sugere baixos volumes de fusão por meio de reações de fusão envolvendo água. Aplicando-se diferentes geotermobarômetros, foram obtidas como condições de equilíbrio para o pico metamórfico 6,8 Kbar e 672–680°C (fácies anfibolito superior). Tais valores destoam dos encontrados na literatura para ouras rochas da região, reforçando a ideia de que os domínios do Terreno Oriental da Faixa Ribeira apresentam evoluções metamórficas distintas, em diferentes níveis crustais.
Optical physics applied to mineralogy becomes a complex concept, since it is based on concepts of refractoriness of isotropic and anisotropic materials, dependent on crystallographic parameters. The work aims to materialize these concepts in threedimensional schematic models in wood, such as optical indicatrix and figures of interferences, generated when the plane polarized or polarized light interacts with several transparent minerals. The pieces were applied in the classes of Mineralogy II of the Geology course of the Federal University of Espírito Santo in the years 2017 and 2018, presenting great receptivity by the dissenting body and ease in the profusion of the knowledge of the group of monitors and teachers. The geometric representations were also shown in workshops at the Natural History Museum of Southern Espírito Santo State with the objective of disseminating the geosciences. As a result, the classes obtained satisfactory results of approval and learning
Collisional granites of the Araçuaí Orogen, southeastern Brazil, record petrological and geochronological evidence for multiple crustal melting during the orogeny evolution. U-Pb zircon data indicate that these granites crystallized at 586 ± 2 M.y.High-grade metamorphism (M 1 ) involved partial melting by fl uid-absent reactions that produced the fi rst generation of garnet in temperatures of approx. 750°C. Preservation of the mineral assemblage A 1 (garnet-biotite-plagioclase-K-feldspar-quartz-ilmenite-melt) indicates that most of the generated melt was lost from these rocks at or near peak metamorphic conditions. A second metamorphic event (M 2 ) is characterized by growth of a second generation of garnet in preserved A 2 assemblage (garnet-sillimanite-biotiteplagioclase-K-feldspar-quartz-ilmenite-melt). Mineral equilibria modeling constrains conditions of M 2 metamorphism to 713-729 °C and 6.2-7.3 kbar. Retrograde assemblage (A 3 ) records equilibrium conditions at 610-660 °C. The Hf isotope composition indicates signifi cant crustal contribution to the genesis of the collisional granites. The elevated geotherms in thickened crust provide enough heat for the M 1 event at 562 ± 2 M.y.Subsequent heating probably associated to the transfer of mantle heat to the crust during the extensional thinning and gravitational collapse of the orogen lead to the M 2 event at 526 ± 4 M.y. This event is concomitant to the emplacement of the postcollisional magmas in the orogen.
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