Minas Gerais State Research Articles

A new bluish-leaved Syagrus (Arecaceae) from an overlooked OCBIL in the Espinhaço Range (Brazil)

Background and aims – This study is part of ongoing research on the Arecaceae Flora of the Serra do Cabral, an isolated massif in the southwest of the Espinhaço Range in Minas Gerais State. Because of the isolation of the massif, the area has a rich biodiversity and a high level of endemism. While searching for populations of the rare and critically endangered Syagrus cabraliensis, a new bluish-leaved palm species was discovered and it is described here. Material and methods – The new species’ morphology is described based on field collections. The pinnae were analysed using SEM and LM cross- and longitudinal sections following default methodology. In addition, we compared the species to S. cabraliensis and provided ecological notes and a conservation status assessment. Key results – Syagrus carvalhoi resembles S. cabraliensis but they can easily be distinguished by morphoanatomical characters. Both species occur non-sympatrically in the Serra do Cabral, in contrasting microhabitats: S. carvalhoi in the southern quartzitic campos rupestres and S. cabraliensis in the northern ferruginous campos rupestres. A key to the known grass-like Syagrus species from the massif is provided. Based on the restricted area of occurrence and the anthropogenic threats, Syagrus carvalhoi is assessed as critically endangered. Conclusion – Syagrus carvalhoi is the second grass-like endemic Syagrus species from the Serra do Cabral and presents rare characters within the genus (grass-like aspect, colonial habit, flowers in tetrads, and the stem forking at or below the ground). This discovery corroborates that this isolated OCBIL is a home for endemic and rare palm species. The Serra do Cabral massif has proved a source of morphological and anatomical novelties in Arecaceae, affecting the taxonomy and understanding of the evolution and ecology of palms. Our results reinforce the notion that it is important to conserve this area with rich and rare biodiversity but under alarming and unprecedented threats.

Geology of amethyst quartz deposits from Montezuma and surrounding areas of Minas Gerais and Bahia States

Amethyst quartz deposits occur in some regions of Minas Gerais state, Brazil, related to different geological environments. The most important are associated with hydrothermal veins crossing the Espinhaço mountain range, mainly in small and eroded mountains near its east margin, related to the Macaúbas Group. In the border region between the states of Minas Gerais (MG) and Bahia (BA), some of these deposits produce amethyst crystals that become green under heat treatments and are known in the gemmological market as “prasiolite.” The aim of the present study was to provide details of the clear structural control over the mineralized veins. The quartz veins are hosted in quartzites, which have long been the subject of controversy regardingtheir stratigraphic position. In this study, they are inserted into the Santo Onofre (MG) and Serra de Inhaúma (BA) sequences of unknown ages. These quartzites show a folded subvertical foliation, indicating a posterior deformational phase that had not been observed in rocks from the Macaúbas Group in other regions of MG state. At the Montezuma mine (MG), the main veins are around 0.70-1.10 m thick with steep dips to the NE, perpendicular to the NE-SW foliation; bedding orientation is approximately N-S, dipping to the E. In the Coruja mine area (BA), host quartzites have foliation attitudes varying between N35-45°E/ subvertical, and mineralized veins are around 1 m thick, nearly concordant with the foliation. At Tibério’s mine (BA), the mineralization is related to narrow fractures, less than 30 cm wide, and perpendicular to the host quartzite foliation, with directions/dips around N20°W/80°SW. In described deposits, amethyst veins occur structurally related to axial surfaces in foliation folds.

Partial characterization of Loxosceles anomala (Mello-Leitão, 1917) venom: A brown spider of potential medical concern

The spider's genus Loxosceles (also known as “brown spiders”) is one of the few ones of medical importance in Brazil, being Loxosceles anomala a species of common occurrence in the Southeast region. This species is usually smaller in size than the other members of the Loxosceles group. A single human accident involving L. anomala was reported to date and the clinical picture shared similar characteristics with accidents caused by other Loxosceles species. Despite the potential relevance of L. anomalafor loxocelism in Minas Gerais state, its venom activity has never been characterized. In this work, we provide a preliminary characterization of L. anomala venom, considering its most relevant enzymatic activities and its venom immunorecognition by current therapeutic antivenoms. The results showed that L. anomala venom is immunorecognised by therapeutic antivenoms and by anti-phospholipase D antibodies. Its venom also shows enzymatic activities (sphingomyelinase activity, fibrinogenolytic) described for other Loxosceles venoms. This work contributes to a better knowledge on the venom content and activities of synanthropic Loxosceles species that have the potential of causing relevant human accidents.

Ethno-zootechnics from the perspective of dairy farmers in the brazilian cerrado

Considering the valuable environmental and cultural heritage existing in the world in the context of agribusiness, it is possible to highlight the role of ethno-zootechnics as an important new tool for understanding these values, the rescue and generational transmission of livestock knowledge are relevant. Given this, the objective was to understand the perception of milk producers from the Ethno-zootechnical perspective. Through a semi-structured script, questionnaires were carried out with 41 interviewees and representatives of dairy farms to register the relevance of basic cultural knowledge associating them with social, economic and social environmental development. Cluster analysis was carried out using the hierarchical method. It was concluded that part of the dairy farmers located in the Northwest region of Minas Gerais state, the man/animal relationship is important, with traits of affection and utility. The transmission of traditional knowledge of the dairy activity is important, and that they believe that scientific and traditional knowledge can be beneficial in rural activity.

Struggling over Serra do Curral

The Serra do Curral is a mountain range that extends to the municipalities of Belo Horizonte, Sabará and Nova Lima, in Minas Gerais state, Brazil. It is already deteriorated by a long history of mineral extraction not followed by any environmental restoration. Since the 1960’s, Serra do Curral has been an object of many civil society collective actions calling for its preservation. In 2022, the authorization of new mining operation provoked a strong civil society reaction. A coalition of environmental and social activists, alongside new political actors convened in defence of Serra do Curral now demand the immediate revocation of the licence. The present article analyses the current conflict, identifying the main actors, their collective action repertoires, and how those actions play out as the conflict unfolds. The research is conducted through documental inquiry, media coverage analysis and on-site direct observation. Looking into the political struggle around new-extractivism conflicts, we argue, can provide important data and insights about resistance and the developing of alternatives.

Yield prediction in banana (Musa sp.) using STELLA model

To overcome the challenges encountered in banana cultivation, such as the high cost of production due to high water consumption by the banana plant, efficient management practices are being adopted. The use of agricultural forecasting techniques is an alternative that has been gaining attention in rural areas. One way to manage and improve agricultural productivity is the use of technologies that allow the monitoring of production. The implementation of computational tools as software to aid processes, such as irrigation management, is gradually taking up space in the agricultural sector. In this light, herein, the present study aimed to develop a model using STELLA 8.0 software to estimate the growth and productivity of irrigated banana (Musa sp.). For this, the physiological processes and water demand were calculated using reference evapotranspiration (ET0) and culture evapotranspiration (ETc) in the first banana cycle for the climatic conditions of the Jaíba Project (Jaíba, Minas Gerais State, Brazil). The data of the climatic conditions were obtained from the National Institute of Meteorology. It was verified that the average monthly ET0 was 5.78 mm day-1. In addition, the water requirement of the plant corresponded to a blade equivalent to 65% of ET0. The verified productivity was 8.93 t ha-1, which is considered adequate for the simulated conditions. The model responded efficiently to the proposed application and was characterized as a prognostic tool of reality through simplified representation.

Geology, geochemistry, and mineralogy of saprolite and regolith ores with Nb, P, Ba, REEs (+ Fe) in mineral deposits from the Araxá alkali-carbonatitic complex, Minas Gerais state, Brazil

The Araxá Complex is a significant source of mineral deposits, including Nb, P, Ba, LREE, and Fe. These deposits are formed by weathering phlogopite-rich rocks and norsethite carbonatite in the Complex core and from the weathering of carbonatites in the surrounding ring. The main types of ore in the Complex include rust-colored, brown, and orange ore. The rust-colored ore contains over 2% CaO and MgO and is mineralized with pyrochlore, barite, and fluorapatite in the phlogopititic core and only fluorapatite in the carbonatitic ring. Brown ore has less than 2% MgO and over 2% CaO and is mineralized with pyrochlore, barite, fluorapatite, and magnetite in the core and only fluorapatite in the ring. Orange ore has less than 2% MgO and CaO and is mineralized with pyrochlore, barite, monazite, and magnetite in the core and goyazite in the ring. Pyrochlore and iron minerals were concentrated from the rock to the orange ore, while fluorapatite was concentrated from the rock to the brown ore. The weathering of fluorapatite in orange ore leads to the formation of authigenic gorceixite, goyazite, and monazite. The neogenesis of barite in the Complex occurs due to the dissolution of norsethite, followed by the chemical bonding of Ba with S from sulphuric solutions. The ore deposits are up to 200 m thick, stratiform, and horizontal, formed by meteoric water that flowed vertically downwards, then horizontally, radially, and centrifugally. The weathering of 100 m of rock resulted in the formation of approximately 33 m of orange ore, 9 m of brown ore, and 4 m of rust-colored ore in the Complex core and 35 m of orange ore, 7 m of brown ore, and 10 m of rust-colored ore in the carbonatite ring. Lake sediments accumulate on the orange regolith top surface.

High prevalence of intermediate resistance to ciprofloxacin in Salmonella enterica isolated from a Brazilian poultry production chain, located in Minas Gerais state

We characterized the distribution and diversity of antimicrobial-resistance Salmonella enterica isolated from a poultry production chain in Minas Gerais, Brazil, with special attention to ciprofloxacin and multidrug resistance (MDR). S. enterica (n = 96) of different serotypes and from different processing steps were subjected to broth dilution assay to estimate the minimum inhibitory concentration (MIC) for 12 antibiotics (8 classes) and screened using PCR for the presence of 17 antimicrobial-resistance genes. Isolates presented mainly resistance to ampicillin (11/96), and most presented intermediate resistance to ciprofloxacin (92/96). Roughly one-third (33/96) were resistant to streptomycin based on our interpretive criteria. Most strains resistant to streptomycin and ciprofloxacin were PCR-positive for aphA (51/96) and qnrB (94/96), respectively. Ciprofloxacin resistance was further investigated through high-resolution melting qPCR (HRM-qPCR) and sequencing of quinolone resistance-determining region (QRDR: gyrA, gyrB, parC, and parE). Minor differences were identified in melting temperatures (Tm), and a Thr57Sr mutation was observed in parC. MDR isolates harboring acrA and capable of expressing the AcrAB-TolC multidrug efflux pump were resistant to ethidium bromide at 0.4 mg/mL. The intermediate resistance to ciprofloxacin may be associated with qnrB, and the potential role of Thr57Ser mutation warrants further investigation. The high prevalence of antibiotic related genes and its association with the observed intermediary resistance to ciprofloxacin indicates the widespread of this hazard in the studied poultry production chain.

Multispectral images for estimating morphophysiological and nutritional parameters in cabbage seedlings

Remote sensing data have been used to monitor numerous agricultural crops, but few studies have used low-cost multispectral sensors to assess biometric, nutritional and physiological parameters in a cabbage crop, especially in seedlings. As such, this study aimed to estimate the biometric variables of cabbage using parametric and non-parametric models based on the response of multispectral images taken by a multispectral camera. The experiment was conducted in a greenhouse in the municipality of Uberaba, Minas Gerais state (MG), Brazil. Twenty days after sowing (DAS), multispectral images of the plants were captured using a MAPIR Survey 3 camera. To compose the estimation models, the multispectral vegetation indices were calculated based on the original calibrated bands. Multispectral cameras can be used to estimate biometric, physiological, and nutritional variables in cabbage crops. Among the Mapir camera bands, B660 exhibited the greatest variability, showing that the red range was the most sensitive to the different treatments. Except for leaf area, all the parameters measured could be estimated by linear models, with deterministic coefficients of up to 72%. Although neural network models provided more accurate estimates, the maximum quantum yield of photosystem II (Fv/Fm) was most accurately estimated (1.2%) by the linear model generated by algorithm M5.

Cytogenetic Analysis of the Fungus-Farming Ant Cyphomyrmex rimosus (Spinola, 1851) (Formicidae: Myrmicinae: Attini) Highlights Karyotypic Variation

The fungus-farming ant genus Cyphomyrmex (subtribe Attina, clade Neoattina) comprises 23 described species that are widely distributed throughout the Neotropics. Species within Cyphomyrmex have taxonomic issues such as Cyphomyrmex rimosus (Spinola, 1851) which is likely a species complex. Cytogenetics is a useful tool for evolutionary studies and understanding species with dubious taxonomy. In this study, we characterized the karyotype of C. rimosus from Viçosa, Minas Gerais State, southeastern Brazil using classical and molecular cytogenetic techniques to enrich the chromosomal information about Cyphomyrmex. The karyotype of C. rimosus from the rainforest of southeastern Brazil (2n = 22, 18m + 4sm) notably contrasts with that previously described for this species in Panama (2n = 32). This intraspecific chromosomal variation suggests the existence of a species complex within this taxon according to the previous hypothesis derived from morphological analysis. We detected GC-rich heterochromatic regions in C. rimosus and, using repetitive DNA probes, showed that this heterochromatin shares repetitive sequences with other Neoattina species already studied, enhancing the importance of this specific genome region in the understanding of Attina evolution. Mapping of microsatellite (GA)₁₅ on C. rimosus was restricted to the euchromatic regions of all chromosomes. The single intrachromosomal rDNA sites observed in C. rimosus follow the general genomic organization trend of ribosomal genes in Formicidae. Our study extends the data of chromosome mapping on Cyphomyrmex and reinforces the importance of cytogenetic studies in different localities to better understand taxonomic issues in widely distributed taxa such as C. rimosus.

Spatio-temporal visualization and forecasting of {text {PM}}_{10} in the Brazilian state of Minas Gerais

Air pollution due to air contamination by gases, liquids, and solid particles in suspension, is a great environmental and public health concern nowadays. An important type of air pollution is particulate matter with a diameter of 10 microns or less ({text {PM}}_{10}) because one of the determining factors that affect human health is the size of particles in the atmosphere due to the degree of permanence and penetration they have in the respiratory system. Therefore, it is extremely interesting to monitor and understand the behavior of {text {PM}}_{10} concentrations so that they do not exceed the established critical levels. In this work, we will study the {text {PM}}_{10} concentrations in all available monitoring stations in the Brazilian state of Minas Gerais. To better understand its behavior, we will provide a spatio-temporal visualization of the {text {PM}}_{10} concentrations. Besides the descriptive and visualization analysis, we consider six standard and advanced time series models that will be used to fit and forecast {text {PM}}_{10} concentrations, with application to three locations, one in Belo Horizonte, the Minas Gerais state capital, and the monitoring stations with the lowest and highest average {text {PM}}_{10} concentration levels.

American visceral leishmaniasis in an ecotourism area

Visceral Leishmaniasis is a vector-borne disease that represents one of the most important public health problems in the world. This neglected tropical zoonosis shows an increasing urbanization process, since the end of the 1980s. The increase in ecotourism practices, mainly in regions nearby urban areas facilitates the interaction between companion animals, humans, and wildlife. Known as the land of the waterfalls, Carrancas is a 728 km² Brazilian municipality located at 1052m, in the southeast of Brazil. The region is surrounded by urban areas with autochthonous cases of Canine Visceral Leishmaniasis and lacking studies on the presence of vectors of Leishmania spp. The municipality is part of the most important ecotourism area, a renowned tourist destination in Brazil and abroad called Royal Road or “Estrada Real – ER. Due to the increasing number of travelers involved in ecotourism and exposing them to risk factors for diseases, we propose to investigate the presence of phlebotomine sandflies in a protected area in the southern state of Minas Gerais, which is constantly visited by tourists over the world. Six specimens of Lutzomyia longipalpis were captured in Carrancas. This is the first report of L. longipalpis in an ecotourism area south of Minas Gerais State. This record contributes to our knowledge of the geographical distribution of the main vector of American Visceral Leishmaniasis in Carrancas and alerts us to the need for permanent surveillance and health education at this location.

Stigmatodon enigmaticus (Bromeliaceae, Tillandsioideae), a new lithophytic species from the Campos Rupestres within the Brazilian Atlantic Forest

Stigmatodon enigmaticus is described and illustrated as a new lithophytic taxon from the quartzitic Campos Rupestres within the biodiversity hotspot of the Atlantic Forest, in Minas Gerais state, Southeastern Brazil. This puzzling new species presents floral features that are unique in the genus as they are associated with ornithophily, as in most Vriesea, contrasting with the chiropterous features of all previously known Stigmatodon species. It is assigned to the “S. limae group”, being most similar to S. vexatus, with which it is compared. Stigmatodon enigmaticus is a microendemic species and is here assessed as Critically Endangered due to its restricted habitat, reduced population size, and threats from invasive species. This finding adds to several others that reinforce the relevance of the currently unprotected Serra do Padre Ângelo as a priority for conservation.

Multicentre surveillance of epidemiologically important pathogens causing nosocomial bloodstream infections and pneumonia trials in Brazilian adult intensive care units.

Introduction. Healthcare-associated infections (HAIs) are the most recurrent adverse event in hospitals worldwide and represent an important public health problem.Gap statement. There are a paucity of multicentric data describing severe HAIs such as bloodstream infection (BSI) and pneumonia in Brazil.Aim. To provide an up-to-date picture of the extent and patterns of HAIs in adult intensive care units (ICUs), as well as to identify variables associated with the risk of development of severe infections.Methodology. Point prevalence surveys were conducted using standardized protocols in 35 ICUs from Minas Gerais state, Brazil. Medical records of eligible inpatients at or before 8 am on the survey day were reviewed to identify HAIs present at the time of the survey. A matched-pairs case-control study was performed on a total of 66 pairs for BSI and 115 pairs for pneumonia according to the selection criteria developed.Results. Overall, 171 patients (45.7%) had at least one HAI, with most (78.4%) acquired in the ICU. These patients presented a total of 240 infections; including 123 pneumonia (51.3%) and 66 BSI (27.5%), and 78.9 and 80.3 %, respectively, were acquired in the ICU. Their aetiology showed a predominance of Gram-negative bacteria versus Gram-positive bacteria (48.9 versus 43.3 %), with Acinetobacter baumannii (13.7%) and Pseudomonas aeruginosa (12.8%) being prominent. One striking observation from our data was the higher prevalence of Staphylococcus aureus (14.5%) and coagulase-negative staphylococci (10.2%) observed in the overall HAIs.Conclusion. A high severe ICU-acquired HAI burden was found when compared with findings from other low- and middle-income countries. These data can be utilized for better planning of nosocomial infection surveillance programmes in our hospitals.

A Framework for Geoconservation in Mining Landscapes: Opportunities for Geopark and GEOfood Approaches in Minas Gerais, Brazil

The continuous processes of mining development, since the very beginning of Minas Gerais State’s development, have been giving new attention and meaning to valuable pre-existing features (i.e., cultural, social, and physical-environmental), impacting and recharacterizing not only its municipalities but their essential local or native sociocultural components. At the same time, mining, as one of the central pillars of the Brazilian development model, has put different communities, natural and cultural heritage, and mineral and water resources at risk. The wide concept of geodiversity and the related geoheritage emerge as an alternative for conservation, territorial planning, and sustainable development, to reconcile these spheres. This study developed a comprehensive framework for geoconservation within selected areas of mining landscapes, contributing to insights for the creation of a catalog about geoheritage in the state of Minas Gerais, discussing and analyzing well-established strategies and opportunities based on UNESCO Global Geoparks (UGGp) and the GEOfood brand. We concluded that the mining landscapes of Minas Gerais must be administered as a viable possibility for economic and environmental dynamic actions and activities, strengthening the maintenance of municipalities from the very beginning to after the end of operational activities. Heritage programs such as UGGp and GEOfood enable knowledge sharing and engagement with geoheritage, improving the comprehension and management of the short- and long-term impacts of mining, while elevating geodiversity as a major source of information in the “greening” of mining policies.

Chusquea calderoniae (Poaceae: Bambusoideae), a new species of C. subg. Chusquea endemic to the Espinhaço Range, Brazil

Chusquea is the richest genus of Neotropical bamboos, occurring from Mexico to Argentina and Brazil, with 198 accepted species. In Brazil, 49 members of this genus have been recorded, with the Eastern region being its main center of diversity, especially in the states of Bahia, Minas Gerais, and Rio de Janeiro. The Espinhaço Range, found within this region, is considered the largest mountain complex in Brazil, including campo rupestre, caatinga, and cerrado vegetation types and transitional types among these, which explains the particular plant diversity of this region. Our recent taxonomic studies on Brazilian Chusquea subg. Chusquea indicated the presence of a new species herein described and illustrated, named C. calderoniae. It is morphologically related to the C. meyeriana informal group, being most similar to C. attenuata, but differing by the shape of the central bud and the length of the spikelet structures. The new species is endemic to the Espinhaço Range, occurring in riparian forest on the flanks of Pico das Almas, Chapada Diamantina, Bahia, and the Diamantina Plateau in Minas Gerais state, associated to campo rupestre vegetation, in contrast to C. attenuata, which occurs in the Atlantic rainforest in the states of Minas Gerais and Rio de Janeiro.

A new species of Megalobulimus from the early Holocene of southeastern Brazil (Gastropoda: Strophocheilidae)

A new species of megasnail, Megalobulimus diluvianus sp. nov., is herein described based on subfossil material from limestone caves in the area of Lagoa Santa, Minas Gerais state, southeastern Brazil. The specimens come from a context of archaeological strata of early Holocene age. Considering the morphological features of the shell, the new species seems closely allied to the so-called “Megalobulimus bronni complex”, whose representatives inhabit the tropical to subtropical Atlantic plateau of southeastern Brazil. Megalobulimus diluvianus sp. nov. is considered to be presently extinct (substituted by M. oblongus in the stratigraphical record).

Two noteworthy Calea (Asteraceae: Neurolaeneae) from contact areas of the Atlantic Forest and Cerrado of Brazil

Systematic studies in the Calea myrtifolia complex have revealed two noteworthy new taxa from the contact, relict and transitional areas of the Atlantic Forest and Cerrado domains in Brazil: Calea grandiflora and Calea × parviantha, both having been treated as C. myrtifolia, now considered endemic to Minas Gerais state, Brazil. Thus, we herein provide morphological descriptions, illustrations, geographical distribution maps and discuss their taxonomic affinities. Moreover, their potential distributions are predicted. Calea grandiflora is related to C. arachnoidea and is recognized by the basal acrodromous venation (vs. semicraspedodromous), outer phyllary series 12.2–20 × 4.2–10.6 mm long (vs. 9–12 × 3–5 mm), and ray floret corolla 16.9–31 mm long (vs. 10–12 mm). Calea × parviantha is a new nothospecies, supported by a unique set of character states partially shared with the parental species C. parvifolia and C. triantha. The new hybrid species has intermediate morphology, as demonstrated by a multivariate analysis. It differs from C. parvifolia by the hispid, hispidulous or glabrous stems (vs. puberulous or puberulent) and coriaceous leaves (vs. chartaceous leaves), and from C. triantha by the rounded leaf base, sometimes subcordate (vs. cordate) and pappus scales 1.1–2.7 mm long (vs. 0.8–1.3 mm). Furthermore, we provide a taxonomic key for Calea in the states of São Paulo and Paraná.

Strategies to improve the competitiveness of an agroindustrial system for a macauba based oil production in Minas Gerais State, Brazil

The Macauba palm has been studied because of increasing global interest in multipurpose resilient plants, with no food or energy competition. The crop encompasses an opportunity to social inclusion, profitable activity and environmental care in Brazil. However, for its production to be competitive, it demands a deeper analysis of how the Agroindustrial System (AIS) is currently organized and what is needed to go forward. The objectives of the present study were to characterize and evaluate the competitiveness of macauba AIS at the main Brazilian production region, the north of Minas Gerais State. Stakeholders engaged in fruit picking and processing segments were identified and characterized. In addition, strategic actions to strengthen this AIS were proposed. The framework used to evaluate the competitiveness of the AIS includes data gathering from field interviews, direct observations and analysis of the macauba AIS. Some challenges were picked from the direct observations such as the reliance of production on unfavourable environmental conditions, the deficiencies in technical assistance and the difficulty of farmers to access credit and public policies. Despite those hurdles, the examined AIS showed potential to expand and become competitive, promoting better conditions for the permanence of family farmers/ communities in the countryside. It is important to consider that macauba exploitation is getting to a point of transition from extractive activity to a systematized planting of the palm. Some strategies to boost this growth are better coordination among the agents acting in the AIS, establishment of more active R&D and technical assistance partnerships, capacity building/ training offerings, and provision of resources for investments intended for the sustainable development of the macauba AIS and market access.

KOMATIITE LAVAS FROM THE QUEBRA OSSO GROUP (RIO DAS VELHAS GREENSTONE BELT, SOUTHEAST BRAZIL): A FIELD GUIDE TO AN ARCHEAN FLOW FIELD

The Quebra Osso Group encompasses one of the best preserved Archean komatiite flows in the Quadrilátero Ferrífero region, southern São Francisco craton (Brazil). It is commonly associated with the base of the Rio das Velhas greenstone belt within the Santa Bárbara tectonostratigraphic block. The Quebra Osso rocks are well exposed along the valley of the homonymous river, near the Catas Altas city (Minas Gerais state), and in inactive serpentine quarries. In this field guide, we provide the descriptions of the key outcrops in this area, including a variety of komatiite flows, sedimentary rocks and pyroclastic rocks. Despite the pervasive alteration of primary mineral assemblages due to greenschist to amphibolite facies metamorphism, the ultramafic rocks exhibit diverse igneous textures and structures. Volcanic textures are recognizable due to the morphology of the original igneous olivine and pyroxene, which underwent pseudomorphosis by hydrous minerals – serpentine and chlorite. These features include distinctive spinifex and cumulate textures that provide clues of the conditions operating during emplacement and crystallization of the ultrabasic liquids. The predominance of thick-packages of massive flows suggests channelized lava flows, with subordinate thin marginal layered (spinifex-textured), pillowed, brecciated and pyroclastic flows. Volcanic breccias, pillow lavas and chemical sedimentary rocks indicate that these rocks erupted underwater. These multiple volcanic products characterize a unique komatiite flow field and their remarkable preservation distinguishes the Quebra Osso Group from the other ultramafic associations within the São Francisco Craton.