Facies analysis and depositional environments of the Vazante Group in the region of Morro Agudo mine, Paracatu, northwest of Minas Gerais state, Brazil

Rochas do Grupo Vazante afloram no noroeste do estado de Minas Gerais, em uma faixa contínua de aproximadamente 250 km, da região de Vazante, ao sul, até Unaí, ao norte. Nessa região está localizada a mina de zinco e chumbo de Morro Agudo, que juntamente com os depósitos de Vazante, Ambrósia e Fagundes, todos hospedados no Grupo Vazante, compõe a principal província zincífera do país. Foram descritas, em seis testemunhos de sondagem e afloramentos de campo na região, 12 fácies sedimentares e quatro associações de fácies (AFs), que indicam deposição em ambiente de margem passiva mista carbonática-siliciclástica. A associação mais basal (AF01) é composta por pelitos e ritmitos silto-arenosos carbonosos, representando sedimentação em plataforma profunda de baixa declividade, em regime de transgressão marinha. Após a inundação máxima, em trato de mar alto, depositou-se a AF02 em ambiente de recife com barreiras em borda de plataforma, composta por dolomitos laminados com estromatólitos, dolarenitos e brechas dolareníticas, e ainda pelitos carbonáticos carbonosos com fácies diamictito. O abaixamento do nível relativo do mar gerou uma regressão forçada e a deposição da AF03 em trato de sistema do estágio de queda. É composta, na base, por diamictito argilo-carbonoso com fragmentos de AF02, passando a pelito e ritmito silto-arenoso. A retomada da subida do nível relativo do mar proporcionou a deposição da AF04 e ainda de rochas da AF03 em posição mais distal. A AF04 é composta por dololutitos argilosos laminados e maciços, e dolarenitos intraclásticos depositados em plataforma carbonática. O padrão de empilhamento observado sugere que a deposição de todas as unidades ocorreu progressivamente, em processo de subida do nível relativo do mar Vazante Group rocks outcrop in the northwest of Minas Gerais state, in a continuous belt of approximately 250 km, from the region of Vazante city, in the south, to Unaí city, in the north. In this region is the zinc and lead mine of Morro Agudo, which together with the deposits of Vazante, Ambrósia and Fagundes, all housed in the Vazante Group, make up the main zinc province of the country. Twelve sedimentary facies and four facies associations (AFs) were described in six drill holes and outcrops, that indicate deposition in a carbonate-siliciclastic mixed passive margin setting. The most basal association is AF01, composed by carbonaceous mudstone and silt-sand rhythmic, representing sedimentation in a deep platform of low slope angle, in a regime of marine transgression. After the maximum flood surface, in the highstand systems tract, AF02 was deposited in a reef setting with a barrier at the platform edge. It is composed of laminated dolomites with stromatolites, dolarenites and dolarenite breccia, and carbonate carbonaceous mudstones with interleaved diamictite facies. The fall in relative sea level led to a forced regression and the deposition of AF03 in a forced regressive system’s tract. It is composed, at the base, by carbonaceous diamictite with AF02 fragments, passing to mudstone and silt-sand rhythmithes. The return of the rise of the relative sea level provided the deposition of AF04 and AF03 rocks in a more distal position. AF04 is composed by laminated and massive argillaceous dololutite, and intraclastic dolarenite, deposited in carbonate marine platform. The observed stacking pattern suggests that the deposition of all units occurred progressively, in process of rising relative sea level&nbsp

Filling Materials in Brittle Structures as Indicator of Cenozoic Tectonic Events in Southeastern Brazil

The filling materials in brittle structures can provide useful information about the Cenozoic evolution developed over proterozoic terrains. When these materials are affected by faults, they record deformation phases that can be determined chronologically and, in the occurrence of lateritic materials, it is possible to infer the paleoenvironmental conditions during the mineral formation. This work aimed to identify crystalline phases of brittle structure filling materials and to propose evolutionary interpretations for Cenozoic tectonic reactivation based on literature data. The study area is located in the Southern part of the Espírito Santo State, near the Brazilian Southeastern Continental Margin, where proterozoic geological structures have been reactivated since the mesozoic rift phase, up to the Holocene. The mineral assemblage found in the filling materials includes primary minerals such as quartz, muscovite, microcline, rutile, titanite, and bannisterite; and the weathering minerals such as kaolinite, illite, hematite, goethite, hydrobiotite, lithiophorite and, birnessite. The mineralogical association found in the filling materials denotes the action of fluid phases with mineral precipitation at the brittle discontinuities during the weathering processes that occurred during the Cenozoic, probably between the Miocene and the Pleistocene. The faults, which striations are marked on the filling materials, originated after (in the case of the manganese oxides) or during (in the case of the illite) the mineral formation, indicating that the maximum age of these faults is in the Miocene. The origin of the brittle structures that affected the filling materials studied here is linked to the uplifting of the Continental Brazilian Margin, when ancient geological structures were reactivated as normal faults due to the local action of an extensional regime.The filling materials in brittle structures can provide useful information about the Cenozoic evolution developed over proterozoic terrains. When these materials are affected by faults, they record deformation phases that can be determined chronologically and, in the occurrence of lateritic materials, it is possible to infer the paleoenvironmental conditions during the mineral formation. This work aimed to identify crystalline phases of brittle structure filling materials and to propose evolutionary interpretations for Cenozoic tectonic reactivation based on literature data. The study area is located in the Southern part of the Espírito Santo State, near the Brazilian Southeastern Continental Margin, where proterozoic geological structures have been reactivated since the mesozoic rift phase, up to the Holocene. The mineral assemblage found in the filling materials includes primary minerals such as quartz, muscovite, microcline, rutile, titanite, and bannisterite; and the weathering minerals such as kaolinite, illite, hematite, goethite, hydrobiotite, lithiophorite and, birnessite. The mineralogical association found in the filling materials denotes the action of fluid phases with mineral precipitation at the brittle discontinuities during the weathering processes that occurred during the Cenozoic, probably between the Miocene and the Pleistocene. The faults, which striations are marked on the filling materials, originated after (in the case of the manganese oxides) or during (in the case of the illite) the mineral formation, indicating that the maximum age of these faults is in the Miocene. The origin of the brittle structures that affected the filling materials studied here is linked to the uplifting of the Continental Brazilian Margin, when ancient geological structures were reactivated asnormal faults due to the local action of an extensional regime

Age, provenance and tectonic setting of the high-grade Jequitinhonha Complex, Araçuaí Orogen, eastern Brazil

O Complexo Jequitinhonha é uma unidade sedimentar extensa da porção nordeste do orógeno Araçuaí, metamorfizada na transição entre as fácies anfibolito-granulito há cerca de 580-540 Ma. A unidade é composta por paragnaisses kinzigíticos com intercalações de grafita-gnaisse, quartzito e rochas calcissilicáticas. Dados U-Pb de zircão detrítico de uma amostra de quartzito e novos dados geoquímicos (nove amostras) e isotópicos (Sm-Nd) (dez amostras) são aqui apresentados. De maneira concomitante a dados previamente publicados, esses dados mostram que: (1) a geoquímica dos paragnaisses sugere uma afiliação do tipo margem passiva para as rochas metassedimentares; (2) zircões detríticos apresentam populações de idade U-Pb entre 0,9 e 2,5 Ga; e (3) dados isotópicos de Nd apresentam idades modelo T DM entre 1,6 e 1,8 Ga e εNd (575 Ma) ao redor de -7,5. Esses dados revelam uma mistura de fontes, envolvendo magmatismo de rift Criogeniano a Mesoproterozoico e o embasamento Paleoproterozoico-Arqueano do paleocontinente São Francisco-Congo, e sugerem uma forte correlação entre o Complexo Jequitinhonha e o Grupo Macaúbas, compondo a mais importante bacia precursora do orógeno Araçuaí. Além da natureza exclusivamente sedimentar do complexo, fatias ofiolíticas não foram encontradas na área, reforçando a interpretação da terminação ensiálica de um golfo e que o paleocontinente São Francisco-Congo não foi separado ao norte da região, agindo como uma única peça durante o Neoproterozoico.The Jequitinhonha Complex of the northeastern Araçuaí orogen is an extensive sedimentary unit metamorphosed in the amphibolite-granulite facies transition around 580-545 Ma. The unit consists of Al-rich (kinzigitic) paragneisses with decametric intercalations of graphite gneisses and quartzites, and centimetric to metric lenses of calcsilicate rocks. A new detrital zircon U-Pb age spectrum is reported for a sample of quartzite, and whole-rock geochemical (major and trace elements, 9 samples) and Sm-Nd isotope data (10 samples) for Jequitinhonha Complex paragneiss. Together with published data these show that: (1) the geochemistry of paragneiss samples of the Jequitinhonha Complex are similar to those of passive margin sedimentary protoliths; (2) detrital zircon data yield U-Pb age populations between ca. 0.9 and 2.5 Ga; and (3) Sm-Nd TDM model ages range from 1.6 to 1.8 Ga and εNd(575 Ma) around -7.5. The data reveal a mixture of Cryogenian to Mesoproterozoic rift-related igneous rocks with the Palaeoproterozoic-Archaean basement rocks of the São Francisco-Congo palaeocontinent as the main source areas, and also support the correlation between the Jequitinhonha Complex and the passive margin units of the upper Macaúbas Group, constituting the precursor basin of the orogen. Our results, with the absence of ophiolites in the Jequitinhonha Complex, reinforce the interpretation that the São Francisco-Congo palaeocontinent was not divided to the north of the focused region, suggesting an ensialic termination of a gulf during the Neoproterozoic

Stratigraphy, petrography and tectonics of the manganese-bearing Buritirama Formation, Northern Carajás Domain, Amazon Craton

Abstract The Buritirama Formation (BF) occurs at the extreme north of the Carajás Province, close to the contact with the Bacajá domain, in the southeastern portion of the Amazon Craton (Brazil). The BF consists of a 40 km long, ca. 3 km wide NW-SE trending structure arranged in four imbricated thrusts that individualize three main stratigraphic units. The lower unit is composed of orthoquartzite followed by carbonate-silicate rocks. The intermediate unit hosts a supergene manganese ore deposit formed by weathering of kutnohorite-rich marble. Quartzite/mica-quartz schist followed by carbonate-silicate rocks make up the upper unit. The local basement is constituted by orthogneiss-migmatite (Xingu Complex) and the Buritirama metagranite. Mineral chemistry data and metamorphic textures record high consumption of carbonate and quartz to produce clinopyroxenes. The structural assemblage of the BF records mass transport from NE to SW and the following deformational phases: D1 (compressional ductile), D2 (compressional brittle) and D3 (extensional brittle). The BF is interpreted as part of a platformal depositional system positioned at the border of the Carajás domain, which was probably inverted, deformed and metamorphosed during the Transamazonian event (ca. 2.1 Ga), in a deformation belt related to the amalgamation between the Carajás and Bacajá domains

Stratigraphy, tectonics and detrital zircon U-Pb (LA-ICP-MS) geochronology of the Rio Preto Belt and northern Paramirim corridor, NE, Brazil

ABSTRACT: Two important Proterozoic metasedimentary sequences, the Rio Preto and Santo Onofre Groups, crop out along the northwestern margin of the São Francisco craton and in northern Paramirim corridor, respectively. The Rio Preto Group, involved in the eponymous fold-thrust belt along the northwestern cratonic boundary, comprises the Formosa (garnet schist, quartz-mica schist, quartzite, chlorite-sericite schist and ferriferous quartz schist) and Canabravinha (quartzite, micaceous quartzite, metarhytmite, phylite, schist and metaturbidite) formations. The Santo Onofre Group occurs exclusively in the Paramirim corridor, and is composed of quartzite and minor carbonaceous or Mn-rich phylite. These units record sedimentation in shallow to deep-water marine settings related to rift basins, and were deformed and metamorphosed under greenschist facies conditions during the Brasiliano orogeny. Here we present 427 new detrital zircon U-Pb ages, which constrain the maximum depositional ages of ca. 971 Ma for the Santo Onofre Group, ca. 912 Ma for the Canabravinha Formation, and ca. 965 Ma for the Formosa Formation of the Rio Preto Group. Our data suggests that the Santo Onofre and the Rio Preto Groups accumulated in two distinct basin settings. The latter, composed mostly of sandy rocks, would represent a relatively stable, shallow-marine shelf environment. The Rio Preto Group, with metadiamictite, quartzite, pelitic and rhythmitic rocks, represents a shallow to deep marine environment influenced by gravity flows. Both groups were probably deposited in the Late Tonian, and are potential correlatives of the lower (pre-glacial) units of the Macaúbas Group of the Araçuaí belt

Hidrogeoquímica do Sistema Aquífero Cristalino no sul do estado do Espírito Santo – Brasil

A demanda por água subterrânea no estado do Espírito Santo vem crescendo consideravelmente frente aos eventos de escassez que marcaram os últimos anos. No entanto, a carência de conhecimentos hidrogeológicos compromete a locação de poços e a previsão da qualidade das águas, especialmente nos terrenos de rochas cristalinas. Este trabalho teve como objetivo uma avaliação hidrogeoquímica e da qualidade da água subterrânea do Sistema Aquífero Cristalino na Bacia Hidrográfica do Rio Itapemirim (BHRI), situada no sul do estado do Espírito Santo, descrevendo as variações composicionais e os condicionantes que influenciam a qualidade da água subterrânea. A compartimentação litológica e geomorfológica da bacia e as condições climáticas são os fatores que influenciam na hidrogeoquímica em escala regional, enquanto o uso e a ocupação do solo exercem influência pontual. Na porção da Alta BHRI, com relevo acidentado e predomínio de atividades agropecuárias, ocorrem principalmente águas bicarbonatadas cálcicas e bicarbonatadas cálcicas-magnesianas, pouco mineralizadas comparativamente à porção central da bacia, com composição química governada essencialmente pelo intemperismo das rochas silicáticas. Embora sejam águas de boa qualidade, alterações locais podem ocorrer em razão do nitrato proveniente de atividades antrópicas. Na porção da Média BHRI, com menores altitudes e relevo mais suave, as águas são predominantemente bicarbonatadas sódicas e cloretadas sódicas, com maior mineralização em relação à porção alta da bacia em razão da contribuição de rochas silicáticas em associação com litotipos carbonáticos, como mármores e calciossilicáticas. Nessa porção da bacia, as condições climáticas, com temperaturas mais altas e menor umidade do ar na área central da bacia, topograficamente mais rebaixada, também podem contribuir com o enriquecimento mineral em decorrência da evaporação da água que infiltraThe groundwater demand in the state of Espírito Santo (Brazil) has been growing considerably due to the events of drought in recent years. However, the lack of hydrogeological knowledge compromises water-well location and the prediction of the quality of water, mainly where crystalline rocks occur. This work aimed to evaluate the hydrogeochemical and groundwater quality of the Crystalline Aquifer System in the Itapemirim River Watershed (BHRI), located in the Southern part of Espírito Santo, describing the compositional variations and the conditioners that control groundwater quality. The lithological and geomorphological compartmentalization of the watershed in addition to climatic conditions are the factors that influence the groundwater geochemistryat a regional scale, while the land use and occupation exert a local influence. In the Upper BHRI portion, with steep relief and predominance of farming, there are mainly low-mineralized calcic bicarbonated and calcic-magnesian bicarbonated waters with components provided by the weathering of metamorphic and igneous silicate rocks. Although these are good quality waters, local changes can occur due to the presence of nitrate from human activities. In the Medium BHRI portion, with softer relief and lower topographic altitudes, groundwater is mainly of sodium chlorinated and sodium bicarbonated types, more mineralized due to the contribution of silicate rocks in association with carbonated lithotypes, such as marbles and calcium-silicate rocks. The climatic conditions, with higher temperatures and lower air humidity in the central area of the basin, which is topographically lower, can also contribute to mineral enrichment due to the evaporation of water in the soil

Age, provenance and tectonic setting of the high-grade Jequitinhonha Complex, Araçuaí Orogen, eastern Brazil

ABSTRACT: The Jequitinhonha Complex of the northeastern Araçuaí orogen is an extensive sedimentary unit metamorphosed in the amphibolite-granulite facies transition around 580-545 Ma. The unit consists of Al-rich (kinzigitic) paragneisses with decametric intercalations of graphite gneisses and quartzites, and centimetric to metric lenses of calcsilicate rocks. A new detrital zircon U-Pb age spectrum is reported for a sample of quartzite, and whole-rock geochemical (major and trace elements, 9 samples) and Sm-Nd isotope data (10 samples) for Jequitinhonha Complex paragneiss. Together with published data these show that: (1) the geochemistry of paragneiss samples of the Jequitinhonha Complex are similar to those of passive margin sedimentary protoliths; (2) detrital zircon data yield U-Pb age populations between ca. 0.9 and 2.5 Ga; and (3) Sm-Nd TDM model ages range from 1.6 to 1.8 Ga and εNd(575 Ma) around -7.5. The data reveal a mixture of Cryogenian to Mesoproterozoic rift-related igneous rocks with the Palaeoproterozoic-Archaean basement rocks of the São Francisco-Congo palaeocontinent as the main source areas, and also support the correlation between the Jequitinhonha Complex and the passive margin units of the upper Macaúbas Group, constituting the precursor basin of the orogen. Our results, with the absence of ophiolites in the Jequitinhonha Complex, reinforce the interpretation that the São Francisco-Congo palaeocontinent was not divided to the north of the focused region, suggesting an ensialic termination of a gulf during the Neoproterozoic

Geochemistry and sedimentary provenance of the Upper Cretaceous Uberaba Formation (Southeastern Triângulo Mineiro, MG, Brazil)

ABSTRACT: The campanian Uberaba Formation, which crops out around the homonymous town, is composed of greenish lithic sandstones and conglomerates with possible volcanoclastic contribution. In this unit, heavy minerals such as ilmenite, garnet, perovskite and magnetite, besides clinopyroxene, plagioclase, quartz, calcite and apatite, are found. The Uberaba Formation geochemistry is marked by high grades of Ba, Ta, La, Nb and Th, with flat (no Eu anomaly) and highly fractionated (LaN/YbN = ca. 128) chondrite-normalized rare earth elements. Mineral chemistry analyses of detrital garnets from the Uberaba Formation indicate the predominance of chorlomite with an affinity to crustal garnets (G3). The sedimentary provenance of the Uberaba Formation corresponds to a mixing of materials from the alkaline districts of the Alto Paranaíba and from the erosion of the Serra Geral Formation and the Canastra and Araxá groups. Diamond-producing conglomerates which crop out nearby, in Romaria, were considered by some authors as correlated to the Uberaba Formation. However, the composition of garnets recovered from those conglomerates is different, plotting in the field of mantle garnets (G9/G10). We consider, then, that those units are not correlated, and that the Uberaba Formation is not a possible source for the alluvial diamonds found in the homonymous river