Book Review: Geodynamics By D. L. Turcotte and G. Schubert, Cambridge University Press, New York, 2002, 456 p., U.S.110 (hb), 110 (hb), 45 (pb) ISBN 0-521-66186-2, 0-521-66624-4.     

Giorgio Ranalli 《Mathematical Geology》2005,37(1):125-126

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Constraints from geochemistry and Sr–Nd isotopes for the origin of albitite deposits from Central Sardinia (Italy)     

Francesca Castorina  Umberto Masi  Giorgio Padalino  Marcella Palomba 《Mineralium Deposita》2006,41(4):323-338

Major- and trace-element contents and Sr–Nd isotope ratios were determined in albitite, albitized and unaltered late-Variscan granitoid samples from the world-class Na-feldspar deposits of central Sardinia, Italy. The albite deposit of high economic grade has geological, textural, and chemical features typical of metasomatic alteration affecting the host granitoids. Albitization, locally accompanied by chloritization and epidotization, was characterized by strong leaching of Mg, Fe, K, and geochemically similar trace elements, and by a significant increase of Na. Ca, and P were moderately leached in the most metasomatized rocks. Other major (Si, Ti, Ca) and trace elements (U, Th, Y, and Zr), along with light (LREE) and middle (MREE) rare-earth elements, behaved essentially immobile at the deposit scale. The Nd-isotope ratios (0.512098 to 0.512248) do not provide information on the emplacement age of the unaltered late-Variscan granitoids. On the other hand, their Sr-isotope ratios fit an errorchron of 274±29 Ma (1σ error), in fair agreement with all published ages of Sardinian Variscan granitoids. The very low Rb content of albitized rocks precludes application of the Rb–Sr radiometric system to determine the age of albitization. The Sm–Nd system is not applicable either, because the ¹⁴³Nd/¹⁴⁴Nd ratios of albitized rocks and unaltered granitoids overlap. The overlap confirms that Sm and Nd were substantially immobile during albitization. On the other hand, the measured ⁸⁷Sr/⁸⁶Sr ratios of the albitized rocks are appreciably lower than those of the unaltered host granitoids, whereas, their initial Sr-isotope ratios are higher. This seems to suggest that a) albitization was induced by non-magmatic fluids rich in radiogenic Sr, and b) albitization occurred shortly after the granitoid emplacement. This conclusion is supported by Nd isotopes, because unaltered granitoids and albitites fit the same reference isochron at 274 Ma. The fluids acquired radiogenic Sr by circulation through the Lower Paleozoic metasedimentary basement. Specifically, it is estimated that Sr supplied by the non-carbonatic basement represents about 22 wt% of total Sr in albitite.  相似文献   

Geochemistry of the Submarine Gaseous Emissions of Panarea (Aeolian Islands, Southern Italy): Magmatic vs. Hydrothermal Origin and Implications for Volcanic Surveillance     

Giovanni Chiodini  Stefano Caliro  Giorgio Caramanna  Domenico Granieri  Carmine Minopoli  Roberto Moretti  Lavinia Perotta  Guido Ventura 《Pure and Applied Geophysics》2006,163(4):759-780

The marine sector surrounding Panarea Island (Aeolian Islands, South Italy) is affected by widespread submarine emissions of CO₂ -rich gases and thermal water discharges which have been known since the Roman Age. On November 3^rd, 2002 an anomalous degassing event affected the area, probably in response to a submarine explosion. The concentrations of minor reactive gases (CO, CH₄ and H₂) of samples collected in November and December, 2002 show drastic compositional changes when compared to previous samples collected from the same area in the 1980s. In particular the samples collected after the November 3^rd phenomenon display relative increases in H₂ and CO and a strong decrease in the CH₄ contents, while other gas species show no significant change. The interaction of the original gas with seawater explains the variable contents of CO₂, H₂S, N₂, Ar and He which characterize the different samples, but cannot explain the large variations of CO, CH₄ and H₂ which are instead compatible with changes in the redox, temperature and pressure conditions of the system. Two models, both implying an increasing input of magmatic fluids are compatible with the observed variations of minor reactive species. In the first one, the input of magmatic fluids drives the hydrothermal system towards atypical (more oxidizing) redox conditions, slowly pressurizing the system up to a critical state. In the second one, the hydrothermal system is flashed by the rising high-T volcanic fluid, suddenly released by a magmatic body at depth. The two models have different implications for volcanic surveillance and risk assessment: In the first case, the November 3^rd event may represent both the culmination of a relatively slow process which caused the overpressurization of the hydrothermal system and the beginning of a new phase of quiescence. The possible evolution of the second model is unforeseeable because it is mainly related to the thermal, baric and compositional state of the deep magmatic system that is poorly known.  相似文献   

The basal ash deposit of the Sovana Eruption (Vulsini Volcanoes, central Italy): the product of a dilute pyroclastic density current     

D. M. Palladino  J. Taddeucci 《Journal of Volcanology and Geothermal Research》1998,87(1-4)

A low aspect ratio, decimeter-thick ash deposit, axisymmetrically distributed around the Latera Caldera (Western Vulsini Volcanoes, central Italy) has been studied by means of field and laboratory investigations. Field studies comprise facies analysis at centimeter scale and maximum clast size and deposit thickness measurements. Grain size and component distribution, chemical composition and particle morphoscopic features have been determined on selected samples. We discuss the co-ignimbrite ash fall vs. pyroclastic surge origin of the deposit and the hydrovolcanic vs. magmatic eruption nature. Complex facies association, textural features and grain size data rule out an ash fall origin for the whole deposit. The hydrovolcanic nature of the eruption has been discarded on the grounds of componentry and morphoscopic features of vitric fragments. We propose that the main body of the ash deposit formed from a radially expanding, dilute, turbulent pyroclastic density current, originated by a continuous collapse of a low-altitude (a few kilometers) eruptive column with a possible radial jet component.  相似文献   

Stresses and velocities in orogenic wedges with power-law rheology and linearly varying longitudinal strain rate     

Jiyang Liu  Giorgio Ranalli 《Journal of Structural Geology》1998,20(12):1611-1623

A two-dimensional analytical solution for stress, strain rate, and velocity is obtained for parallel-sided and wedge-shaped blocks with generalized viscous rheology (linearly viscous and power-law) deforming in plane strain. The main assumptions used in the derivation of the solution are that the material is incompressible, the longitudinal gradient in shear stress is much less than the vertical gradient of vertical normal stress, and the longitudinal strain rate varies linearly in the horizontal direction. Velocity boundary conditions are specified at the top of the block, and shear stress boundary conditions at the base of the block. In the one-dimensional case (where stress and strain rate do not vary in the longitudinal direction), the solution reduces to a well-known solution for the deformation of parallel-sided ice sheets [Nye, J. F. (1957) The distribution of stress and velocity in glaciers and ice sheets. Proceedings of the Royal Society of London A-239, 113–133]. The stress equilibrium for tapered wedges [Platt, J. P. (1986) Dynamics of orogenic wedges and the uplift of high-pressure metamorphic rocks. Geological Society of America Bulletin 97, 1037–1053] is a special case of the present stress solution. Implementation of the solution requires the subdivision of the wedge into vertical segments, and yields the tectonic normal and shear stresses that must be applied to the rear of a block with specified rheology in order to maintain a given longitudinal strain rate. The solution makes it possible to model deformation patterns analytically with longitudinally varying strain rate (including coeval compression and extension) and with vertical components of velocity reflecting the effects of underplating.  相似文献   

Analysis and Estimation of Natural Processes with Nonhomogeneous Spatial Variation Using Secondary Information   总被引：1，自引：0，他引：1  

Giorgio Cassiani  George Christakos 《Mathematical Geology》1998,30(1):57-76

Natural processes encountered in mining, hydrogeologic, environmental, etc. applications usually are poorly known because of scarcity of data over the area of interest. Therefore, stochastic estimation techniques are the tool of choice for a careful accounting of the heterogeneity and uncertainty involved. Within such a framework, a better utilization of all available data concerning the process of interest and all other natural processes related to it, is of primary importance. Because many natural processes show complicated spatial trends, the hypothesis of spatial homogeneity cannot be invoked always, and the more general theory of intrinsic spatial random fields should be employed. Efficient use of secondary information in terms of the intrinsic model requires that suitable permissibility criteria for the generalized covariances and cross-covariances are satisfied. A set of permissibility criteria are presented for the situation of two intrinsic random fields. These criteria are more general and comprehensive than the ones currently available in the geostatistical literature. A constrained least-square technique is implemented for the inference of the generalized covariance and cross-covariance parameters, and a synthetic example is used to illustrate the methodology. The numerical results show that the use of secondary information can lead to significant reductions in the estimation errors.  相似文献   

Incorporating Auxiliary Geophysical Data into Ground-Water Flow Parameter Estimation   总被引：1，自引：0，他引：1  

Giorgio Cassiani  Miguel A. Medina  Jr. 《Ground water》1997,35(1):79-91

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Sodar retrieval of vertical acceleration, and implications for the determination of temperature and fluxes in the convective boundary layer     

Giorgio Fiocco  Maria Grazia Ciminelli  Giangiuseppe Mastrantonio 《Atmospheric Research》1986,20(2-4)

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Comment on “analysis of nonintrinsic spatial variability by residual kriging with application to regional groundwater levels” by Shlomo P. Neuman and Elizabeth A. Jacobson     

Giuseppe Gambolati  Giorgio Galeati 《Mathematical Geosciences》1987,19(3):249-257

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Die Eigenschwingungen der durch den Kanal im Damm von Melide gekoppelten Becken des Luganersees     

Jürg Trösch  Giorgio Salvadè  Kurt Stocker 《Aquatic Sciences - Research Across Boundaries》1987,49(1):16-28

The northern and the southern basin of Lake Lugano, Switzerland, are separated by an artificial dam. The flow of the water is not only influenced by the outflow of the northern basin but also by gravitational oscillations (seiches) of both basins. A longperiodic peak around 100 minutes can be explained by a mathematical model. The interaction of the internal waves is a coupled oscillation with a period of 74 hours.   相似文献