Geonomos is published by the Professor Manoel Teixeira da Costa Research Center, Institute of Geosciences, Federal University of Minas Gerais. Geonomos aims to increase communication between geoscientists by publishing original and unpublished articles of a technical-scientific nature in the fields related to Geology and Geosciences. Published since 1993, the journal's periodicity consists of two annual volumes.
Centro de Pesquisas Professor Manoel Teixeira da Costa - Instituto de Geociências da UFMG
The copyrights of the works published in Geonomos are those of the author, with rights of first publication for the journal.
ESTUDO DO POTENCIAL GEOTURÍSTICO DO PATRIMÔNIO MINEIRO DA SERRA DE OURO PRETO, SUDESTE DO QUADRILÁTERO FERRÍFERO, MG
The Ouro Preto and Mariana region, located in the southern portion of the Iron Quadrangle, Minas Gerais, hosted the nucleation of the ﬁrst urban centers in the central region of the state due to the Gold rush in the eighteenth century. The southern edge of the Mariana anticline had several gold mines that were closed after the end of the exploration of gold. Today, the region is an archaeological, historical, scientiﬁc and cultural record, closely associated with the local geology. This article aims the creation of a geoitinerary in the southern edge of the Mariana anticline, also named Ouro Preto Ridge, based on the inventory of the mining and geological heritage of the geosites of this region, done with the date gathering in ﬁeld visits. The mining galleries were highlight in this research, because they are classiﬁed as geosites according to parameters of touristic, social and environmental relevance. The visits to the geosites made the diagnostic of their situation about the heritage preservation and your relationship to touristic and environmental parameters possible. After the ending of this research, extension programs will be conducted with the local community in order to disseminate the importance of such geosites and their potential to promote a sustainable socio-economic development for the region. Therefore, through the promotion of research and extension programs involving the creation of a geoitinerary in the region, local communities can develop and rescue their identity, creating sustainable development mechanisms based on geotouristic practices. Keywords: Geoconservation; Mining Heritage; Georoute
SPELEOLOGICAL POTENTIAL OF THE SUMIDOURO STATE PARK / MG
Thematic mapping for the speleological potential of the Sumidouro State Park / mg. The Sumidouro State Park (PESU) constitutes a Conservation Unit located in the Environmental Protection Area (APA) Karst Lagoa Santa, between the municipalities of Lagoa Santa and Pedro Leopoldo, northern portion of the Metropolitan Region of Belo Horizonte, housing a rich speleological heritage. Currently, there are 49 known cavities registered in the database of the National Center for Research and Conservation of Caves (CECAV). It is estimated that there are more caves inserted in the park not yet registered by the agency. Thus, this work aimed to develop a predictive model in order to indicate areas with a higher potential for the occurrence of caves, in the light of geotechnologies. In order to perform the speleological potential calculation, data were collected on the existing features that are intrinsically linked to the formation of caves: geology, hydrography, exokarstic features present in the study area, hypsometry and slope. After data acquisition, values were assigned to them and, through map algebra, it was possible to identify areas with a higher and very higher degree of potential for the occurrence of caves. Because of the development of this model, it is expected that it will have application in other areas of study. Future ﬁeldwork should be carried out to conﬁrm and register new cavities pointed out in the mapped areas, especially those registered as having high potential. Keywords: karst; Apa; Lagoa Santa; speleological potential; multicriteria analysis.
A Pequena Idade do Gelo: evidências históricas e geológicas de mudança climática
Currently, basic school teachers are challenged to address climate control factors by means of an essentially interdisciplinary approach. This goes beyond developing an ability to manipulate scientiﬁc information from diﬀerent sources; it requires an understanding of the deep implications of scientiﬁc knowledge. This research has gathered evidence about the “Litlle Ice Age”, which occurred between the 16th and 19th centuries, when there was great cooling in the Northern Hemisphere, and other worldwide eﬀects. The database retrieved by the survey is divided as historical, geological, biological, geomorphological and artistic evidence, including knowledge about dating methods of the Quaternary ancient climates. The records help building a systemic understanding of the processes determining Holocene climatic variations. Ice ages can also be related to eustatic (sea level) variations. The results reveal the availability of diﬀerent paleoclimatic models, thus enhancing the implications of such extreme events for the societies. The models allow to identify some tendencies of climatic change, not perfectly convergent. Keywords: Paleoclimatology, Quaternary, Climate change, Environment, Geosciences.
Caracterização geológica-estrutural da conexão Araçuaí - São Francisco na área-tipo da Formação Rio Pardo Grande (Supergrupo Espinhaço, Minas Gerais)
In Serra do Espinhaço Meridional, the region between the districts of Rodeador (Monjolos) and Conselheiro Mata (Diamantina), in Minas Gerais, is located in the contact between the southeastern portion of the São Francisco Craton and the western portion of the Araçuaí Orogen. The Córrego Pereira and Rio Pardo Grande formations (Conselheiro Mata Group), Duas Barras Formation (Macaúbas Group), and Sete Lagoas, Serra de Santa Helena and Lagoa do Jacaré formations (Bambuí Group) outcrop in the area, besides metabasic Neoproterozoic dikes from the Pedro Lessa Suite that cut through the Espinhaço Supergroup units. The geological and structural characterization of the area was carried out, with emphasis on the Rio Pardo Grande Formation, top unit of the Espinhaço Supergroup, li le studied until then. The Rio Pardo Grande Formation was deposited in a marine platform and is constituted, at the base, by metarritmites, metapelites and ﬁne metarenites (Fácies Fl), with lenses of thick metarenite and metaconglomerate (facies Gsm), and metadolomites with stromatolytic structures at the top (Facies De). The registration of Facies Gsm metaconglomerates indicates the occurrence of a marine regression at the end of the deposition of the Conselheiro Mata Group, modifying the depositional model of the unit. The region's structuration is marked by expressive ductile and ruptile deformations developed during the Brasiliano Event, separated in two diﬀerent deformation phases. The main features are two large NNW-SSE axis anticlinals in the eastern portion of the area, a thrust fault of N-S direction and east dip forming a regional ramp-ﬂat context, regional wide open folds with west vergency and also considerable subvertical fractures oriented by WNW-ESE and NNW-SSE. The cinematic indicators in the region point out to mass transport form east to west. Keywords: São Francisco Craton, Araçuaí Belt, Rio Pardo Grande Formation, structural characterization
A Serra das Cambotas: terminação Meridional do Supergrupo Espinhaço no Quadrilátero Ferrífero, MG
The stratigraphic positioning of rocks grouped as Cambotas Formation (Quadrilátero Ferrífero, southeast of São Francisco Craton) has been the subject of discussion since its characterization in the 1960s. Our study provides structural and stratigraphic data of the Cambotas Formation, obtained in its type-section along with the Tamanduá and Cambotas mountain ranges, with the aim of deﬁning the stratigraphic-temporal relationships that characterize the Cambotas Formation and its surroundings. Also presents isotopic data (U-Pb in LA-ICP-MS) intended to shed light on the age of the unit, The large shear zone systems already described in the literature were observed, as well as the textural and sedimentological characteristics. The Cambotas Formation corresponds to a unit that groups together orthoquartzites and arcosian quartzites, whose basic stratigraphic relationship is controlled by tectonic contacts, through the Fundão-Cambotas Shear Zone System, and by the Córrego do Garimpo Fault. For provenance via U-Pb isotopic analysis in LA-ICPMS of detrital zircon grains, a sample collected from the Cambotas Formation in its type-section, in the homonymous mountain range, corresponding to ﬁne-grained orthoquartzite, in which 210-zircon grains collected and analyzed. The results indicate maximum sedimentation age during the Statherian, around 1755 ± 71 Ma, the peaks of ages between 1923 and 3010 Ma indicates a signiﬁcant contribution of Paleoproterozoic to Neoarquean sources. In the light of current stratigraphic knowledge, the peak of concordant analyzes with Statherian age (~ 1.7 Ga) discards the correlation between the Cambotas Formation and the Minas or Rio das Velhas supergroups. With this, we propose that the Cambotas Formation conﬁgure the southern termination of the Espinhaço Supergroup, corresponding to a restricted basin, with a multiplicity of source areas. This variety relates to the structural and stratigraphic complexity to which the northeastern region of the current Quadrilátero Ferrífero was subjected during its genesis. The sample provides an age similar to other works in the same area, validating the stratigraphic proposals presented. Keywords: Cambotas Formation, Quadrilátero Ferrífero¸ U-Pb Geochronology.
A MINERALOGIA DOS SOLOS TROPICAIS: ESTADO DA ARTE E RELAÇÃO COM O USO E MANEJO
The mineralogy of the tropical soils: state-of-the-art linked with land use and management. Part of the whole sorption and plant nutrition process are associated with the mineral matrix of soils. The goal of this study is to present a review of state-of-the-art about mineralogical characterization in the Brazilian tropical soils, in order to show details about soil genesis, as well as to analyze the mineralogy versus land use and management. In general, the understanding of mineralogy is necessary in tropical systems due to enormous quantitative, qualitative and geographic coverage of minerals constituting soils, especially in kaolinitic, oxydic (Fe) Latosols, and even gibbsites, besides those contained in Argisols and Cambisols, mainly. Thus, magnetite and maghemite could also have a greater a ention within soil classiﬁcation system due to a large occurrence in Brazilian soils and relationship between magnetic susceptibility and some management practices. In this way, classiﬁcation systems are prepared based on the knowledge and ordering from soil studies, including mineralogy, that directly aﬀect the management of agricultural areas, as well as those for environmental recovery and conservation. Keywords: Latosols (Oxisols); Iron oxides; Gibbsite; Kaolinite.
STRATIGRAPHIC AND STRUCTURAL RELATIONSHIPS THROUGH GEOLOGICAL AND GAMMAESPECTROMETRY ANALYSIS IN THE INTERFACE BETWEEN THE SÃO FRANCISCO CRATON AND THE ARAÇUAÍ OROGEN (SANTA RITA ANTICLINE, MINAS GERAIS, BRAZIL)
Geological mapping (1:25.000 scale), supported by gammaespectrometric analysis, was conducted in the Santa Rita Anticline region, a regional structure located in the contact between the Araçuaí Orogen external belt and the São Francisco Craton. The work aimed to detail the region's structural and stratigraphic relationships between the rocks of Espinhaço and São Francisco supergroups, which contact is not characterized by a thrust front, as it is in a large part of the Espinhaço Meridional Range (EMR). Five units from Espinhaço were mapped: Galho do Miguel Formation and Conselheiro Mata Group, represented by the Santa Rita, Córrego dos Borges, Córrego Bandeira and Córrego Pereira formations. By its turn, three units from the São Francisco Supergroup were mapped: undivided Macaúbas Group and Bambuí Group, represented by the Serra de Santa Helena and Lagoa do Jacaré formations. Restricted to the Espinhaço units, the Santa Rita Anticline consists in a structure with a south dipping axis and inﬂections that form saddle structures. The analysis of the gammaespectrometric responses provided clues that were conﬁrmed in the ﬁeld, highlighting an angular unconformity between the Córrego Pereira Formation and the Macaúbas Group and the local presence of isoclinal folds in Serra de Santa Helena rocks, promoting relevant questions regarding possible intermediary deformational events between the Statherian and Tonian tafrogenesis. The study contributes by raising questions about the evolution of the Araçuaí Belt in its contact with the São Francisco Craton and possible implications imposed by the Paramirim Keywords: Aerogeophysics, Litho-structural framework, Fold belt and craton transition, Espinhaço Meridional Range
DELINEAMENTO DE ÁREAS COM POTENCIAL EROSIVO PARA A BACIA HIDROGRÁFICA DO RIO PARANAÍBA (PN1-IGAM)
The identification of the erosive potential of area before it manifest it self of great importance to mitigate the risky circumstances and to avoid demages to the use of the ground. The aim of this work was to identify the áreas with the greatest potential to undergo erosive processes in the PN1 Hidrographic Basin (the Minas Gerais Water Management Institute divided the area of the Paranaíba River Basin in MG in PN1, PN2 and PN3). Through the use of Remote Sensing and Geographic Systems, the most sensitive áreas to na erosive process were identified, as wall as the manipulation of the variables inherent in this process, which operate in the basin. The soil types, land use, relief and other parameters required to understand erosion dynamics in the basin and calculated the Universal Soil Loss Equation (EUPS) for the diferente land use scenarios were evaluated. In order to obtain the results, erodibility and erosivity maps were elaborated to give an indication of the main areas of erosive risk in each use scenario. The results were presented for the erosive potential, were applied in a qualitative way, with the use and where they are not used conservationist practices. As a result, erodibility and erosivity maps were elaborated that allow the indication of the main áreas of erosive risk in each use scenario. Keywords: Basin Hydrographic; Soil; GIS; Soil Conservations; Erosion.
PRELIMINARY REPORT ON THE LACUSTRINE STRATA OF THE SANFRANCISCANA BASIN IN NORTHERN MINAS GERAIS, BRAZIL
We report new data on the geology and the fossil record of the Sanfranciscana Basin in sites to the north of the traditionally explored localities within Minas Gerais. The strata in the new explored area are formed by distinct lithologies, encompassing pelitic rocks with caliche levels and metric bodies of cross-bedded sandstone towards the top, similar to the ﬂuviolacustrine beds of the Areado Group in the southern portions of the basin. Also similar to other regions of the São Francisco Craton, the deposits of the Sanfranciscana Basin studied herein lie discordantly to the rocks of the Bambuí Basin. We preliminarily report neopterygian ﬁsh scales, little informative archosaurian bones and an association of the ostracods Ilyocypris- Fossocytheridea. This ostracod association is registered for the ﬁrst time in the Cretaceous of the Sanfranciscana Basin. The ostracods have been collected from the lacustrine, vertebrate-bearing rocks cropping out in Lagoa dos Patos and Coração de Jesus. The cytherideid Fossocytheridea assigns a minimal Aptian age to its bearing rocks. Its association with Ilyocypris was also reported in Upper Cretaceous oligohaline paleoenvironments in Brazil and Argentina, indicating similar depositional conditions to the strata reported in this paper. The putative aﬃnities of the specimens of the Sanfranciscana Basin with F. ventrotuberculata, and their association with Ilyocypris, raise the hypothesis of a younger age for some levels of that basin in northern Minas Gerais, perhaps ranging into the Late Cretaceous. Keywords: Ostracoda, Archosauria, Areado Group, Cretaceous, Gondwana
DEPÓSITOS DE QUARTZO AMETISTA EM MINAS GERAIS
In Minas Gerais State, quartz amethyst occurs in diﬀerent genetic geological environments. The present paper presents a review of the knowledge about such occurrences and deposits. Amethyst ﬁlling cavities in basalts, similar to those from southern Brazil, are restricted to Triângulo Mineiro region. Filled cavities are present at the upper portion of the central level of volcanic ﬂows and contain, besides quartz, minerals typically formed at low temperatures such as clay minerals and calcite. Hydrothermal vein deposits are mainly related to the Espinhaço Mountain Range and vicinities to east, showing a probable Brasiliano age, and represent the largest volumes in terms of related production and researches. They show amethyst associated mostly to hyaline or milky quartz and iron oxides. In pegmatites, amethyst is not very common, although occurrences close to Teóﬁlo Otoni are reported, besides the studied occurrence in Pancas (ES). This is situated within the context of the Eastern Brazilian Pegmatite Province, related to unzoned and little diﬀerentiated pegmatites which contain quartz, feldspar, muscovite, besides apatite, aquamarine and chrysoberyl. Keywords: Amethyst, Mineral Deposits, Minas Gerais State
GEOLOGIA APLICADA À GESTÃO E PLANEJAMENTO URBANO – ANÁLISE DE MULTICRITÉRIO DA PORÇÃO SUL DA MANCHA URBANA DE NOVA LIMA E HONÓRIO BICALHO
This paper shows the applied geology in urban areas, for geoenvironmental issues within human interaction with the physical environment. Those issues occur due to the lack of people knowledge and government planning about geological, morphological and hydrological features and their implication, putti ng those people into a vulnerability status. At this matter a Geoprocessing methodology of multicriteria analysis was used, allowing to synthesis results combined with many aspects. As an example were analyzed the urban expansion axis in the MG-30 highway between the south of Nova Lima city and Honório Bicalho district. Results indicate areas with susceptibility and vulnerability to risk of mass wasting due to the variables used in the modeling. The theme maps generated has the objective to support decision-making of the problems involved, for planning and mitigate risk inherent of the terrain, allowing an adequate interaction between urban expansion and physical environment. Keywords: Urban Geology. Geoprocessing. Multicriteria Analysis. Geological Risk. Decision-making.
RELAÇÃO HIDRÁULICA ENTRE O COMPLEXO BELO HORIZONTE E O GRUPO BAMBUÍ NA PORÇÃO SUL DA APA CARSTE DE LAGOA SANTA, MG
The hydraulic relation between Belo Horizonte complex and bambui group in the south portion of APA Carste de Lagoa Santa, mg. The area of this study is located north to the city of Belo Horizonte, Minas Gerais, has 432 km² and embrace the southern portion of the Federal Environmental Protection Area (APA) Carste de Lagoa Santa. The geology is characterized by the Belo Horizonte Complex in the basal portion, composed of granodiorites, granites and gneisses. Superimposed on this unit by tectonic contact, there are neoproterozoic rocks of the Bambuí Group, which from the bottom to the top are constituted by the Sete Lagoas Fm., composed of limestone, and the Serra de Santa Helena Fm., consisting of phyllites. Photointerpreted lineaments associated with structures measured in the ﬁeld and hydraulic data from tubular wells were used to determine the underground ﬂow between rocks from the Belo Horizonte Complex and from the Sete Lagoas Fm. From the speciﬁc capacity data, it was obtained that the NE direction is preferential for transferring water ﬂow from the fractures of the crystalline rocks to the supracrustal rocks of the Bambuí Group, from where the ﬂow preferably goes in the EW direction. However, the hydraulic productivity data collected show the productive ranges in the carbonate rocks are oriented preferentially in the N60-90E and N60-90W directions. Keywords: Apa carste de lagoa santa, hidrogeology, wells productivity
GLAUCONITA COMO FONTE ALTERNATIVA DE POTÁSSIO PARA PRODUÇÃO DE FERTILIZANTE DE LIBERAÇÃO LENTA
Glauconite (K₂(MgFe)₂Al₆(Si₄O₁₀)₃(OH)₁₂) is a monoclinic mineral, greenish, phyllosilicate hydrated of potassium and iron. It is an alternative source of potassium. This work investigated the dissolution of potassium in a solution of 2wt% citric acid after previous thermal and chemical processing with additives (CaCO₃, MgCl₂.6H₂O) of glauconita-bearing rock at six temperatures: 660°C, 700°C, 740°C, 780°C, 820°C and 860°C, 60 minutes and particle size less than 0.15mm. The mass ratio rock:CaCO₃:MgCl₂.6H₂O was: 1.0:0.2:0.3. For this purpose, a rock containing glauconite from the Cedro do Abaeté - MG, with 11.9% of K₂O and (58% of glauconita) was selected. The evaluation of potassium extraction was by carried out in citric acid 2wt% solution at 95°C for 15 minutes. The highest extraction of potassium (K) was 78% at the temperature of 770°C. The curve of extraction goes through a maximum (770°C), showing that there is a limit to the temperature in the thermal processing. Above this value there is a drop in the extraction indicating diﬀerent mechanisms of reaction between the rock and additives. Considering the range up to 770°C, thermal processing makes Verdete ore a potential alternative source of potassium for the production of long-term fertilizer. Keywords: Potassium; Verdete; Thermal Processing; Glauconite.
A GEOMORFOLOGIA DA SERRA DO ESPINHAÇO EM MINAS GERAIS E DE SUAS MARGENS
The geomorphological evolution of the Serra do Espinhaço is discussed based on: a) a critical analysisof previous papers about the geomorphology of the range, b) new interpretation based on own field data,c) regional interpretation, considering informations about the evolution of adjacent areas west and east ofthe range (São Francisco River, Doce River and Jeqitinhonha-Araçuaí Rivers Basins). The global contextis presented as a synthetical characterization of the main geological conditions, regional physiographyand drainage system organization and anomalies.The regional geomorphological organization is rigid controlled by the geology: a) the shape of therange reproduce the original collisional arc developed during the proterozoic orogeny, b) the existence oftwo strongly diferenciated plateaux (Planalto Meridional and Planalto Setentrional) reflect the litho-structuralcontrast between the southern and northern parts of the range, c) the morphology expresses the associationbetween lithological resistance to erosion and the tectonic organization in all scales.The morphology of the higher portions of the plateaux is characterized by relicts of two tertiaryplanation surfaces. They are probably peneplains resulting from erosion under tropical humid climaticconditions. During the Pleistocene, the valleys recorded the formation of several stepped terraces. thespacial variation on its dislevelments reflects the intensity of crustal uplifts and the position of the streamsin the drainage system hierarchy. The hillsides were, during the Upper Pleistocene, covered by two finecolluvial layers. In both cases, the cenozoic sediments register evidences of humid and hot paleoclimaticconditions.The Serra do Espinhaço acquired its present main physiography after the Miocene, which wascharacterized by tectonic stability. During the Pliocene, a strong compressional tectonic event reactivatedthe main precambrian thrust faults and detachment planes. As a consequence, the high scarp related to thewest thrust front was enhanced together with a eastward tilting of the plateaux. At the same time, in thePlanalto Setentrional, several valley heads of the São Francisco drainage basin were deviated and capturedby the Jequitinhonha Basin drainage system. In the Planalto Meridional, the geological conditions (porouslithology and anticline structure) favoured the capture of streams by the São Francisco Basin drainagesystem.As a consequence of the compressional forces that uplifted the range, an extensional stress fielddeveloped in the eastern border, generating grabens structures where the main rivers installed its valleys.The neotectonic activity is also recorded in several parts of the range and adjacent areas by normal, reverseand strike-slip faults in pleistocenic alluvial and colluvial deposits. Fault planes data analysis indicates ageneral NW-SE compressional stress field that remains up to the present time, as confirmed by results ofseismological data.(*)
DOTAÇÃO MINERAL, MEIO AMBIENTE E DESENVOLVIMENTO NO ALTO JEQUITINHONHA
The Alto Jequitinhonha region contains important mineral deposits wich have been known and exploitedsince the Brazilian colonial period. Despite this mineral potential, its population is one of the poorest inthe State of Minas Gerais. The extraction of ores is presently under much debate due to its complexrelationship with the environment and the regional development, particularly the Brundland report wichdefined guidelines for what is being called sustainable development. The situation is out of control on thepart of the government concerning such matters as mineral rights, payment of taxes and control andmonitoring of the environment. This scenario prevents the definition of public guidelines to allow theexploration of mineral resources such as diamond, gold, manganese, kyanite, chromite and other ores inregional projects. The first step must be taken by joint, articulated actions of the different federal, stateand municipal institutions to monitor, control and encourage mineral activities in the region. Such activitiescan act to enhance the generation of jobs and wealth, without neglecting the environment.
A MINERAÇÃO EM MINAS GERAIS: PASSADO, PRESENTE E FUTURO
The first Portuguese pioneers who entered the newly discovered Brazilian lands were not succesful inthe prospection of precious metals and stones. The primitive inhabitants were not enough cultivated toextract the metals from the rocks. They lived in the stone age yet. They became the sole valuable productof the “entradas” ventures. The mining in Brazil started when, in the end of the XVIII century, goldplacers were found in the lands which were later named Minas Gerais.The beginnings were terrible. The rich placers were depredated, the environment heavily spoiled byunskilled and thoughtless miners.The Portuguese royal authorities tried to recuperate the mining activities by sending to Minas Geraisthe German Metallurgical Technician, the baron W.L. von Eschwege who did a great effort to improve thegold and diamond mining works and to create alternative metallurgical undertakings.During the Imperial Times, several English ventures were organized to continue exploiting gold depositsin Minas Gerais. The majority failled being succesfull. English capital left Brazil when the South Africangold rush started in 1886.By 1910, American entrepreneurs tried to exploit the rich iron ore deposits found in the heart ofMinas Gerais state. Political controversy prevented the American from implanting the projected iron oreundertakings. Now, looking far back, some doubts remain about the feasibility of the proposed ventures.The year of 1934 marked important dates for the Brazilian mining legal structure. In 1942 werecreated the Companhia Vale do Rio Doce and the Companhia Siderúrgica Nacional.In the second half of the 1960 decade started the best times for the Brazilian mining, but by 1982 thepolitical and economical turmoils reverted the trend. Wild gold rush bursted out with great politicalsupport.In 1988 a constitutional assembly elaborated a new Charter in which foreign capital was forbidden tocontrol a mining company and the wild mining activities were deserved an encourageous treatment.Minas Gerais has always been in the heart of old mining history. This prominent position was affectedwhen the Carajás district came upon. Nobody may say this trend will be reverted.
A CORDILHEIRA DO ESPINHAÇO EM MINAS GERAIS: UM LEVANTAMENTO BIBLIOGRÁFICO
Este trabalho reúne as referências de artigos eresumos expandidos publicados, a partir de 1970, naRevista Brasileira de Geociências, nos anais dosCongressos Brasileiros de Geologia e nos anais dosSimpósios de Geologia de Minas Gerais, bem como nos anais do Simpósio sobre Sistemas Deposicionaisno Precambriano, realizado em 1987 em Ouro Preto.São ainda listadas teses de livre docência edoutoramento e dissertações de mestrado defendidasem universidades brasileiras e estrangeiras. Constam do levantamento um total de 274 referências, assimdistribuídas:Congresso Brasileiro de Geologia: 103 (37,6 %)Simpósio de Geologia de Minas Gerais: 64 (23,4%)Simpósio sobre Sistemas Deposicionais noPrecambriano: 4 (1,5%)Revista Brasileira de Geociências: 30 (11%)Teses e dissertações: 73 (26,6%)As teses e dissertações foram classificadas em doisgrupos, separando as que foram orientadas pelo Prof.Reinhard Pflug das de outros orientadores.Nos diversos grupos, os trabalhos foramorganizados por ordem cronológica. Para as referênciasde trabalhos anteriores ao ano de 1970 deve-se consultarPflug & Renger (1973), Renger (1979), Uhlein (1991)e Almeida Abreu (1993).As autoras agradecem aos professores AllaouaSaadi, Eduardo A. Ladeira e Friedrich E. Renger peloestímulo, incentivo e ajuda na confecção destacompilação.
RIFTEAMENTOS SUPERPOSTOS E TECTÔNICA DE INVERSÃO NA BORDA SUDESTE DO CRÁTON DO SÃO FRANCISCO
This paper presents a stratigraphical and structural study of the transition zone between São FranciscoCraton and Araçuaí Fold Belt in the Minas Gerais state. Two extensional events with rift formation andsedimentation and one orogenic event can be studied.The first extensional event was dated at 1750-1700 Ma. This event is represented by the N-S Espinhaçobasin formation in a continental rift. Its lower part (Early Sequence) is made of acid to intermediatemetavolcanics and fluvial metasediments, with strong fault-block activity in an initial rift phase (mechanicalsubsidence). The Middle Sequence is composed by quartzite with big cross-bedding and the Upper Sequenceconsists of an alternation of quartzite and metapelitic rocks deposited in a shallow marine setting in asubsequent flexural phase (with termal subsidence).The second extensional phase corresponded to Araçuaí rift formation (1000-900 Ma), with maficdikes swarm in the Espinhaço Supergroup. On the highest uplifted continental glaciogenic facies andglacio-marine sequence (Jequitaí Formation) was deposited. To east, in the Araçuaí basin, they grade intomarine deposits with gravitational sedimentation (debris-flow and turbidites) in a typical prism of passivecontinental margin. Westward, on the craton, the Bambuí Group lies directly on the basement. No equivalentshave been identified in the Araçuaí basin either they have not been deposited or are eroded.The orogenic event (650-550 Ma) is caracterized by zones with asymetric folds showing westwardsvergence separated by thin belts of ductile shearing ( Dp phase). N-S Sp cleavage with stretching lineationto east indicates a westward transport of materials toward the São Francisco Craton. The regional Barrowianmetamorphism is associated to Dp, increasing from anchizone to amphibolite facies. During this orogenicevent the São Francisco Craton and the Araçuaí and Paramirim Fold Belts were formed as individualgeotectonics units.
NOTA BREVE: CONSIDERAÇÕES PRELIMINARES SOBRE A EVOLUÇÃO CENOZÓICA DO CARSTE DE IRAQUARA, CHAPADA DIAMANTINA (BA)
A TAFROGÊNESE ESTATERIANA NOS BLOCOS PALEOPROTEROZÓICOS DA AMÉRICA DO SUL E PROCESSOS SUSEQÜENTES.
The Paleoproterozoic orogenic collages were very important for the origin of the older cratonic nuclei of the South American continent, with coalescence of various Archean blocks. Such fusion processes have been designated as the Transmazoninan Orogeny or Cycle, which is an oversimplification, because there were different (both in time and space) orogenetic events from 2.2 to 1.9 Ga (from the Rhyacian to the Orosirian period). Subsequent global process of taphrogenesis took place on the newly formed Paleoproterozoic landmasses- from Amazonia to Uruguay – with a striking synchronization, in the 1.8-1.7 Ga time interval (Statherian Period). These widespread extensional regimes were responsible for the evolution of different types of tectonic setting (including both magmatism and basinal sedimentation), starting from the preliminary branching systems of rifts within the post-Orosirian landmasses. Lithological assemblages for these periods/events, as well as they present records are variable within each occurrence. Felsic to intermediate volcanics (rhyolites, rhyodacites, dacites) and anorogenic A-type granites (and rare gabbro-anorthosite bodies) are the most commom, together with minor mafic dike swarms and mafic-ultramafic layered igneous intrusions. Some initial rift systems evolved to very large cratogenic basins, during an interval of hundreds of million years, with very typical quartzite-pelite-carbonate assemblages, of epicontinental seas and other continental environments. The age control for the upper sequences (Upper Mesoproterozoic) is still poor. There are several knows systems, in different cratonic blocks, from northern South America (Amazonia) to Uruguay and Argentina (Rio de La Plata craton) which will be mentioned. In all mentioned occurrences, there are a series of variables (geological and tectonophysical characteristics) still unknown. Relationships among time, heat flux and average factors of extension (β) cannot yet be estimated due to the scarcity of geochronological data. The only possibility for estimating the magnitude of those processes is through comparison of the intensity of the preserved geological records, keeping in mind their different crustal levels at present. Only small parts of these Proterozoic basins have remained as cratonic covers up to the present time. Some segments of them were first involved in collisional orogenic processes in Late Mesoproterozoic times (± 1.3 Ga), although geological records for this orogeny (so-called Uruaçuano) are still deficient. Additionally, most of these basins were involves in the fission of the Rodinia supercontinent, during the initial steps of the Brasiliano/Panafricano Cycle (around 1000 Ma) and many of their structural trends have been reactivated during the Neoproterozoic orogenic collage resulting in the agglutination of Western Gondwana. In such conditions, there are somes cases where the time interval is about 1.1 Ga from the basin-forming tectonics (Statherian Period) to the last period of orogenesis (c a 600 Ma, Neoproterozoic III). Sometimes, it is possible to observe along the same structural trends, or even side-by-side, both fold belts (Brasiliano domains0 and weakly deformed covers (on the Brasiliano cratonic blocks), with coeval volcano-sedimentary piles.
PERSPECTIVAS DO PROFISSIONAL DE GEOCIÊNCIAS EM UM CENÁRIO DE RETOMADA DE CRESCIMENTO ECONÔMICO BRASILEIRO.
The work market in Geoscience will be deeply affected when the Brazilian economic growth be restored. Economic and political decisions can promote changes on the present scenaries. From the environmental conscience it is emerging a new ethics trending to a companionship where Man is recognized as an integer part of Nature without to feel special. The main trends in Geosciences comprise two linked professional fields: (a) the development of infrastructure – including prospecting for oil, gas, water and minerals as well as activities stimulating the productive economic sectors – and (b) the preservation of life and related infrastructure. Both branches must answer quite fast to strategical decisions. They are complementary and aim to develop harmonious relationships between Man and the environment. So, it is useless to define any relative priority between them.
O CONGLOMERADO SAMBURÁ (GRUPO BAMBUÍ, NEOPROTEROZÓICO) E ROCHAS SEDIMENTARES ASSOCIADAS NO FLANCO LESTE DA SERRA DA PIMENTA, SW DE MINAS GERAIS: UM SISTEMA DE FAN DELTA.
In the southwest part of São Francisco Craton occur neoproterozoic metasedimentary rocks of the Bambuí Group. Among these rocks the Samburá Conglomerate outcrops nearby the external (eastern) region of the southernmost part of Brasilia Thrust Belt. Sedimentological studies carried on these rocks at Serra da Pimenta region reveals that they belong to a fan delta system developed at the toes of thrust fault escarpments of Brasilia Thrust Belt. Petrographic analysis of clasts of Samburá Conglomerate pointed to Canastra Group and Pium-í greenstone belt rocks of Serra da Pimenta mountains as source rocks. The fan delta deposits are rested above shallow marine carbonate rocks of the base of Bambuí Group.
GRANULITE FACIES ROCKS FROM GUAXUPÉ, MG: GNEISS-FLUID SEQUENCES AND P-T CONDITIONS
Gnaisses de fácies granulito nos arredores de Guaxupé formaram-se em condições de P-T estimadas em 8-9 Kb/800-900°C, e depois sofreram descompressão P-T-t em virtude dosoerguimento. O limite inferior deste caminho é estimado em 5-6 Kb/600-700°C. Estudos de inclusões fluidas mostram fluidos de CO2, N2 E H2O dentro dos vários tipos de rochas pertencentes a esta sequência gnáissica, que resultaram da evolução da região. As isócoras para o CO2 estão compatíveis com a estimativa do limite inferior de P-T, dentro do fácies anfibolito. Entretanto, nenhum pico de fase rica em CO2, dos fluidos metamórficos foi detectado, podendo ser que o metamorfismo aconteceu sob as condições de ausência de fluido. Efeitos de alteração incipiente induzidos por fluidos na paragênese de fácies granulitos sugerem que o fluido pode não ter sido pervasivo, como pé comumente assumido para os terrenos de fácies granulito.
CARACTERIZAÇÃO GEOTECTÔNICA DO SETOR SETENTRIONAL DO CINTURÃO RIBEIRA: EVIDÊNCIA DE ACRESÇÃO NEOPROTEROZÓICA NO LESTE DE MINAS GERAIS, BRASIL.
The early neoproterozoic evolution of eastern Minas Gerais is characterized by a history of a continental margin activity, including the accretion of suspect terranes. The Manhuaçu Terrane is one of those and is represented by a granitic continental plutonic arc and terrigeneous metasediments that reflect a continental margin. A metasedimentary gneiss belt at this margin with shallow to deep marine clastic lithologies as well as metavulcanic and metaplutonic mafic rocks was interpreted as an extensive tectonic segment with suspect development in a back-arc setting. Fragments of a volcanic arc are identified and interpreted as an evidence for a probable island-arc domain. In the studied region the Juiz de Fora and Paraiba do Sul Complexes are domains of these terranes. The distribution of magmatism in the studied region shows from west to east three different suites : 1) tholeiitic, 2) a medium to high-K cal-alkalic and 3) a high-K calc-alcalic/shoshonitic(?) magmatism which attests the evolution of early magmatism arcs (volcanic and plutonic) initially relates to ocean-plate subduction, followed by a continent-continent collision. Petrological, structural and geochemical data of mesoproterozoic/neoproterozoic metamorphic and magmatic suites of rocks are in agreement with the development of an accretionary orogeny. After a vulcanic-(island-arc) and a back-arc basin formation (by rifting of a continental margin with no spreading) in connection with eastward subduction, the island arc was accreted to a continental margin. Further subduction beneath it and a mechanism of flattening of the slab during the subduction process was responsible for the development of as granitic continental plutonic-arc (Andean-type batholith) eastwardly in a compressional setting. Continental plates became sutured and all intervening oceanic lithosphere was subducted beneath one of the converging masses. This resulted in the accretion of the Manhuaçu Microplate to the São Francisco Craton Domain. Plates continued to converge and the inversion of subduction polarity occurs resulting in a new subduction system (westward subduction) to the back of the Manhuaçu Microplate, in a easternward of the Espírito Santo state, with the establishment of a new magmatic arc of late neoproterozoic to eopaleozoic age. In this paper, only the probable early neoproterozoic volcanic (tholeiitic magmatism transitional between N-type MORB and island are basalts) and the plutonic (early continental calc-alkalic magmatism) arcs characterized by rocks with a very particular geochemistry and the back-arc basin setting will be discussed. Two alternative hypotheses to explain the evolution of these terranes may be postulated: 1) an island arc orogeny related to a westward subduction followed by a cordillerean type orogeny. With the advance of the island-arc and continent with offshore sediments, in different plates, a collision between these domains occurred. The old subduction zone was replaced by another one, eastward directed and the development of a continental magmatic arc occurred. Continental plates became sutured and all intervening oceanic lithosphere was subducted beneath one of the converging masses. Against this model are the presence of metavulcanic basic and intermediate rocks intercalated with marine and continental margin; 2) an extensional ensialic setting (aborted marginal basin) in the continental margin formed during the opening of a rapidly subsiding basin, with moderately rapid mantle upwelling, pronounced thinning of the continental crust and slight crustal contaminanton, without formation of oceanic crust or an island-arc may explain the association of basic metavulcanic rocks with marine and continental metasediments. Here, the low potassium contents of a few studied metavulcanic basic rocks and theire oceanic tholeiitic affinity are not well in agreement with this setting where continental basalts (flood basalts), or rocks ( basalts or basaltics andesites) belong to the high-K calc-alkaline series are expected to occur. Nevertheless, our evidences are not unequivocal enough for theire disapprovals.
ESTRATIGRAFIA DO SUPERGRUPO ESPINHAÇO NA REGIÃO DE PLANALTO DE MINAS, DIAMANTINA – MG.
In the region of Desembargador Otoni – Planalto de Minas (Northeastern Minas Gerais State, Brazil) two stratigraphics units of Precambrian age were recognized: the Espinhaço Supergroup and the Macaúbas Group. The metapelites of the Macaúbas Group (rhythmites with associated diamictites) represent varvites wuth dropstones which cover with a pronounced angular and erosional unconformity units of the Espinhaço Supergroup. This supergroup is divided in lithostratigraphic units. The Planalto de Minas Formation (at the base) is composed by a thick sequence of greenschists (originates from metabasalts) with variable composition and textures, locally with intercalations of thin quartzites and phyllites. The Tapera and Serra do Atalho formations are built up by laminated, micaceous meta-arenites and pure or micaceous meta-arenites, normally with cross bending. Respectively. Intercalations of phyllites and greenschists occur in both units, in addition the Serra do Atalho Formation contains also hematitic phyllite and a thin intercalation of metarhyolite. This volcanic, volcanoclastic, and clastics units were deposited in a basin related to the initial phase (at about 1750 Ma) of crustal extension of the Espinhaço Rift.
SIGNIFICADO DA OCORRÊNCIA DE FOSFATOS E BORATOS DE ALUMÍNIO NO CONTATO ENTRE OS SUPERGRUPOS RIO PARAÚNA E ESPINHAÇO NA REGIÃO DE DIAMANTINA, MINAS GERAIS, BRASIL
Within a muscovite-kyanite quartzite and/or muscovite-kyanite schist at the contact between the UpperArchean Barão de Guacuí Formation and the Bandeirinha Formation near Diamantina (State of MinasGerais, Brazil) five rock types defining mineral assemblages can be found: 1: lazulite, kyanite, 2: lazulite,augelite, kyanite; 3: lazulite, amblygonite, tourmaline; 4: lazulite, svanbergite, tourmaline, and 5:dumortierite, kyanite. Additional phases in all rock types are quartz and muscovite/sericite. The wholerock chemistry influences the chemical composition of the individual minerals.These ocurrences are interpreted as precipitation of aluminium, phosphorous and boron-rich sedimentaryrocks in highly alcaline lakes under sabka conditions in the Middle Proterozoic on the Archeanmetasediments of the Baraõ de Guacuí Formation.During the Brasiliano event (680-450Ma) a greenschist metamorphism and associated tectonism withthrusting the actual texture and foliation were formed. Mobilization of lazulite and its deposition intoquartz veins, cutting the over- and underlain units occurred, too.The aluminophosphate minerals get importance because they could help to define more precisely thecontact between the Rio Paraúna and Espinhaço supergroups.
COMPOSIÇÃO QUÍMICA DE CROMITAS EM CORPOS METAMÁFICO/ ULTRAMÁFICOS DA BORDA LESTE DO ESPINHAÇO MERIDIONAL, MINAS GERAIS
The study of variation in chemical composition of chromites associated with mafic/ultramafic sequenceshas a growing in importance because presents a close relation to gold and platinum group elementsconcentration. The researched areas : Serro, Alvorada de Minas and Morro do Pilar present chromites(massive, disseminated and accessory), which show a strong zoning due to hydrotermal/metamorphicprocess. These zones reflect changes in chemical composition of crystals, which are related to neoformationof mineral paragenesis based mainly on leaving of the elements in chromites ( for example the origin ofkammererites).In chromitites from Serro and Alvorada de Minas, as well as in accessory chromites from Morro doPilar, the zoning of the grains was observed. They have a core composed by chromites (aluminous chromites)and a broad margin with ferriferous composition (chromium magnetites to magnetites). In same cases thechromite crystals have a core with primary chemical composition preserved. In the Rio Mata Cavalovolcano-sedimentary sequence a Ir-Pt alloy was found as inclusion in chromium-magnetite. In othersmafic/ultramafic complex of Minas Gerais and Ceará States, high relations of PGE and Au has beenrecorded, and they are associated with chromitites submitted to this alteration process.
EVOLUÇÃO CLIMÁTICA DO GONDWANA NA REGIÃO CENTRO-SUL DO BRASIL E SEUS REGISTROS GEOLÓGICOS CONTINENTAIS DURANTE O MESOZÓICO, ENFATIZANDO O ARCO DO PARANAÍBA, A BORDA NNE DA BACIA DO PARANÁ E A PORÇÃO MERIDIONAL DA BACIA SANFRASCISCANA, NO OESTE DO ESTADO D
Current theories suggest the the main cause of the temperature changes in Earth surface along thegeological time, seems to be, as a concensus, the anomalous concentration of CO2 , CH4 and other gasesin the terrestrial atmosphere. There are however divergences about the origin of these gases which are themain responsables for the greenhouse effect.This study discusses questions about the global climate changes in the geological past, commentingthe mass-extinction periods of the Permian-Triassic (P/Tr) and Cretaceous/Tertiary (C/T) boundaries. Therelationship between unusual high CO2 levels in the atmosphere and mass-extinction events is commented.The origin of the greenhouse gases are attributed to: a) extensive outgassing of volatiles through of largevolcanic events, or b) asteroid or cometary impact by bodies ranging up to 10 Km in diameters, or c)marine and terrestrial organic production by living organisms.Climatic changes have been detected in all the geological records, from Precambrian to Cenozoic.Tillites and varvites in Gondwana are features of Proterozoic and Paleozoic ice ages. The Mesozoic, onthe other hand, had a global warm climate, exhibiting generally high level sea and low thermal variationbetween the poles and the equator. The Mesozoic continental geologic records in Gondwana are consequenceof this arid climate, and the sedimentary rocks are mainly red-beds seguences or other related with arid/semi-arid environments.The relationship between the climate, geological records and paleogeographical aspects in the MesozoicCentral-South Gondwana are presented, focussing the NNE border of the Paraná and the SouthernSanfranciscana basins, which occur in the western part of Minas Gerais state. The Parecis Basin thatoccurs in Mato Grosso State is also mentioned.These basins show sequences of varied rock types -volcanicand sedimentary ones -, and exhibit ages ranging from early to late Cretaceous.Other important paleogeographic feature studied occurs as a strip of intensely deformed Precambrianrocks forming a NW-SE tectonic arch, preserved as a succession of thrust slices. This is known as Alto doParanaíba Arch or Alto do Paranaíba Anteclesis, (Ladeira et al. 1971, Grossi Sad et al 1971, respectively),a regional structure related with the emplacement of the Cretaceous Paraná and Sanfranciscana basins.
O PAPEL DO ANTEPARO NA MODELAGEM FÍSICA DE CINTURÕES COMPRESSIVOS – UM ESTUDO APLICADO A UM DUPLEX DO TIPO PILHA ANTIFORMAL
In order to analyze the effect of a moving wall on experimental thrust systems, the progressive evolutionof antiformal stacks was simulated in sandbox models. The rigid, acrylic moving wall was substituted byanalogue material. Different boundary conditions demonstrated that in physical models the use of thehabitual stiff wall obstructs the development of the real architecture of compressional tectonics.
UM MODELO PARA A EVOLUÇÃO MICROESTRUTURAL DOS MINÉRIOS DE FERRO DO QUADRILÁTERO FERRÍFERO. PARTE II – TRAMA, TEXTURA E ANISOTROPIA DE SUSCEPTIBILIDADE MAGNÉTICA
Low strain itabirite still displays primary features similar to jaspilites such as sedimentary layeringand a porous granoblastic fabric composed of martite with magnetite relics and hematite Due tosynmetamorphic deformation this mineralogy recrystallizes in specularite producing a variety of fabrics,textures and anisotropy of the magnetic susceptibility (AMS) depending mainly on the strain conditions.Folded ores usually display a foliation parallel to the banding due to flexural slip and an axial planeschistosity that results in a lepidogranoblastic fabric. The stereogram of the {11.0} texture is a singlemaximum parallel to the intersection lineation. The AMS is low and its ellipsoid is triaxial. Increasingstrain and shearing transposes and obliterates the primary banding, resulting in iron ore mylonites withlepidoblastic (S-tectonites) or nematoblastic (L-tectonites) fabrics probably depending on the shape of thestrain ellipsoid.The stereogram of the {11.0} texture of schistose ores is typically a girdle parallel to foliation. AMSintensity is high with oblate shape. Stereograms of the texture of lineated ores display a single maximumparallel to the stretch lineation. AMS is low to moderate with prolate shape. Secondary recrystallizationand grain growth does not affect the lattice preferred orientation.