The Granulite-Facies Rocks of the Northern Segment of the Ribeira Belt, Eastern Minas Gerais, SE Brazil     

Antonio Gilberto Costa   《Gondwana Research》1998,1(3-4):367-372

Granulite rocks are exposed in eastern Minas Gerais, Brazil. Its early neoproterozoic evolution is characterised by a history of an active continental margin, including the accretion of suspect terranes. The Manhuaçu Terrane is one of those which is represented by a granitic continental plutonic arc and terrigeneous metasediments reflecting a continental margin. A metasedimentary gneiss belt at this margin with shallow to deep marine clastic lithologies as well as metavolcanic 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. The granulites occur as massive rocks as well as high-grade gneisses and show lithological, structural and metamorphic attributes consistent with their host belt type. In the western portion granulites derived from sedimentary protoliths, have been deposited, deformed and metamorphosed together with the mafic intrusions and as well as with their crystallization. Regional uplift exposed these rocks probably immediately after the metamorphism. In these belts the metamorphic grade is not uniform, especially where uplifting has exposed oblique cross sections over the granulitic rocks. Geothermobarometric calculations indicate that the granulites has been generated under T conditions between 800 and 990 ± 50 C and from medium (4.8 kb) to relatively high (10.0 kb) pressures.  相似文献   

Magma convection and mixing dynamics as a source of Ultra-Long-Period oscillations     

Antonella Longo  Paolo Papale  Melissa Vassalli  Gilberto Saccorotti  Chiara P. Montagna  Andrea Cassioli  Salvatore Giudice  Enzo Boschi 《Bulletin of Volcanology》2012,74(4):873-880

Many volcanic eruptions are shortly preceded by injection of new magma into a pre-existing, shallow (<10 km) magma chamber, causing convection and mixing between the incoming and resident magmas. These processes may trigger dyke propagation and further magma rise, inducing long-term (days to months) volcano deformation, seismic swarms, gravity anomalies, and changes in the composition of volcanic plumes and fumaroles, eventually culminating in an eruption. Although new magma injection into shallow magma chambers can lead to hazardous event, such injection is still not systematically detected and recognized. Here, we present the results of numerical simulations of magma convection and mixing in geometrically complex magmatic systems, and describe the multiparametric dynamics associated with buoyant magma injection. Our results reveal unexpected pressure trends and pressure oscillations in the Ultra-Long-Period (ULP) range of minutes, related to the generation of discrete plumes of rising magma. Very long pressure oscillation wavelengths translate into comparably ULP ground displacements with amplitudes of order 10⁻⁴–10⁻² m. Thus, new magma injection into magma chambers beneath volcanoes can be revealed by ULP ground displacement measured at the surface.  相似文献   

Erosion of an active fault scarp leads to drainage capture in the Amazon region,Brazil          下载免费PDF全文

Pedro Val  Clauzionor Silva  David Harbor  Norberto Morales  Felipe Amaral  Tiago Maia 《地球表面变化过程与地形》2014,39(8):1062-1074

Far from the continental margin, drainage basins in Central Amazonia should be in topographic steady state; but they are not. Abandoned remnant fluvial valleys up to hundreds of square kilometers in size are observed throughout Amazonia, and are evidence of significant landscape reorganization. While major Late Miocene drainage shifts occurred due to initiation of the transcontinental Amazon River, local landscape change has remained active until today. Driven either by dynamic topography, tectonism, and/or climatic fluctuations, drainage captures in Amazonia provide a natural experiment for assessing the geomorphic response of low‐slope basins to sudden, capture related base‐level falls. This paper evaluates the timing of geomorphic change by examining a drainage capture event across the Baependi fault scarp involving the Cuieiras and Tarumã‐Mirim River basins northwest of the city of Manaus in Brazil. A system of capture‐related knickpoints was generated by base‐level fall following drainage capture; through numerical modeling of their initiation and propagation, the capture event is inferred to have occurred between the middle and late Pleistocene, consistent with other studies of landscape change in surrounding areas. In low‐slope settings like the Amazon River basin, base‐level fall can increase erosion rates by more than an order of magnitude, and moderate to large river basins can respond to episodes of base‐level fall over timescales of tens to hundreds of thousands of years. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Community structure and functional traits of mollusks associated with coastal reef macroalgae in Northeastern Brazil     

Dbora Ferreira Barbosa  Thelma Lúcia Pereira Dias  Srgio de Faria Lopes  Rafaela Cristina de Souza Duarte  Fernanda Maria Duarte do Amaral 《Marine Ecology》2019,40(5)

This study investigated the community structure and functional traits of the mollusk fauna associated with macroalgae with different thallus morphologies in a reef environment in Northeastern Brazil. A total of 15 individuals of each species of macroalgae adhered to natural substrate and 15 individuals of Padina gymnospora detached from the substrate were collected. The structural complexity of algal habitats was measured and the associated malacofauna screened and identified. All three macroalgae differed significantly in the complexity of their habitat, with Sargassum polyceratium being the most complex. A total of 823 specimens of mollusks belonging to 22 species and 11 families were recorded, of which Columbellidae was the most represented with six species. The functional trait “size” revealed that micromollusks smaller than 10 millimeters were predominant in the community; however, individuals of larger sizes (up to 24.54 millimeters) belonging to young stages of other species were also present. Eight functional trophic groups were identified, of which “carnivorous” stood out with seven species. Six functional groups of microhabitats were identified, with intra‐specific variation in habitats, while habitat expansion was documented for species not yet recorded in association with macroalgae. The structure of the molluskan community differed among the three algae species with the greatest richness, abundance, and diversity of mollusks and functional traits occurring with S. polyceratium. Community structure differed between algae adhered to natural substrate and detached algae, with the latter having lower mollusk richness and diversity, but with greater abundance of some species that remained on algal fronds after release from the reef environment. This study reinforces the importance of algal habitat for marine invertebrate fauna, especially for micromollusks that spend their entire life cycle, or part of it, in association with macroalgae.  相似文献   

Geoweb Services for Sharing Modelling Results in Biodiversity Networks   总被引：1，自引：0，他引：1  

Karla Donato Fook  Antônio Miguel Vieira Monteiro  Gilberto Câmara  Marco Antônio Casanova  Silvana Amaral 《Transactions in GIS》2009,13(4):379-399

Biodiversity researchers in different institutions deal with predictive models for species distribution. These models are useful for biodiversity conservation policies. Species distribution modelling tools need large datasets from different sources and use many algorithms. To improve biodiversity science, scientists need to share models, data and results, and should be able to reproduce experiments from others. This article presents a geoweb service architecture that supports sharing of modelling results and enables researchers to perform new modelling experiments. We show the feasibility of the proposed architecture by developing a set of prototype services, called Web Biodiversity Collaborative Modelling Services – WBCMS. They provide a set of geospatial web services that support the sharing of species distribution models. The article includes an example of a model instance that explains the WBCMS prototype. We believe that WBCMS shows how to set up a cooperative research network on biodiversity research.  相似文献   

Relics of eclogite facies assemblages in the Ceará Central Domain, NW Borborema Province, NE Brazil: Implications for the assembly of West Gondwana   总被引：1，自引：0，他引：1  

Ticiano J. Saraiva dos Santos  Maria da Glria M. Garcia  Wagner Silva Amaral  Renauld Caby  Eberhard Wernick  Michel H. Arthaud  Elton L. Dantas  M. Santosh 《Gondwana Research》2009,15(3-4):454-470

The Borborema Province, in the NE of Brazil, is a rather complex piece in the Brazil–Africa puzzle as it represents the junction of the Dahomeyide/Pharusian, Central African, Araçuai and Brasilia fold belts located between the West-African/São Luis, Congo/São Francisco and Amazonas craton. The correlation between the Dahomeyides from W-Africa (Ghana, Benin, Togo, and Mali) and the Borborema Province involves the Médio Coreaú and Central Ceará domains. The inferred continuation of the main oceanic suture zone exposed in the Dahomeyides of W Africa is buried beneath the Phanerozoic Parnaíba Basin in Brazil (northwest of the Médio Coreaú domain) where some high density gravity anomalies may represent hidden remnants of an oceanic suture. In addition to this major suture a narrow, nearly continuous strip composed of mainly mafic pods containing relics of eclogite-facies assemblages associated with partially migmatized granulite-facies metapelitic gneisses has been found further east in the NW Borborema Province. These high pressure mafic rocks, interpreted as retrograded eclogites, are located between the Transbrasiliano Lineament and the Santa Quitéria continental arc and comprise primitive to evolved arc-related rocks with either arc- or MORB-type imprints that can indicate either deep subduction of oceanic lithosphere or roots of continental and oceanic magmatic arcs. Average peak P–T conditions under eclogite-facies metamorphism (T = 770 °C and P = 17.3 kbar) were estimated using garnet–clinopyroxene thermometry and Jd content in clinopyroxene. Transition to granulite-facies conditions, as well as later widespread re-equilibration under amphibolite facies, were registered both in the basic and the metapelitic rocks and suggest a clockwise P–T path characterized by an increase in temperature followed by strong decompression. A phenomenon possibly related to the exhumation of a highly thickened crust associated with the suturing of the Médio Coreaú and Central Ceará domains, two distinct crustal blocks separated by the Transbrasiliano Lineament.  相似文献   

Spatial data availability and its implications for sustainable development of the Brazilian Amazon   总被引：1，自引：0，他引：1  

Silvana Amaral  Julio Cesar Lima D’Alge 《Earth Science Informatics》2009,2(4):193-203

In the Amazonia region, general policy based on sustainable development must be adopted to counterbalance natural conservation and the needs of people. To discuss and monitor the regional development requires a significant variety of spatial data. However, making data available is not simple and various solutions usually are presented in non-standardized and non-interchangeable databases. This paper presents an overview of spatial data available for the Amazonia region, and initiatives of data dissemination systems, considering various geographical scales and data access. From this general perspective, we discuss some ideas about the importance of spatial data for sustainability and suggest interactive systems that could contribute to local development and environmental conservation. The limitation on the promotion of spatial information and data sharing in Amazonia is neither computational nor technological. Rather, it is a matter of informing those who generate the data about the benefits of knowledge as a public good and promoting collaborative work. Creating a convergent spatial consciousness about the territory, and bringing together every environmental player, is a step towards the discussion and planning of the sustainable development of the Amazonia.  相似文献   

Gilthead seabream (Sparus aurata) carrying antibiotic resistant enterococci. A potential bioindicator of marine contamination?     

Barros J  Igrejas G  Andrade M  Radhouani H  López M  Torres C  Poeta P 《Marine pollution bulletin》2011,62(6):1245-1248

Antibiotic resistance in bacteria is a growing problem that is not only restricted to the clinical setting but also to other environments such as marine species that harbor antibiotic resistant bacteria and therefore may serve as reservoirs for antibiotic-resistance genetic determinants. The aim of this study was to evaluate antibiotic resistance phenotypes in enterococci isolated from fecal samples of gilthead seabream and the associated mechanisms of resistance. A collection of 118 samples were analyzed and 73 enterococci were recovered. The strains showed high percentages of resistance to erythromycin and tetracycline (58.9% and 17.8%, respectively). Lower level of resistance (<13%) was detected for quinupristin-dalfopristin, ampicillin, high-level-gentamicin, high-level-streptomycin, high-level-kanamycin, ciprofloxacin and chloramphenicol. The erm(B), tet(L) or tet(M), aac(6′)-aph(2″) and aph(3′)-IIIa genes were shown in isolates resistant to erythromycin, tetracycline, high-level gentamicin and high-level kanamycin, respectively. Antibiotic resistance in natural microbiota is becoming a concern of human and environmental health.  相似文献   

On the Effect of Thermally Induced Stresses in Failures of Some Rock Slopes in Rio de Janeiro, Brazil   总被引：1，自引：0，他引：1  

Euripedes do Amaral Vargas Jr.  Raquel Quadros Velloso  Leonardo Erik Chávez  Luiz Gusmão  Claudio Palmeiro do Amaral 《Rock Mechanics and Rock Engineering》2013,46(1):123-134

Previous studies have indicated that many rock slope failures in Rio de Janeiro, Brazil, occur during relatively dry periods when there is little, if any, rainfall. In the present paper, we describe these events and propose possible mechanisms for their occurrence. It is believed that daily fluctuations in temperature may create thermally induced stresses of enough magnitude to propagate fractures already existing in the rock mass. Laboratory experiments were conducted in order to measure temperature variations in a fractured rock system. Using the experimentally obtained data, we carried out numerical analyses in order to verify whether temperature-related stresses were indeed able to propagate fractures existing in the rock mass. The results obtained indicate that cycles of temperature change over time, especially during the colder months of the year can indeed create stress conditions in the rock mass able to propagate existing non-persistent joints, and ultimately lead to failure of the rock slope.  相似文献   

Occurrence of shallow cold flows in the winter atmospheric boundary layer of interior of Alaska     

Gilberto J. Fochesatto  John A. Mayfield  Derek P. Starkenburg  Matthew A. Gruber  James Conner 《Meteorology and Atmospheric Physics》2015,127(4):369-382

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