Magma mixing and convective compositional layering within the Vesuvius magma chamber   总被引：7，自引：0，他引：7  

Lucia Civetta  Rita Galati  Roberto Santacroce 《Bulletin of Volcanology》1991,53(4):287-300

The pumice-fall deposits of the last two Plinian eruptions of Vesuvius-a.d. 79 Pompei and 3700 b.p. Avellino-show a marked vertical compositional variation from white phonolite at the base to grey tephritic phonolite at the top. In both Avellino and Pompei sequences a compositional gap separates white from grey pumice. Grey and white pumice have distinct Sr and Nd isotopic compositions (grey pumice: ⁸⁷Sr/³⁶Sr=0.70749-56, ¹⁴³Nd/¹⁴⁴Nd=0.512507 for Pompei; 0.70760-69, 0.512504 for Avellino; white pumice: 0.70757-78 for Pompei; 0.70729-42 for Avellino). K-feldspar separated from both grey and white pumice has, in all cases, a white ⁸⁷Sr/⁸⁶Sr ratio (0.70766-79 for Pompei, 0.70728-33 for Avellino). The observed variations are interpreted as reflecting a pre-eruptive zonation of the magma chamber. Although mineralogical evidence of interaction between magma and calcareous country rocks exists in both eruptions, crustal contamination has not significantly modified the isotopic signatures of the erupted products. Petrographic and isotopic evidence of syneruptive magma mingling occur in Pompei grey pumice as well as in Avellino white and grey pumice, but they do not fully explain all the observed geochemical and isotopic variations. These variations are related to the complex refilling history of the magmatic system and result by fractional crystallization and mixing processes acting within the magma chamber. Preliminary data from other Plinian and subplinian sruptions of the Somma-Vesuvius point out the repeticive behaviour of ⁸⁷Sr/⁸⁶Sr variation in the last 25 000 years, hence suggesting a single magma chamber and continuity of the feeding system.  相似文献   

Seasonal DOC accumulation in the Black Sea: a regional explanation for a general mechanism   总被引：2，自引：0，他引：2  

Gustave Cauwet  Gaëlle Dliat  Anton Krastev  Galina Shtereva  Sylvie Becquevort  Christiane Lancelot  Andr Momzikoff  Alain Saliot  Adriana Cociasu  Lucia Popa 《Marine Chemistry》2002,79(3-4)

During three cruises in the Black Sea, organised in July 1995 and April–May 1997, biological and chemical parameters that can influence the carbon budget were measured in the water column on the NW shelf, particularly in the mixing zone with Danube River waters. We observed in early spring (end of April–May) conditions an important input of freshwater organisms that enhanced the microbial activity in the low salinity range. High bacterial activity regenerates nitrogen in the form of nitrates, but is also responsible for an important consumption of ammonium and phosphate, leading to a high N/P ratio and a strong deficit in phosphorus. The consequence is a limitation of phytoplankton development but also a production of carbohydrates that accumulate all along the salinity gradient. These mechanisms are responsible for a seasonal accumulation of dissolved organic carbon (DOC) that increases from 210 μM in winter to about 280 μM in summer. All this excess DOC disappears during winter, probably degraded by bacterial activity. The degradation of carbon-rich organic matter increases the phosphorus demand by bacteria bringing limitation to phytoplankton primary production.  相似文献   

Spatio-Temporal Distribution of Algal and Animal Communities in a Posidonia oceanica Meadow     

Lucia MaZzella  Maria Beatrice Scipione  Maria Cristina Buia 《Marine Ecology》1989,10(2):107-129

Abstract. Investigations were carried out in a Posidonia oceanica meadow at Ischia (Gulf of Naples) along a depth gradient from 1 to 32 m in November 1979 and May 1981.
In these two months, different discontinuities were found at the sampling stations (1, 5, 10, 20, 30 m) at 10 m for leaf features, between 1 and 5 m for the algal community and the vagile fauna. The leaf features (length, surface, and biomass) along the transects show a delay in leaf production toward the deeper stations, below the thermocline.
The algal community shows in both seasons and in all stations a persistence of an encrusting layer, mostly represented by Corallinaceae and the brown alga Myrionema orbiculare , while at the shallowest station (1 m) the community is characterized by a more developed upright layer.
The vagile fauna of the leaf stratum, mostly represented by Polychaeta, Mollusca , and Crustacea (Peracarida and Decapoda) , shows a consistent zonation in both seasons along the transect. A superficial community at I m, characterized by a low number of species and individuals and specialized for high environmental energy levels, and a deeper community, persistent in time and more strictly related to the Posidonia oceanica meadows, are identified.
The influence of environmental factors and the importance of meadow structure for the zonation of the algal and animal communities are discussed.  相似文献   

DNA and fluorescein tracer tests to study the recharge,groundwater flowpath and hydraulic contact of aquifers in the Umbria-Marche limestone ridge (central Apennines,Italy)     

Lucia Aquilanti  Francesca Clementi  Torquato Nanni  Stefano Palpacelli  Alberto Tazioli  Paola Maria Vivalda 《Environmental Earth Sciences》2016,75(7):626

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Occurrence and distribution of selected potentially toxic elements in soils of playing sites: a case study from Bratislava,the capital of Slovakia     

Edgar Hiller  Lucia Lachká  Ľubomír Jurkovič  Ondrej Ďurža  Katarína Fajčíková  Jaroslav Vozár 《Environmental Earth Sciences》2016,75(20):1390

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Performance of a base isolator with shape memory alloy bars   总被引：1，自引：1，他引：1  

Fabio Casciati  Lucia Faravelli  Karim Hamdaoui 《地震工程与工程振动(英文版)》2007,6(4):401-408

A new and innovative base isolation device is introduced in this paper based on extensive research carried out by the authors and their co-workers. A prototype of the device was built and experimentally tested on the shaking table. The new base isolation device consists of two disks, one vertical cylinder with an upper enlargement sustained by three horizontal cantilevers, and at least three inclined shape memory alloy (SMA) bars. The role of the SMA bars is to limit the relative motion between the base and the superstructure, to dissipate energy by their super-elastic constitutive law and to guarantee the re-centring of the device. To verify the expected performance, a prototype was built and tested under sinusoidal waves of displacement of increasing frequency with different amplitudes. It is shown that the main feature of the proposed base isolation device is that for cyclic loading, the super-elastic behavior of the alloy results in wide load-displacement loops, where a large amount of energy is dissipated.  相似文献   

Two Brazilian archaeological sites investigated by GPR: Serrano and Morro Grande     

Glria da Silva Cezar  Paula Lucia Ferrucio da Rocha  Angela Buarque  Ariovaldo da Costa 《Journal of Applied Geophysics》2001,47(3-4)

The application of the ground penetrating radar (GPR) at two archaeological sites, Serrano and Morro Grande, situated in Araruama County, Rio de Janeiro, Brazil, aids the study of a prehistoric indigenous culture, associated with the “Tupinambá” that inhabited the region during prehistoric times.The archaeological remains of the study area are mainly characterized by pottery artifacts for several uses, including funerary urns, which were buried within layers of sand and clay. Several profiles were acquired using a RAMAC system, with a 200 and 400 MHz frequency antennae. At the Serrano site, the profiles were acquired around some partially exposed pottery shards, due to sand exploitation. The resultant profiles provided a response model to guide the interpretation of new profiles acquired at other sites in the area, which present similar characteristics.The results showed the great importance of the dielectric permittivity contrast which exists between the targets and the host media, in order for possibly significant features to be identified in radar data.  相似文献   

Significance of orthopyroxene and major element constraints on the petrogenesis of Ferrar tholeiites from southern Prince Albert Mountains, Victoria Land, Antarctica     

G. Demarchi  P. Antonini  E. Piccirillo  G. Orsi  L. Civetta  M. D'Antonio 《Contributions to Mineralogy and Petrology》2001,142(2):127-146

The least evolved Jurassic Ferrar tholeiites from southern Prince Albert Mountains (Antarctica) are characterized by the occurrence of orthopyroxene (opx), a mineralogical feature virtually absent in the tholeiites from the large igneous provinces of Karoo (South Africa) and Paraná (Brazil). Petrography suggests that opx is the early phase in the sequence of crystallization and mineral chemistry indicates that it is in equilibrium with the host rock. In general, MELTS modeling predicts that opx is the liquidus phase in the Ferrar tholeiites with MgO higher than ~7 wt% at P=1.5-5 kbar, H₂O=0-1 wt% and % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaaiaacaqabeaabaqaamaaaOqaaiabdAga % MTWaaSbaaeaacqqGpbWtaeqaaWWaaSbaaeaadaWgaaqaaiabikdaYa % qabaaabeaakiabg2da9iabbgfarjabbAeagjabb2eanjabgkHiTiab % igdaXiaaysW7cyGGSbaBcqGGVbWBcqGGNbWzaaa!381A! = QFM - 1 f_{\rm O} _{_2 } = {\rm QFM} - 1\;\log unit conditions. MELTS results also show that the early crystallization of opx is primarily controlled by high SiO₂ and high SiO₂/CaO, chemical characteristics typical of the Ferrar tholeiites, but not shown by the Karoo and Paraná analogs with similar MgO content. Major element geochemistry of the least evolved Ferrar tholeiite has been modeled through fractional crystallization and fractional crystallization coupled with crustal assimilation processes, starting from natural peridotite-derived experimental melts. Mass balance and MELTS modeling support the argument that theoretical magma compositions suitable to be primary to the least evolved Ferrar tholeiites are compatible with hydrous (H₂O=0.3-0.5 wt%) and anhydrous melts obtained at 10-15 kbar by high melting degrees (>25%) of fertile and depleted spinel lherzolites, respectively, and later contaminated by the high-grade metamorphic rocks from the Victoria Land crystalline basement. The genesis of primary Ferrar tholeiites does not necessarily reflect the generally assumed depleted source mantle being also compatible with a fertile one.  相似文献   

Book reviews     

Mark S. T. Bukowinski  Philip E. Wannamaker  Manfred Koch  Yukio Fujinawa  Dr. Pradeep Talwani  D. Möhlmann  Andrew H. Knoll  Lucia Lovison-Golob  Krzysztof Haman  Hanna Pawłowska  Henryk Piwkowski  Dr. Anthony Dore  Nguyen Xuan Huy  Edward R. Cook  Jan Błecki  Jacek Leliwa-Kopystynski  Magdalena Sroczynska-Kozuchowska 《Pure and Applied Geophysics》1993,140(1):139-177

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Mantle source heterogeneity in the Campanian Region (South Italy) as inferred from geochemical and isotopic features of mafic volcanic rocks with shoshonitic affinity   总被引：6，自引：0，他引：6  

M. D'Antonio  L. Civetta  P. Di Girolamo 《Mineralogy and Petrology》1999,67(3-4):163-192

Summary Major, trace element and Sr-Nd-isotopic data on mafic volcanic rocks with shoshonitic affinity from the islands of Procida and Ventotene (Campanian Region, South Italy) are reported. Within-suite chemical and isotopic variations are interpreted in terms of open system differentiation processes held responsible for enrichment in a number of trace elements and for radiogenic Sr observed in both Procida and Ventotene volcanic sequences. Conversely, trace element contents and Sr-Nd-isotopic compositions of the least-evolved among the investigated samples are thought to reflect source region characteristics with only negligible crustal contamination of the primary magmas.The data support an origin from distinct source regions for the primary magmas. In the case of Ventotene, the source would have been asthenospheric and/or lithospheric mantle with features similar to transitional mid-ocean ridge basalts (T-MORB), modified by enriching agents made up mainly of subducted slab-released components coming from marly sediments (about 7%) similar to cherts from Tuscan Apennines plus a limestone contribution. In the case of Procida, the source would have been asthenospheric and/or lithospheric mantle with a slightly more enriched T-MORB-like feature with respect to Ventotene, modified by slab-derived enriching agents, likely represented by a small amount of sediments (about 2.5%) of oceanic nature (mostly terrigenous/pelagic). These differences are constrained by lower Zr/Nb, Y/Nb, Sc/Nb, V/Nb, LILE/HFSE, LREE/HFSE and⁸⁷Sr/⁸⁶Sr, higher Ba/La and¹⁴³Nd/¹⁴⁴Nd ratios, as well as by the lack of a detectable negative Eu anomaly, in the least-evolved volcanic rocks of Procida, with respect to those of Ventotene, which show conversely a significant negative Eu anomaly. Thus, a sharp heterogeneity exists in the mantle beneath the Campanian Region. It is thought to be the consequence of two different slabs which are in contact along the Volturno River Plain tectonic line: a continental slab, seismically inactive, descending beneath the Latium Region, and an oceanic slab, seismically active, descending beneath the Calabria, up to the Campanian Region.

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Résumé De nouvelles analyses géochimiques d'éléments majeurs et en traces ainsi que des rapports isotopiques du Sr et du Nd sont été obtenues sur des roches volcaniques mafiques à affinité shoshonitiques provenant des îles de Procida et Ventotene (Région Campanienne, Italie du Sud). Les variations géochimiques et isotopiques observées au sein des séries volcaniques de ces deux îles sont interprétées en terme de processus de différenciation en système ouvert, tenu pour responsable d'un enrichissement d'un certain nombre d'éléments en traces et de leur composition en Sr radiogénique. Cependant, les teneurs en éléments traces et les compositions isotopiques en Sr et Nd des échantillons les moins évolués parmi ceux étudiés reflètent les caractéristiques de leur source, avec une contamination crustale très négligeable des magmas primitifs.Ces données démontrent que des sources distinctes sont à l'origine des magmas primitifs. Pour Ventotene, cette source doit être un manteau asthénosphérique et/ou lithosphérique dont la signature est similaire à celle de basaltes transitionnels de dorsale océanique (T MORB), légèrement enrichie en éléments dérivants d'une croûte plongeant dans une subduction comme des sédiments mameux (pour environ 7%) analogues aux cherts des Appenins de Toscane et comportant un apport en calcaire. Dans le cas de Procida, cette source doit être un manteau asthénosphérique et/ou lithosphérique montrant une signature de type T-MORB légèrement plus enrichie qu' à Ventotene, également modifiée par un apport venant d'une croûte en subduction, probablement une faible quantité (environ 2.5%) de sédiments de nature océanique (principalement terrigène/pélagique). Ces différences sont attestées par des rapports Zr/Nb, Y/Nb, Sc/Nb, V/Nb, LILE/HFSE, LREE/HSFE and⁸⁷Sr/⁸⁶Sr plus bas et des rapports Ba/La et¹⁴³Nd/¹⁴⁴Nd plus harts, ainsi que par l'absence d'une anomalie en Eu dans les compositions des roches volcaniques les moins évoluées de Procida par rapport à celles de Ventotene, qui elles, au contraire, montrent une anomalie en Eu significative.Ainsi, une importante hétérogénéité du manteau existe sous la Campanie. Cette hétérogénéité doit être la conséquence de la nature différente des croûtes en subduction et qui sont en contact le long de la ligne tectonique de la plaine de la rivière Volturno: an Nord-Ouest, une croûte continentale, sismiquement inactive, plonge sous le Latium alors qu'au Sud-Est, une croûte océanique, sismiquement active, plonge sous la Calabre et jusque sous la Campanie.

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With 9 Figures  相似文献