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排序方式: 共有260条查询结果,搜索用时 31 毫秒
191.
Simone Scapin Francesco Apadula Michele Brunetti Maurizio Maugeri 《Theoretical and Applied Climatology》2016,125(3-4):729-742
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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
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196.
AbdouMaliq Simone 《Singapore journal of tropical geography》2008,29(2):186-204
Phnom Penh, 're-entering' urban history as it did just some three decades ago becomes an important arena in which to focus on the intensifying contestation of rights, practices and development trajectories related to city making. Far from being comprehensively marginalized by emerging urban economies, residents with limited economic means, through their configurations of space, social relations and infrastructure continuously attempt to construct the conditions that enable the city to act as a flexible resource for the viable organization of their everyday lives. These issues are taken up in an analysis of some of the ways in which residents of a large low income housing tract, popularly dubbed 'Building', in the Bassac River neighbourhood collaborate to maximize their access to resources and opportunity. 相似文献
197.
Isolation and characterization of crude-oil-degrading bacteria from the Persian Gulf and the Caspian Sea 总被引:2,自引:0,他引:2
Twenty-five crude-oil-degrading bacteria were isolated from oil-contaminated sites in the Persian Gulf and the Caspian Sea. Based on a high growth rate on crude oil and on hydrocarbon degradation ability, 11 strains were selected from the 25 isolated strains for further study. Determination of the nucleotide sequence of the 16S rRNA gene showed that these isolated strains belonged to genera Acinetobacter, Pseudomonas, Gordonia, Rhodococcus, Cobetia, Halomonas, Alcanivorax, Marinobacter and Microbacterium. Among the 11 isolates, strains BS (Acinetobacter calcoaceticus, 98%) and PG-12 (Alcanivorax dieselolei, 98%) were the most effective in degrading crude oil. Rate of crude-oil degradation of 82% (isolate BS) and 71% (isolate PG-12) were observed after 1 week of cultivation in mineral medium. These strains had high emulsification activity and biosurfactant production. GC-MS analysis showed that A. dieselolei PG-12 can degrade different alkanes in crude oil. Screening of the distribution of the alkane hydroxylase gene in 25 isolates in relation to the source of isolation indicated that the group (II) alkane hydroxylase is prevalent in the Caspian Sea, but in the Persian Gulf, the frequency of the group (III) alkane hydroxylase gene is greater than that of the group (II) alkane hydroxylase gene. 相似文献
198.
Simone Castiglioni Laura Lombardi Elena Toth Attilio Castellarin Alberto Montanari 《Advances in water resources》2010
Parameter estimation for rainfall-runoff models in ungauged basins is a challenging task that is receiving significant attention by the scientific community. In fact, many practical applications suffer from problems induced by data scarcity, given that hydrological observations are often sparse or unavailable. This study focuses on regional calibration for a generic rainfall-runoff model. The maximum likelihood function in the spectral domain proposed by Whittle [40] is approximated in the time domain by maximising the fit of selected statistics of the river flow process, with the aim to propose a calibration procedure that can be applied at regional scale. Accordingly, the statistics above are related to the dominant climate and catchment characteristics, through regional regression relationships. The proposed technique is applied to the case study of 4 catchments located in central Italy, which are treated as ungauged and are located in a region where detailed hydrological, as well as geomorphologic and climatic information, is available. The results obtained with the regional calibration are compared with those provided by a classical least squares calibration in the time domain. The outcomes of the analysis confirm the potential of the proposed methodology and show that regional information can be very effective for setting up hydrological models. 相似文献
199.
Paolo Augliera Ezio D’Alema Simone Marzorati Marco Massa 《Bulletin of Earthquake Engineering》2010,8(5):1091-1104
The necessity of a dense network in Northern Italy started from the lack of available data after the occurrence of the 24th
November 2004, Ml 5.2, Salò earthquake. Since 2006, many efforts have been made by the INGV (Italian National Institute for Geophysic and Vulcanology), Department of Milano-Pavia (hereinafter INGV MI-PV), to improve the strong-motion monitoring of the Northern Italy regions.
This activity led to the installation of a strong-motion network composed by 20 accelerometers, 4 coupled with 20-bits Lennartz
Mars88 recorders, 12 coupled with 24-bits Reftek 130 recorders and 4 coupled with 24-bits Gaia2 recorders. The network allow
us to reduce, in the area under study, the average inter-distances between strong-motion stations from about 40 km (at November
2004) to 15 km. At present the network includes nine 6-channels stations where velocity sensors work together the strong-motion
ones. The data transmission is assured by modem-gsm, with the exception of four stations that send data in real time through
a TCP/IP protocol. In order to evaluate different site responses, the stations have been installed both in free field and
near (or inside) public buildings, located in the center of small villages. From June 2006 to December 2008 a dataset of 94
events with local magnitude range from 0.7 to 5.1 has been collected. An ad hoc data-processing system have been created in
order to provide, after each recorded event, engineering parameters such as peak ground acceleration (PGA) and velocity (PGV),
response spectra (SA and PSV), Arias and Housner intensities. Data dissemination is achieved through the web site , while the waveforms are distributed through the Italian strong motion database (). 相似文献
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