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1.
Summary Volcanic rocks on Ponza Island (Tyrrhenian Sea, central Italy) consist of Pliocene submarine rhyolites and Pleistocene subaerial
trachyte and comendite lavas. Chemical variations and the homogeneous Sr and Nd isotopic signatures within the analyzed Pliocene
rocks are ascribed to crystal fractionation. The absolute isotopic values, however, indicate the important role of a crustal
component in the origin of these magmas. The very high-silica rocks were probably derived from a superimposed mechanism which
may have been connected to the ascent of hydrothermal magmatic fluids.
Compositional and 87Sr/86Sr variations at constant 143Nd/144Nd values in the Pleistocene rocks are likely due to fractionation of the observed phenocryst assemblage, possibly coupled
with minor crustal interaction. These processes, however, cannot account for the extreme enrichment of many incompatible trace
elements in the comendites. Some evidence suggests the influence of a halogen- and/or CO2-rich volatile phase.
Received February 17, 2000; revised version accepted November 29, 2000 相似文献
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Carlos M. Alonso-Hernández Fabio Conte Cristina Misic Mattia Barsanti Miguel Gómez-Batista Misael Díaz-Asencio Anabella Covazzi-Harriague Federica G. Pannacciulli 《Continental Shelf Research》2011,31(7-8):749-757
The main environmental features of the Gulf of Batabanó, Cuba, Caribbean, were investigated through the analyses of surface sediments collected at 23 sites. In order to highlight the potential threats affecting the sedimentary compartment of this area, samples were analysed for: granulometry, mineralogy, heavy metals concentration (As, Cd, Cu, Mn, Ni, Pb, Zn), organic carbon, total nitrogen and radionuclides. Findings were compared with published data and “grey” literature.Results showed: granulometric homogeneity and a widespread carbonatic condition all over the gulf, probably due to stable bathymetry and lack of terrigenous input (except for the La Coloma basin); a rather pristine environment for what concerns heavy metals pollution, except for La Coloma where a large arsenic input was recorded; very low levels of natural and artificial radioactivity; a relevant quantity of sedimentary organic matter, providing biota with useful substrate for feeding and enhancing the food-web development while indirectly supplying lobster fisheries. Combined data highlighted the impact of the Dique Sur in reducing terrigenous input in the coastal area.Future studies should focus on dating of sediment cores for identifying and quantifying the changes acting in the gulf and on investigating the origins of the large arsenic input to La Coloma. 相似文献
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P. van Beek R. François M. Conte J.-L. Reyss M. Charette 《Geochimica et cosmochimica acta》2007,71(1):71-86
We measured 228Raex/226Raex and 226Raex/Baex ratios in suspended and sinking particles collected at the Oceanic Flux Program (OFP) time-series site in the western Sargasso Sea and compared them to seawater ratios to provide information on the origin and transport of barite (BaSO4) in the water column. The 228Raex/226Raex ratios of the suspended particles down to 2000 m are nearly identical to those of seawater at the same water depth. These ratios are much lower than expected if suspended barite was produced in surface waters and indicate that barite is produced throughout the mesopelagic layer. The 228Raex/226Raex activity ratios of sinking particles collected at 1500 and 3200 m varied mostly between 0.1 and 0.2, which is intermediate between the seawater ratio at these depths (<0.03) and the seawater ratios found in the upper 250 m (0.31-0.42). This suggests that excess Ba (i.e., Baex = Batotal − Balithogenic), considered to be mainly barite, present in the sinking flux is a mixture of crystals formed recently in the upper water column, formed several years earlier in the upper water column, or formed recently in deeper waters. We observe a sizeable temporal variability in the 228Raex/226Raex ratios of sinking particles, which indicates temporal variability in the relative proportion of barite crystals originating from surface (with a high 228Raex/226Raex ratio) and mesopelagic (with a low 228Raex/226Raex ratio) sources. However, we could not discern a clear pattern that would elucidate the factors that control this variability. The 226Ra/Ba ratios measured in seawater are consistent with the value reported from the GEOSECS expeditions (2.3 dpm μmol−1) below 500 m depth, but are significantly lower in the upper 500 m. High 226Raex/Baex ratios and elevated Sr concentrations in suspended particles from the upper water column suggest preferential uptake of 226Ra over Ba during formation of SrSO4 skeletons by acantharians, which must contribute to barite formation in shallow waters. Deeper in the water column the 226Raex/Baex ratios of suspended particles are lower than those of seawater. Since 228Raex/226Raex ratios demonstrate that suspended barite at these depths has been produced recently and in situ, their low 226Raex/Baex ratios indicate preferential uptake of Ba over Ra in barite formed in mesopelagic water. 相似文献
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In the present paper, a finite element approach is proposed to analyse the mobility of active landslides which are controlled by groundwater fluctuations within the slope. These landslides are usually characterised by low displacement rates with deformations that are essentially concentrated within a narrow shear zone above which the unstable soil mass moves with deformations of no great concern. The proposed approach utilises an elasto-viscoplastic constitutive model in conjunction with a Mohr-Coulomb yield function to describe the behaviour of the soil in the shear zone. For the other soils involved by the landslide, an elastic model is used for the sake of simplicity. A significant advantage of the present method lies in the fact that few constitutive parameters are required as input data, the most of which can be readily obtained by conventional geotechnical tests. The rest of the required parameters should be calibrated on the basis of the available monitoring data concerning the change in the piezometric levels and the associated movements of the unstable soil mass. After being calibrated and validated, the proposed approach can be used to predict future landslide movements owing to expected groundwater fluctuations or to assess the effectiveness of drainage systems which are designed to control the landslide mobility. The method is applied to back-predict the observed field behaviour of three active slow-moving landslides documented in the literature. 相似文献
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Peer Helmke Susanne Neuer Michael W. Lomas Maureen Conte Tim Freudenthal 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(2):213-227
We compared in-situ and satellite-derived measures of the biological carbon pump efficiency at the two seemingly similar subtropical North Atlantic gyre time series sites, the Bermuda time series (BATS, Bermuda Atlantic time-series study and OFP, ocean flux program) in the western gyre and the ESTOC time series (European station for time-series in the ocean, Canary Islands) in the eastern gyre. Satellite-derived surface chlorophyll a was slightly lower at Bermuda compared to ESTOC (annual average of 0.10±0.04 vs. 0.14±0.05-mg-m?3), as was satellite-derived primary production (annual average of 380±77 vs. 440±80-mg C-m?2 d?1). However, export production normalized to primary production (export ratio) was higher at Bermuda by a factor of 2–3 when estimated using mesopelagic traps moored at 500-m depth and by a factor of 3–4 when estimated using surface-tethered drifting traps. When averaged seasonally, flux at BATS was highest in spring (March, April, May) at all depths followed by summer (June, July, August) and decreasing towards fall, but this seasonality was less visible at ESTOC. Seasonal comparison showed the fastest flux attenuation at Bermuda in winter and spring, coinciding with the highest POC flux. POC/PIC ratios derived from the moored traps were significantly higher at BATS than at ESTOC in fall and winter, but this difference was not significant in spring (p>0.05). This study shows that while the western and eastern Atlantic subtropical gyres have similar rates of primary production, the biological carbon pump differs between the two provinces. Higher new nutrient input observed at Bermuda compared to ESTOC might explain part of the difference in export ratio but alone is insufficient. Greater winter mixed-layer depths and higher mesoscale eddy activity at Bermuda resulting in pulsed production events of labile organic matter might explain both the higher export flux and export ratios found at Bermuda. 相似文献
6.
Seismic vulnerability of bridges in transport networks subjected to environmental deterioration 总被引：1，自引：1，他引：0
Mariano Angelo Zanini Carlo Pellegrino Riccardo Morbin Claudio Modena 《Bulletin of Earthquake Engineering》2013,11(2):561-579
This paper investigates the problem of management, maintenance and planning of interventions in transport networks located in seismic zones, in relation to the actual state of degradation of their most vulnerable elements, as bridges. The study consists in two phases: the first phase is concerned with definition of the seismic vulnerability of a typical bridge in the network, through the construction of fragility curves calculated taking into account the corrosion of the reinforcing steel as the main cause of environmental deterioration. Once the fragility curves of the deteriorated bridges are computed, the second phase consists in the analysis of the vulnerability of the transport network in which the bridges are included taking into account the modification of the traffic flows when bridge infrastructures are damaged. The results of this pilot study can be used as a first step for a proper allocation of economic resources in the planning of seismic retrofit interventions to minimize the overall risk and manage the immediate post-earthquake emergency phase and guide rescuers in reaching the affected and critical areas. 相似文献
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Seismic stability analysis of reinforced slopes 总被引：4，自引：0，他引：4
In this paper, the seismic stability of slopes reinforced with geosynthetics is analysed within the framework of the pseudo-static approach. Calculations are conducted by applying the kinematic theorem of limit analysis. Different failure modes are considered, and for each analytical expressions are derived that enable one to readily calculate the reinforcement force required to prevent failure and the yield acceleration of slopes subjected to earthquake loading. Several results are presented in order to illustrate the influence of seismic forces on slope stability. Moreover, a suitable procedure based on the assessment of earthquake-induced permanent displacement is proposed for the design of reinforced slopes in seismically active areas. 相似文献
10.
Nonlinear FE model updating and reconstruction of the response of an instrumented seismic isolated bridge to the 2010 Maule Chile earthquake 
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下载免费PDF全文 Nonlinear finite element (FE) modeling has been widely used to investigate the effects of seismic isolation on the response of bridges to earthquakes. However, most FE models of seismic isolated bridges (SIB) have used seismic isolator models calibrated from component test data, while the prediction accuracy of nonlinear FE models of SIB is rarely addressed by using data recorded from instrumented bridges. In this paper, the accuracy of a state‐of‐the‐art FE model is studied through nonlinear FE model updating (FEMU) of an existing instrumented SIB, the Marga‐Marga Bridge located in Viña del Mar, Chile. The seismic isolator models are updated in 2 phases: component‐wise and system‐wise FEMU. The isolator model parameters obtained from 23 isolator component tests show large scatter, and poor goodness of fit of the FE‐predicted bridge response to the 2010 Mw 8.8 Maule, Chile Earthquake is obtained when most of those parameter sets are used for the isolator elements of the bridge model. In contrast, good agreement is obtained between the FE‐predicted and measured bridge response when the isolator model parameters are calibrated using the bridge response data recorded during the mega‐earthquake. Nonlinear FEMU is conducted by solving single‐ and multiobjective optimization problems using high‐throughput cloud computing. The updated FE model is then used to reconstruct response quantities not recorded during the earthquake, gaining more insight into the effects of seismic isolation on the response of the bridge during the strong earthquake. 相似文献