K-Rb ratio in high grade metamorphism: A confirmation of the hypothesis of a continual crustal evolution     

G. Paolo Sighinolfi 《Contributions to Mineralogy and Petrology》1969,21(4):346-356

The K:Rb ratio (R) in a metamorphic sequence with increasing metamorphism of the West Alps has been analysed. By a regression analysis a comparison is made with the trends observed for R byShaw (1968) in many magmatic processes. The K:Rb ratio in the metamorphic rocks shows a marked increase with increasing metamorphism in relation to a removal of the K content. The arithmetic averages of R in the rocks of amphibolite and granulite facies are 231 and 505 respectively. In some samples of granulite facies the R values are higher than those of the continental alkalic basalts and approximate to the oceanic tholeiites. The variations in the K:Rb ratio may be imputed, according toShaw, to an anatexis process which took place under high grade metamorphic conditions. The marked increase of the K:Rb ratio in the deep material would be caused by partial separation between K and Rb in the granulite assemblages and by an upward migration of Rb, relative to K, from the deep crustal levels of granulite facies. These considerations seem to confirmShaw’s hypothesis of the possibility of a marked crustal stratification and consequently of a continual crustal evolution.  相似文献   

Magma contamination by direct wall rock interaction: constraints from xenoliths from the walls of a carbonate-hosted magma chamber (Vesuvius 1944 eruption)     

Aldo Del Moro  Paolo Fulignati  Paola Marianelli  Alessandro Sbrana   《Journal of Volcanology and Geothermal Research》2001,112(1-4)

During the 1944 eruption of Vesuvius different types of xenoliths were ejected. They represent fragments of the walls of a low volume (<0.5 km³) shallow (3–4 km depth) magma chamber. The study of these xenoliths enables us to estimate the amount of contamination occurring at the boundary of a high-T alkaline magma chamber hosted in carbonate rocks. The process of contamination of the magma by carbonates can be modelled, using isotopic and chemical data, as a mixing between magma and marbles. Mass exchanges occur at the boundary between the crystallizing magma and marble wall rocks, where endoskarn forms. The contamination of the solidification front of the chamber is very limited. The solidification front and the skarn shell effectively isolate the interior of the magma chamber from new inputs of contaminants from the carbonate wall rocks. Therefore, the main volume of magma, hosted in the magma chamber, did not undergo any significant mass exchange with the wall rocks.  相似文献   

Insights into present-day crustal motion in the central Mediterranean area from GPS surveys   总被引：3，自引：0，他引：3  

Marco Anzidei  Paolo Baldi  Giuseppe Casula  Alessandro Galvani  Enzo Mantovani  Arianna Pesci  Federica Riguzzi  Enrico Serpelloni 《Geophysical Journal International》2001,146(1):98-110

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Precise, absolute earthquake location under Somma–Vesuvius volcano using a new three-dimensional velocity model     

Anthony Lomax  Aldo Zollo  Paolo Capuano  Jean Virieux 《Geophysical Journal International》2001,146(2):313-331

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Recent sea-level changes and related engineering problems in the Lagoon of Venice (Italy)     

Paolo Antonio Pirazzoli 《Progress in Oceanography》1987,18(1-4)

In the city of Venice, where the average altitude is only a few tens of centimetres, there has been a dangerous increase in the frequency of flooding during the past few decades.Since 1872, the average increase in flooding levels (“acqua alta”) has been about 40cm: 27cm of this is due to the local rise in mean sea-level (of which some 14cm are related to man-induced subsidence of land, and 3–7cm to geological factors), and at least 14cm are caused by hydrodynamical factors, of which about 10cm can be ascribed to man-induced tidal changes. These latter are due above all to the dredging of deep artificial channels, the reclamation of wide areas of tidal flats, and the diking of fish ponds (“valli”), which have changed the ratio between the surface of the lagoon and that of the inlets. Since the latest modification (1963–1969), the lagoon has been open to large oil tankers, thereby allowing an easier entry of storm surges arising out at sea.Indeed an incompatibility exists between the accessibility of very large boats to the lagoon and the safeguard of Venice. Several engineering projects have been proposed with a view to improving the present critical situation. These projects include underground injections to raise the islands, the construction of new embankments, a reduction in the size of the passes, new access to wide areas for the tide, and the construction of flood gates at the passes. The reliability and effects of these projects are analysed and discussed.In conclusion, the removal of the oil terminal from the lagoon and a stricter control of water pollution are considered the most urgent preliminary actions for a long term solution of the flooding problem. This would enable a decrease in the exchanges between the lagoon and the sea, without, however, reducing the depth of the navigation channels to levels inconsistent with most of the present non-oil traffic. A final measure would be the construction of mobile gates at the passes which would permanently protect the lagoon against flooding.The solution put forward here differs however from the project proposed by a group of experts appointed by the Italian government, which aims at keeping the oil terminal inside the lagoon, thus maintaining the navigation channels at depths which increase hydrodynamic effects and make any sedimetological equilibrium in the lagoon impossible.  相似文献   

Some new results on statistical properties of wind waves     

Paolo Boccotti 《Applied Ocean Research》1983,5(3):134-140

For wind waves modelled by a stationary Gaussian process ζ(t) (ζ = height above m.w.l. of one point of the free surface) it is shown that, in a time interval including an instant t_m where a maximum ζ_m occurs, the ratio between ζ(t) and ζ_m tends with probability approaching one, to the ratio Ψ(t ? t_m)/Ψ(O), as $\text{ζ}{}_{\mathrm{m}}\text{/Ψ}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(}\text{O}\text{)}$ tends to infinity, Ψ(t) being the autocovariance of the process.Starting from this result, it is possible to find analytically the characteristic periods of the highest waves in a sea with a given energy spectrum. These periods, calculated according to period definitions of three methods of wave record analysis, are found to be in remarkably good agreement with data from Bretschneider¹ and Svasek.²  相似文献   

Fish Assemblages in Shallow Marine Caves of the Salento Peninsula (Southern Apulia, SE Italy)   总被引：1，自引：0，他引：1  

Simona Bussotti  Francesco Denitto  Paolo Guidetti  Genuario Belmonte 《Marine Ecology》2002,23(S1):11-20

Abstract. Fish assemblages of three shallow marine caves from the Salento Peninsula (Apulia, SE Italy) were investigated in July 2000. Data were collected in situ by using visual census. A total of nineteen fish species were recorded inside the caves. The species richness generally displayed a similar pattern in all three caves, decreasing from the entrance towards the innermost sections, whereas the patterns of total fish abundance differed among caves. Apogon imberbis (mainly represented by juveniles) was the most important species in terms of number of individuals (accounting for more than 85% of the censused fish) and showed a fairly even distribution inside the investigated caves. Without the numerical contribution of A. imberbis , fish abundance decreased from the entrance to the inner sections and this pattern was common to all three caves. Juvenile fishes of economic interest ( e. g., Diplodus vulgaris and Epinephelus marginatus ) were also recorded inside. The present study suggests that: (1) environmental constraints could affect distribution patterns in fish species richness and in the abundance of several fish along the axis of "blind caves" (with a single entrance), as already observed for sessile benthos and plankton assemblages; (2) shallow marine caves of the Salento Peninsula could exert the role of refuge and/or nursery for some littoral fish species during the adult and/or juvenile stages of their life histories.  相似文献   

Mixed-function oxidase activity and conjugating enzymes in two species of antarctic fish   总被引：1，自引：0，他引：1  

Silvano Focardi  Cristina Fossi  Claudio Leonzio  Paolo Di Simplicio 《Marine environmental research》1989,28(1-4)

Enzyme activities of phase I and phase II of the hepatic detoxication system were investigated in two species of fish from the Ross Sea in Antarctica. The fish had extremely low phase I enzyme (BPMO and aldrin epoxidase). The reductase regenerating enzyme activities were comparable to those found in fish of temperate seas. Transferases of cytosol showed highest activity in the conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) and little or no conjugation of other substrates. The GSSG reductase and the glutathione transferase with peroxidase activity (CuOOH substrate) were low; the Sedependent glutathione peroxidase activity was not detectable. Interspecific differences were found for most of the enzymes tested.  相似文献   

New Development of Eastern Mediterranean Circulation based on Hydrological Observations and Current Measurements   总被引：2，自引：0，他引：2  

Beniamino B. Manca  Laura Ursella  Paolo Scarazzato 《Marine Ecology》2002,23(S1):237-257

Abstract. A number of recent studies based on hydrographic observations and modelling simulations have dealt with the major climatic shift that occurred in the deep circulation of the Eastern Mediterranean. This work presents hydrographic observations and current measurements conducted from 1997 to 1999, which reveal strong modifications in the dynamics of the upper, intermediate and deep layers, as well as an evolution of the thermohaline characteristics of the deep Aegean outflow since 1995. The reversal of the circulation in the upper layer of the north/central Ionian is worthy of note. The observations indicate a reduction of Atlantic Water in the northern Ionian with an increase on the eastern side of the basin. In the intermediate layer, the dispersal path of the Levantine Intermediate Water (LIW) is altered. Highly saline (>39.0) and well-oxygenated intermediate waters were found near the Western Cretan Arc Straits. They flow out from the Aegean, thus interrupting the traditional path of the LIW, and spread prevalently northwards into the Adriatic Sea. In the deep layer, dense waters, exiting from the Adriatic (σ_ø−29.18 kg · m⁻³), flow against the western continental margin in the Ionian Sea at a depth of between 1000–1500 m. Dense waters of Aegean origin (> 29.20 kg · m⁻³), discharged into the central region of the Eastern Mediterranean during the early stages of the transient, propagate prevalently to the east in the Levantine basin and to the west in the northern Ionian Sea. Near-bottom current measurements conducted in the Ionian Sea reveal unforeseen aspects of deep dynamics, suggesting a new configuration of the internal thermohaline conveyor belt of the Eastern Mediterranean.  相似文献   

The measurement of the gravitational constant in an orbiting laboratory     

Paolo Farinella  Andrea Milani  Anna M. Nobili 《Astrophysics and Space Science》1980,73(2):417-433

We propose to measure the gravitational constantG by putting in an orbiting laboratory a known mass of very high density and by tracking the motion of a small test mass under the gravitational influence of the primary mass. We analyse the different sources of perturbation; the consideration of the Earth's gravity gradient leads us to conclude that, if the laboratory is in a low Earth orbit, we cannot get stable satellite-like orbits of the test mass, but we must study only a process of gravitational scattering. In order to maximize the time of interaction it is proposed to use the practical stability of a collinear equilibrium point of the system Earth-primary mass, by putting the test mass as close as possible to the stable manifold of an equilibrium point. This method will allow the determination of the value ofG within a few parts over 10⁵, as shown by some computer simulations of the experiment taking into account also some unknown perturbation and random noise.Two main problems are involved in this experiment: (a) refined numerical methods are needed to take into account all significant perturbations and to extract the result aboutG from the experimental data; (b) during the motion of the test mass, the primary mass must always be free-falling inside the laboratory, so that this experiment needs a drag-free satellite technique of the same type which is necessary for high-precision gravimetric measurements.  相似文献