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181.
Laboratory extraction experiments and field observations were employed to determine the relative mobility of 239,240pu and 241Am from lake sediments under aerobic and anaerobic conditions. Laboratory investigations show that under aerobic conditions 241Am is more readily extracted from Lake Michigan sediments than is 239,240Pu. Under anaerobic conditions, the extractability of plutonium and americium does not increase significantly relative to aerobic conditions. Field studies indicate that neither element is recycled from the sediment to the overlying water column during anaerobic conditions attendant with thermal stratification. The adsorption of these elements onto sediments does not appear to be correlated with extractable iron, manganese, and organic compounds such as humic and fulvic acids. 相似文献
182.
Avanzinelli Riccardo; Elliott Tim; Tommasini Simone; Conticelli Sandro 《Journal of Petrology》2008,49(2):195-223
We present new U-series isotope, 87Sr/ 86Sr, 143Nd/ 144Nd andtrace element data for a set of mafic, K-rich rocks from volcanoesin Central–Southern Italy. These shoshonitic to ultrapotassiclavas display strongly depleted high field strength element(HSFE) abundances with respect to other incompatible trace elementstogether with high but variable 87Sr/ 86Sr and low but variable143Nd/ 144Nd values. Such characteristics are thought to bedue to addition of subducted crust of variable amount and compositionto their mantle sources prior to magma genesis. Rocks from thenorthernmost region (i.e. Tuscan Magmatic Province and NorthernRoman Magmatic Province) display (230Th/ 238U) activity ratiosclose to radioactive equilibrium, suggesting that metasomatismof their sources occurred before 400 ka and recent melting tookplace at shallow depths, in the absence of garnet. A 238U excessof up to 27% has been measured in rocks from the NeapolitanDistrict. The occurrence of significant U excesses is a featureof arc magmas, but is typically seen in depleted lavas ratherthan in highly enriched rocks such as these (20 ppm Th). Thissignature requires a recent addition of a U-rich component tothe already strongly enriched mantle wedge beneath this regionof Italy. We suggest that a supercritical liquid, from deeplysubducted carbonate-rich sediments of the still-active Ionianslab, is responsible for generating a high-U, low-Th component,which produces the observed disequilibria. A 30% 230Th excessmeasured in a single unaltered sample from the Lucanian MagmaticProvince, along with a less marked negative HFSE anomaly, suggeststhe contribution of a deeper, garnet-bearing component in thegenesis of these magmas, plausibly related to the upwellingof asthenospheric mantle around the corner of the Ionian slab. KEY WORDS: U/Th disequilibria; potassic and ultrapotassic rocks; subduction: metasomatism; mantle melting; Central and Southern Italy 相似文献
183.
Carlos J.S. de Alvarenga Marcel A. Dardenne Roberto V. Santos Emanuele R. Brod Simone M.C.L. Gioia Alcides N. Sial Elton L. Dantas Valderez P. Ferreira 《Gondwana Research》2008,13(4):469-479
The Neoproterozoic carbonate sequence on the southeastern border of the Amazon Craton is divided into three lithostratigraphic units: a basal cap dolomite, an intermediate limestone, limestone-mudstone unit, and an upper dolarenite-dolorudite unit. Sections of the cap-carbonate were measured from the inner shelf to the outer shelf. Carbon isotope ratios (relative to PDB) vary between − 10.5 and − 1.7‰ in cap dolomite, and between − 5.4 and + 0.1‰ in laminated limestone and mud-limestone. Limestones and mud-limestones exhibit 87Sr/86Sr ratios ranging from 0.70740 to 0.70780. A comparative isotope stratigraphy between the inner-shelf and the middle-shelf basin shows differences in carbon isotope ratios: The cap dolomite and limestones have lower δ13C ratios on the border of the basin (inner shelf) than in the middle shelf of the basin. These lower values can be related to shallower environmental conditions and to a stronger influence of the continental border. The 87Sr/86Sr ratios are the same in both areas, and are consistent with seawater composition at around 600 Ma. 相似文献
184.
Michela Garau Maria Grazia Badas Simone Ferrari Alessandro Seoni Giorgio Querzoli 《Boundary-Layer Meteorology》2018,167(1):123-143
We experimentally investigate the effect of a typical building covering: the gable roof, on the flow and air exchange in urban canyons. In general, the morphology of the urban canopy is very varied and complex, depending on a large number of factors, such as building arrangement, or the morphology of the terrain. Therefore we focus on a simple, prototypal shape, the two-dimensional canyon, with the aim of elucidating some fundamental phenomena driving the street-canyon ventilation. Experiments are performed in a water channel, over an array of identical prismatic obstacles representing an idealized urban canopy. The aspect ratio, i.e. canyon-width to building-height ratio, ranges from 1 to 6. Gable roof buildings with 1:1 pitch are compared with flat roofed buildings. Velocity is measured using a particle-image-velocimetry technique with flow dynamics discussed in terms of mean flow and second- and third-order statistical moments of the velocity. The ventilation is interpreted by means of a simple well-mixed box model and the outflow rate and mean residence time are computed. Results show that gable roofs tend to delay the transition from the skimming-flow to the wake-interference regime and promote the development of a deeper and more turbulent roughness layer. The presence of a gable roof significantly increases the momentum flux, especially for high packing density. The air exchange is improved compared to the flat roof buildings, and the beneficial effect is more significant for narrow canyons. Accordingly, for unit aspect ratio gable roofs reduce the mean residence time by a factor of 0.37 compared to flat roofs, whereas the decrease is only by a factor of 0.9 at the largest aspect ratio. Data analysis indicates that, for flat roof buildings, the mean residence time increases by 30% when the aspect ratio is decreased from 6 to 2, whereas this parameter is only weakly dependent on aspect ratio in the case of gable roofs. 相似文献
185.
José A. M. Demattê Julianne de Castro Oliveira Tiago Rodrigues Tavares Leonardo Ramirez Lopez Fabrício da Silva Terra Suzana Romeiro Araújo Caio Troula Fongaro Stoécio Malta Ferreira Maia Francisco Fujita de Castro Mello Rodnei Rizzo Simone Vicente Marco Antonio de Melo Bortolleto Pedro Henrique Ramos Cerqueira 《Environmental Earth Sciences》2016,75(18):1277
186.
Tectonic activation,source area stratigraphy and provenance changes in a rift basin: the Early Cretaceous Tucano Basin (NE‐Brazil) 下载免费PDF全文
Felipe T. Figueiredo Renato P. Almeida Bernardo T. Freitas Andre Marconato Simone C. Carrera Bruno B. Turra 《Basin Research》2016,28(4):433-445
Changes in sandstone and conglomerate maturity in tectonically active basins can be considered either as the product of climatic change or of tectonic restructuring of the feeder drainage system. Besides these regional controls, changes in the configuration of local sources can expressively affect basin fill composition. The Early Cretaceous fluvial successions of the Tucano Basin, a rift basin in northeastern Brazil related to the South Atlantic opening, contain one such case of abrupt change in maturity, marked by the passage from pebbly sandstone and conglomerate rich in quartz and quartzite fragments (Neocomian to Barremian São Sebastião Formation) to more feldspathic pebbly sandstone and conglomerate bearing pebbles of varied composition (Aptian Marizal Formation). Systematic analysis of stratigraphic and spatial variation in palaeocurrents and composition of pebbles and cobbles from both units, integrated with the recognition of fluvial and alluvial fan deposits distribution, revealed an abrupt decrease in maturity during the passage from the São Sebastião Formation to the Marizal Formation. This change is explained by exhumation of basement rocks and erosional removal of originally widespread Silurian to Jurassic sandstone and conglomerate units which were a major source of reworked vein quartz and quartzite pebbles to the São Sebastião Formation. Basin border faults activation during the deposition of the Marizal Formation caused adjacent basement uplift above the local erosional base level at the basin borders, whereas during the São Sebastião Formation deposition, the basin border fault scarps probably exposed mineralogically mature sedimentary units. The proposed model has important implications for interpreting changes in sediment maturity in rift basin successions, as similar results are expected where activation of basin border faults occurs after the erosional removal of older sedimentary or volcanic units that controlled syn‐rift successions composition. 相似文献
187.
Fiorani Luca Santoro Simone Parracino Stefano Maio Giovanni Nuvoli Marcello Aiuppa Alessandro 《Natural Hazards》2016,83(1):21-29
Volcanic gases give information on magmatic processes. In particular, anomalous releases of carbon dioxide precede volcanic eruptions. Up to now, this gas has been measured in volcanic plumes with conventional measurements that imply the severe risks of local sampling and can last many hours. For these reasons and for the great advantages of laser sensing, the thorough development of volcanic lidars has been undertaken at ENEA (Italian National Agency for New Technologies, Energy and Sustainable Economic Development). In fact, lidar profiling allows one to scan remotely volcanic plumes in a fast and continuous way, and with high spatial and temporal resolution. A differential absorption lidar instrument will be presented in this paper: BILLI (BrIdge voLcanic LIdar). It is based on injection-seeded Nd:YAG laser, double-grating dye laser, difference frequency mixing and optical parametric amplifier. BILLI is funded by the ERC (European Research Council) project BRIDGE (BRIDging the gap between Gas Emissions and geophysical observations at active volcanos). It scanned the gas emitted by Pozzuoli Solfatara (Naples, Italy) and Stromboli Volcano (Sicily, Italy) during field campaigns carried out from October 13 to 17, 2014, and from June 24 to 29, 2015, respectively. Carbon dioxide concentration maps were retrieved remotely in few minutes in the crater areas. To our knowledge, it is the first time that carbon dioxide in a volcanic plume is retrieved by lidar. This result represents the first direct measurement of this kind ever performed on active volcanos and shows the high potential of laser remote sensing in early detection of volcanic hazard. 相似文献
188.
Simone Scapin Francesco Apadula Michele Brunetti Maurizio Maugeri 《Theoretical and Applied Climatology》2016,125(3-4):729-742
189.
Tommasini Simone; Heumann Arnd; Avanzinelli Riccardo; Francalanci Lorella 《Journal of Petrology》2007,48(12):2407-2430
The subaerial part of the Stromboli stratovolcano was builtup in the last 100 kyr through six periods of activity; theerupted magmas record the largest compositional variation ofall the Aeolian arc volcanoes (calc-alkaline, shoshonitic, andpotassic alkaline magma series). The trace element characteristicsof the less evolved magmas of each period of activity are coherentlycorrelated with their radiogenic isotope (Sr, Nd, Pb) composition,and are typical of volcanic arc rocks. In terms of U-seriesisotopes, samples from the different magma series have both238U and 230Th excesses, and this distinctive feature providesadditional constraints on source enrichment processes withinthe mantle wedge and on the mechanism of partial melting. Overallthe complete set of data demonstrates that the genesis of thedifferent magma series at Stromboli can be accommodated in amantle source that experienced two distinct enrichment processesby different parts of the subducting oceanic crust of the Ionianslab. The first was caused by supercritical liquids originatingfrom the basaltic and sedimentary parts of the subducting slabat >5 GPa and 900°C. The second was induced by aqueousfluids, again originating from the basaltic and sedimentaryparts of the slab, released from a shallower part of the subductedIonian slab (< 5 GPa and 800°C). U–Th disequilibriaconstrain the timing of the first metasomatic event (Stage I:supercritical liquids) at >435 ka, whereas the second event(Stage II: aqueous fluids) occurred at 100 ka. The high-angledip of the Ionian slab (70°) caused the superimpositionof the metasomatizing agents of the two enrichment processesin the same volume of the mantle wedge, explaining the occurrenceof such different magma series in a single volcanic edifice.The U–Th disequilibria provide evidence for dynamic meltingof the metasomatized mantle wedge combined with an ageing effectresulting from the restoration of secular equilibrium afterthe perturbation caused by the U-rich aqueous fluids of StageII. The trace element and radiogenic isotope (U, Th, Sr, Nd,Pb) signature of the mantle source of the magmas at Stromboliis thus dependent upon the amount of supercritical liquids andaqueous fluids released by the two components of the subductedslab, whereas the distinctive 238U and 230Th excesses of themagmas result from a combination of mantle ageing and time-dependentdynamic melting. The geochemical and radiogenic isotope signatureof the mantle source beneath Stromboli places important constraintson the isotopic polarity from Southern Latium to the Aeolianarc attributed to the effect of a HIMU mantle component followingeither lateral inflow of foreland mantle material or upwellingof a mantle plume in the centre of the Tyrrhenian basin. Ourgeochemical model demonstrates that the high 206Pb/204Pb ofthe putative HIMU mantle component could be equallyformed during metasomatism of the pre-existing mantle wedgeby either the supercritical liquid (Stage I) or aqueous fluid(Stage II) released by the subducted altered basalt of the Ionianplate. KEY WORDS: radiogenic isotopes; U–Th disequilibria; mantle metasomatism; supercritical liquid; aqueous fluid; Stromboli 相似文献
190.