Petrogenesis of early paleozoic peralkaline rhyolites from the Macedo de Cavaleiros region (NE Portugal)     

M. Luisa Ribeiro 《International Journal of Earth Sciences》1987,76(1):147-168

The petrology and geochemistry of Variscan peralkaline gneisses from NE Portugal, discovered in 1962, is presented. Major and trace element data for the oversaturated sequence of the Macedo de Cavaleiros area depict some specific geochemical patterns: high Fe₂O₃ ^(t) (even higher than in the Ethiopian Main Rift), high REE concentrations and small Eu anomalies. Field and petrographical observations also suggest that liquid immiscibility has played an important petrogenetic role in the crystallization trends. The alternating pyroxenefeldsparhematite-rich bands observed in outcrop are interpreted as resulting from fluctuating fO₂ conditions. Petrological and geochemical data show that these pantelleritic and comenditic rocks are the end members of an alkaline-transitional basaltic sequence, by which they are overlain. An uppermost sequence of oceanic tholeiitic basalts completes the picture of an evolving rift environment, where mantle processes generate crustal thinning and eventually oceanic crust.

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Zusammenfassung Petrologie und Geochemie variszischer peralkaliner Gneisse aus Nordostportugal, 1962 entdeckt, werden dargestellt. Die Haupt- und Spurenelementanalysen dieser übersättigen Gesteine weisen Besonderheiten auf, wie z. B. die hohen Fe203-Gehalte, die selbst noch die des »Ethiopian Main Rift« übersteigen, die hohen Konzentrationen an Seltenen Erdelementen und die kleine negative Eu-Anomalie. Geländegeologie und Petrographie suggerieren, da\ die liquid-magmatische Entmischung eine wichtige petrogenetische Rolle im Kristallisationsablauf spielte. Im Aufschlu\ wird eine Wechsellagerung von Pyroxen-Feldspat- und Hämatit-reichen Schichten beobachtet, die hier als Folge von fO2-Schwankungen erklärt wird. Die petrologischen und geochemischen Daten zeigen, da\ die pantelleritischen und comenditischen Gesteine die letzten Glieder in einer Abfolge vom alkalinen übergangstyp darstellen... Die vulkanische Abfolge im Gebiet von Macedo de Cavaleiros endet mit tholeiitischen Basalten, die damit das Bild der magmatischen Entwicklung in einem Rift-Bereich, in dem Mantelprozesse eine Krustenverdünnung in einem Rift-Bereich, in dem Mantelprozesse eine Krustenverdünnung und die Bildung ozeanischer Kruste bewirkten, vervollständigen.

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Résumé L'auteur présente la pétrologie et la géochimie des gneiss varisques peralcalins du nord-est du Portugal, découverts en 1962. Les analyses des éléments majeurs et en traces dans ces roches sursaturées montrent quelques caractéristiques spéciales comme la haute teneur en Fe₂O₃ (t) (supérieure mÊme à celles de l'»Ethiopian Main Rift«), la haute concentration en terres rares et la faible anomalie négative de Eu. La géologie de terrain et les observations pétrographiques suggèrent aussi que l'imiscibilité entre liquides a joué un rÔle pétrogénétique important au cours de la cristallisation. Les alternances de bandes alternativement riches en pyroxène-feldspath et en hématite, observées sur les affleurements, sont interprétées comme le résultat de la fluctuation de fO₂. Les données pétrologiques et géochimiques montrent que les roches pantéléritiques et comenditiques représentent les derniers termes d'une séquence du type alcalintransitionel qui les surmonte. La séquence volcanique dans le secteur de Macedo de Calvaleiros se termine par des basaltes tholéiitiques qui complètent le cadre d'une environnement d'un zone de »rift« dans laquelle les processus mantéliques ont déterminé l'amincissement crustal et la formation d'une croûte océanique.

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Morphology of the Itapeva to Tramandai transgressive dunefield barrier system and mid‐ to late Holocene sea level change     

Patrick A. Hesp  Sergio Rebello Dillenburg  Eduardo Guimaraes Barboza  Luiz C. P. Clerot  Luiz J. Tomazelli  Ricardo Norberto Ayup Zouain 《地球表面变化过程与地形》2007,32(3):407-414

The surface morphology of the transgressive dunefield barrier extending from Itapeva to Tramandai along the northern littoral of Rio Grande do Sul, is examined and an attempt is presented to link morphological changes across the barrier to Holocene sea level changes. The 4·5 km wide Holocene barrier displays two typical morphologies: an inner part dominated by large‐scale, continuous alongshore, overlapping dunefield phases comprising sand sheets, dunes, deflation plains and precipitation ridges; and an outer part dominated by discontinuous, medium‐ to small‐scale, triangular to lobate transgressive dunefield phases, cut by both active and relict (palaeo‐) creeks or washouts. Holocene sea level in the region rose to c. +1 to +3 m above present reaching a maximum around 5100 years bp and then progressively fell to the present level. We argue that the effect on barrier development was to suppress the development of a drainage system during the rising and maximum stages, and encourage the development of an organized drainage system in the form of regularly spaced washouts during the falling period, and that this change in sea level from rising to falling therefore produced the large‐scale differences in barrier morphology. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

The Present, Past, and Future Contributions to Global Warming of CO2 Emissions from Fuels     

Luiz Pinguelli Rosa  Suzana Kahn Ribeiro 《Climatic change》2001,48(2-3):289-307

The objective of this paper is to emphasize theresponsibility of developed countries to implement the Climate Convention, as well as the role ofdeveloping countries in CO₂ emissions controlwhile sustaining their rights to increase energyconsumption per capita during the development process. Itis shown that the growth in CO₂$ emissions fromfossil fuel consumption in North America, excludingMexico, from 1990 to 1996 was 3.7 times higherthan that of Latin America in absolute terms. Thecumulative contribution to global warming, expressedas the mass of the gas multiplied by time (GtCy), can becalculated as the integration of the atmosphericconcentration of the emitted gas along time, witha weight function in the integrand to simulate theclimate response. To simulate climate response,we used the superposition of exponential decay functions with different decay constants. Thehistorical contributions of the OECD countries,the Eastern European countries and theex-Soviet Union, and from all developingcountries are considered. The future contributionsare computed in three scenarios. All of them showthat emissions from Non-Annex I countrieswill become higher than those of Annex I countriessoon after 2010, while the curves of atmosphericconcentration will cross one another later, not muchbefore 2050, and the respective contributions toglobal temperature increase will cross about 2090.  相似文献   

Brazil's premier gold province. Part II: geology and genesis of gold deposits in the Archean Rio das Velhas greenstone belt, Quadrilátero Ferrífero     

Lydia Lobato  Luiz Ribeiro-Rodrigues  Frederico Vieira 《Mineralium Deposita》2001,36(3-4):249-277

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Comment on ‘The fast Hankel transform’ by A.A. Mohsen and E.A. Hashish1     

Luiz Rijo 《Geophysical Prospecting》1996,44(3):473-477

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The energy balance experiment EBEX-2000. Part II: Intercomparison of eddy-covariance sensors and post-field data processing methods     

Matthias Mauder  Steven P. Oncley  Roland Vogt  Tamas Weidinger  Luis Ribeiro  Christian Bernhofer  Thomas Foken  Wim Kohsiek  Henk A. R. De Bruin  Heping Liu 《Boundary-Layer Meteorology》2007,123(1):29-54

The eddy-covariance method is the primary way of measuring turbulent fluxes directly. Many investigators have found that these flux measurements often do not satisfy a fundamental criterion—closure of the surface energy balance. This study investigates to what extent the eddy-covariance measurement technology can be made responsible for this deficiency, in particular the effects of instrumentation or of the post-field data processing. Therefore, current eddy-covariance sensors and several post-field data processing methods were compared. The differences in methodology resulted in deviations of 10% for the sensible heat flux and of 15% for the latent heat flux for an averaging time of 30 min. These disparities were mostly due to different sensor separation corrections and a linear detrending of the data. The impact of different instrumentation on the resulting heat flux estimates was significantly higher. Large deviations from the reference system of up to 50% were found for some sensor combinations. However, very good measurement quality was found for a CSAT3 sonic together with a KH20 krypton hygrometer and also for a UW sonic together with a KH20. If these systems are well calibrated and maintained, an accuracy of better than 5% can be achieved for 30-min values of sensible and latent heat flux measurements. The results from the sonic anemometers Gill Solent-HS, ATI-K, Metek USA-1, and R.M. Young 81000 showed more or less larger deviations from the reference system. The LI-COR LI-7500 open-path H₂O/CO₂ gas analyser in the test was one of the first serial numbers of this sensor type and had technical problems regarding direct solar radiation sensitivity and signal delay. These problems are known by the manufacturer and improvements of the sensor have since been made. The National Center for Atmospheric Research is supported by the National Science Foundation.  相似文献   

Occurrence and Resistance of Pathogenic Bacteria Along the Tietê River Downstream of São Paulo in Brazil     

Wolf-Rainer Abraham  Alexandre José Macedo  Luiz Humberto Gomes  Flavio C. A. Tavares 《洁净——土壤、空气、水》2007,35(4):339-347

The load of pathogenic bacteria, their fate and their dangerousness in the Tietê River were assessed along 100 km starting from the city of São Paulo, Brazil. The data were compared with those from two German rivers. High loads of pathogens were found in the Tietê River near the city of São Paulo (Escherichia coli O157:H7, Shigella flexneri, and Shigella boydii), which were absent 30 km downstream of São Paulo. The antibiotic resistances observed in the Tietê river were rather low and decreased after the major input in São Paulo to significantly lower levels about 30 km downstream. While the Brazilian isolates were more susceptible for ampicillin than the German ones, the reverse was observed for gentamycin. For optimal control of infections in humans critical areas where these bacteria survived longer and their elimination mechanisms should be identified as well as the extent and the origin of antibiotic resistance should be determined.  相似文献   

Comparison of the SFI peculiar velocities with the IRAS 1.2-Jy gravity field     

Luiz N. da Costa  Adi Nusser  Wolfram Freudling  Riccardo Giovanelli  Martha P. Haynes  John J. Salzer  & Gary Wegner 《Monthly notices of the Royal Astronomical Society》1998,299(2):425-432

We present a comparison between the peculiar velocity fields measured from a recently completed l -band Tully–Fisher survey of field spirals (SFI) and that derived from the IRAS 1.2-Jy redshift survey galaxy distribution. The analysis is based on the expansion of these data in redshift space using smooth orthonormal functions, and is performed using low- and high-resolution expansions, with an effective smoothing scale which increases almost linearly with redshift. The effective smoothing scales at 3000 km s⁻¹ are 1500 and 1000 km s⁻¹ for the low- and high-resolution filters. The agreement between the high- and low-resolution SFI velocity maps is excellent. The general features in the filtered SFI and IRAS velocity fields agree remarkably well within 6000 km s⁻¹. This good agreement between the fields allows us to determine the parameter β = Ω^0.6 / b , where Ω is the cosmological density parameter, and b is the linear biasing factor. From a likelihood analysis on the SFI and IRAS modes we find that β = 0.6 ± 0.1, independently of the resolution of the modal expansion. For this value of β, the residual fields for the two filters show no systematic variations within 6000 km s⁻¹. Most remarkable is the lack of any coherent, redshift-dependent dipole flow in the residual field.  相似文献   

Extensional tectonics in the Gorringe Bank rocks, Eastern Atlantic ocean: evidence of an oceanic ultra-slow mantellic accreting centre     

Girardeau  Cornen  Beslier  Le Gall  Monnier  Agrinier  Dubuisson  Pinheiro  Ribeiro  & Whitechurch 《地学学报》1998,10(6):330-336

The Gorringe Bank corresponds to an upper mantle peridotite ridge enclosing a 500-m thick/ 50-km long laccolith-like body of gabbro, locally cut and poorly covered by tholeiitic rocks. Strain and kinematic analysis of orientated gabbros and peridotites sampled during the GORRINGE diving cruise (1996) provides new kinematic constraints on extensional high-temperature deformation recorded at deep levels during stretching, near an accreting centre axis of a mantle-dominant oceanic lithosphere. It is argued that the Gorringe Bank lithosphere formed at an oceanic ultra-slow, N010°–020°-trending accreting centre, mostly by passive tectonic denudation of the mantle, without any synchronous large magmatism. This peculiar lithosphere may be representative of the Iberia oceanic domain located between the continent and the J anomaly ridge, which likely marks the beginning of true spreading at an oceanic spreading ridge.  相似文献   

Land use dynamics in Brazilian La Plata Basin and anthropogenic climate change     

Ana Carolina F. de Vasconcelos  Sandro L. Schlindwein  Marcos A. Lana  Alfredo C. Fantini  Michelle Bonatti  Luiz R. D’Agostini  Sergio R. Martins 《Climatic change》2014,127(1):73-81

The La Plata Basin (LPB) is one of the most important regions for agriculture and livestock production in South America, playing a central role in the world food production and food security. Within its borders is also located the whole Brazilian Pantanal region. Identifying the most important land use sectors in LPB as well as the changes observed in the past years is fundamental to recognize which areas of the basin might be more vulnerable to climate change in order to design adaptation strategies. A general characterization of land use and livestock production of Brazilian LPB was done by using the System of Automatic Retrieving (SIDRA) of Brazilian Institute of Geography and Statistics (IBGE) platform as the major source of data. It was observed expressive increases in land areas used for temporary crops, such as soybean, sugarcane, and maize, as well as increases in poultry and swine production. These important changes in agricultural land use and livestock production are currently associated to non-climatic drivers, but this dynamic might be strongly affected by the consequences of climate change and variability, with negative socio-economic impacts for the whole region.  相似文献