Microstructures associated with static and dynamic recrystallization of Carrara marble (Alpi Apuane,NW Tuscany,Italy)   总被引：2，自引：0，他引：2  

Molli  Giancarlo  Heilbronner  Renée 《Geologie en Mijnbouw》1999,78(1):119-126

The present contribution summarizes the first results of a study focusing on microstructures from Alpi Apuane marbles. Its aim is both an analysis of the evolution of the metamorphic complex recorded in marbles and the supply of basic material for process-oriented studies on calcite microstructures due to natural deformation. Quantitative analysis of the variations of statically recrystallized microstructures suggest a relationship with the peak metamorphic temperatures. Previously unrecognized post-thermal peak shear zones, showing overprint microstructures typical of grain-boundary migration and dynamic recrystallization, are described; they document the natural deformation of Carrara marble.  相似文献   

Understanding hydrological processes in glacierized catchments: Evidence and implications of highly variable isotopic and electrical conductivity data     

Giulia Zuecco  Luca Carturan  Fabrizio De Blasi  Roberto Seppi  Thomas Zanoner  Daniele Penna  Marco Borga  Alberto Carton  Giancarlo Dalla Fontana 《水文研究》2019,33(5):816-832

The spatial and temporal characterization of geochemical tracers over Alpine glacierized catchments is particularly difficult, but fundamental to quantify groundwater, glacier melt, and rain water contribution to stream runoff. In this study, we analysed the spatial and temporal variability of δ²H and electrical conductivity (EC) in various water sources during three ablation seasons in an 8.4‐km² glacierized catchment in the Italian Alps, in relation to snow cover and hydro‐meteorological conditions. Variations in the daily streamflow range due to melt‐induced runoff events were controlled by maximum daily air temperature and snow covered area in the catchment. Maximum daily streamflow decreased with increasing snow cover, and a threshold relation was found between maximum daily temperature and daily streamflow range. During melt‐induced runoff events, stream water EC decreased due to the contribution of glacier melt water to stream runoff. In this catchment, EC could be used to distinguish the contribution of subglacial flow (identified as an end member, enriched in EC) from glacier melt water to stream runoff, whereas spring water in the study area could not be considered as an end member. The isotopic composition of snow, glacier ice, and melt water was not significantly correlated with the sampling point elevation, and the spatial variability was more likely affected by postdepositional processes. The high spatial and temporal variability in the tracer signature of the end members (subglacial flow, rain water, glacier melt water, and residual winter snow), together with small daily variability in stream water δ²H dynamics, are problematic for the quantification of the contribution of the identified end members to stream runoff, and call for further research, possibly integrated with other natural or artificial tracers.  相似文献   

Finite element evaluation of the effects of faulting on a shallow tunnel in alluvial soil     

Annamaria Cividini  Giancarlo Gioda  Vincenzo Petrini 《Acta Geotechnica》2010,5(2):113-120

A numerical estimation is presented on the effects induced in an existing tunnel by the development of a fault from the deep bedrock during a seismic event. The spreading of the fault within the alluvial deposit hosting the tunnel, and the consequent effects on its permanent liner, are studied in static conditions through a series of elastic-plastic, plane strain finite element analyses. They account for the reduction of the shear strength and stiffness characteristics of the faulting zone with increasing irreversible strains. Even though the calculations require only “standard”, e.g. peak and residual, material parameters it is shown that these properties can hardly be obtained for the alluvial deposit at hand. To overcome this drawback a relatively large scale in-situ tests could be performed and its results could be interpreted through a suitable back analysis. This would permit characterizing the numerical model to be subsequently adopted for the analysis of the faulting process.  相似文献   

Constraints on primordial non-Gaussianity from a needlet analysis of the WMAP-5 data     

Davide Pietrobon  Paolo Cabella  Amedeo Balbi  Giancarlo de Gasperis  Nicola Vittorio 《Monthly notices of the Royal Astronomical Society》2009,396(3):1682-1688

We look for a non-Gaussian signal in the Wilkinson Microwave Anisotropy Probe ( WMAP ) 5-year temperature anisotropy maps by performing a needlet-based data analysis. We use the foreground-reduced maps obtained by the WMAP team through the optimal combination of the W, V and Q channels, and perform realistic non-Gaussian simulations in order to constrain the non-linear coupling parameter f _NL. We apply a third-order estimator of the needlet coefficients skewness and compute the  χ²  statistics of its distribution. We obtain  −80 < f _NL < 120  at 95 per cent confidence level, which is consistent with a Gaussian distribution and comparable to previous constraints on the non-linear coupling. We then develop an estimator of f _NL based on the same simulations and we find consistent constraints on primordial non-Gaussianity. We finally compute the three-point correlation function in needlet space: the constraints on f _NL improve to  −50 < f _NL < 110  at 95 per cent confidence level.  相似文献   

Optical afterglows of gamma-ray bursts: a bimodal distribution?     

Marco Nardini  Gabriele Ghisellini  Giancarlo Ghirlanda 《Monthly notices of the Royal Astronomical Society》2008,383(3):1049-1057

The luminosities of the optical afterglows of gamma-ray bursts, 12 h (rest-frame time) after the trigger, show a surprising clustering, with a minority of events being at a significantly smaller luminosity. If real, this dichotomy would be a crucial clue to understand the nature of optically dark afterglows, i.e. bursts that are detected in the X-ray band, but not in the optical. We investigate this issue by studying bursts of the pre- Swift era, both detected and undetected in the optical. The limiting magnitudes of the undetected ones are used to construct the probability that a generic burst is observed down to a given magnitude limit. Then, by simulating a large number of bursts with pre-assigned characteristics, we can compare the properties of the observed optical luminosity distribution with the simulated one. Our results suggest that the hints of bimodality present in the observed distribution reflect a real bimodality: either the optical luminosity distribution of bursts is intrinsically bimodal, or there exists a population of bursts with a quite significant grey absorption, i.e. wavelength-independent extinction. This population of intrinsically weak or grey-absorbed events can be associated with dark bursts.  相似文献   

A structural study of cyanotrichite from Dachang by conventional and automated electron diffraction     

Gennaro Ventruti  Enrico Mugnaioli  Giancarlo Capitani  Fernando Scordari  Daniela Pinto  Andrea Lausi 《Physics and Chemistry of Minerals》2015,42(8):651-661

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Estuarine Biotope Mosaics and Habitat Management Goals: An Application in Tampa Bay,FL, USA   总被引：1，自引：0，他引：1  

Giancarlo Cicchetti  Holly Greening 《Estuaries and Coasts》2011,34(6):1278-1292

Many types of anthropogenic stress to estuaries lead to destruction and conversion of habitats, thus altering habitat landscapes and changing the “arena” in which the life history interactions of native fauna take place. This can lead to decreased populations of valued fauna and other negative consequences. The Tampa Bay Estuary Program (TBEP) pioneered a system-wide management framework that develops estuarine habitat restoration and protection goals based on supporting estuarine-dependent species and the habitat landscapes they require (for example, the extent of seagrass beds, mangrove forests, oyster reefs, or oligohaline marshes) within an estuary. We describe this framework and provide related statistics as methods to help managers set system-wide ecological goals using larger conceptual approaches that are easily communicated to stakeholders and the public; we also discuss applications of the approach to existing and evolving paradigms of estuarine management. The TBEP and partners used this framework to combine a simple and unifying vision with a diverse and complex set of management tools, resulting in greatly improved environmental conditions within Tampa Bay.  相似文献   

Superimposed brittle structures in the late-orogenic extension of the Northern Apennine: results from the Carrara area (Alpi Apuane, NW Tuscany)     

G. Ottria  & G. Molli 《地学学报》2000,12(2):52-59

This paper presents data on the geometric and kinematic features of brittle faults in the Carrara area (Alpi Apuane, NW Tuscany, Italy), providing the first paleostress determination in a key region of the Northern Apennine. Meso-and microfault analyses point out the presence of brittle structures formed during a polyphase deformation and characterized by an older stage (DS1), with an interfering system of strike slip and normal faulting, followed by the DS2 stage developing normal faults locally showing apenninic trend (NW/SE). As a whole, the brittle structures are related to the late Pliocene–middle Pleistocene evolution of the Thyrrenian side of the Northern Apennine.  相似文献   

Stratigraphy, chronology, and sedimentology of ignimbrites from the white trachytic tuff, Roccamonfina Volcano, Italy     

Bernardino Giannetti  Giancarlo De Casa 《Journal of Volcanology and Geothermal Research》2000,96(3-4)

We describe the stratigraphy, chronology, and grain size characteristics of the white trachytic tuff (WTT) of Roccamonfina Volcano (Italy). The pyroclastic rock was emplaced between 317 and 230 Ma BP during seven major eruptive events (units A to G) and three minor events (units BC, CD, and DE). These units are separated by paleosol layers and compositionally well-differentiated pyroclastic successions. Stratigraphic control is favored by the occurrence at the base of major units of marker layers. Four WTT units (1 to 4) occur within the central caldera. These are not positively correlated with specific extracaldera units.The source of most of the WTT units was the central caldera. Units B and C were controlled by the western wall of the caldera, whereas units D and E were able to overcome this barrier, spreading symmetrically along the flanks of MC. The maximum pumice size (MP) of units increases with distance from the caldera, whereas the maximum lithic size (ML) decreases. MP and ML of the marker layer of unit D (MKDa–MKDp) do not show any systematic variations with respect to the central caldera. In contrast, the thickness of surge MKDa decreases with distance from the source, and MKDp accumulates to the north of MC probably controlled, respectively, by mobility-transport power and by wind blowing northwards.The grain size characteristics of the WTT deposits are used for classifying the units. There is no systematic variation of the grain size as a function of stratigraphic height either among units or within single units. Large variation of components in subunit E1, with repetitive alternation of pyroclastic flow to surge through fallout vs. surge deposits, suggests that the process of eruption took place in a complex or piecemeal fashion.Pumice concentration zones (PCZ) occur at all WTT levels on the volcano, but they are much thicker and pumice clasts are much larger within the central caldera. These were probably originated by the disruption of lava (flow or dome) to pumice fragments and fine ash due to sudden depressurization and interaction with lake waters of the molten lava. Local basal PCZ are, in some cases, similar to the lapilli-rich “layer 1P” that has been described elsewhere, and may have been deposited from currents transitional between pyroclastic surge and flow. Other basal PCZ formed in response to small undulations in the substrate, or can be originated by fallout. Lenticular PCZ within ignimbrite interiors and tops are interpreted to record marginal pumice levees and pumice rafts, some of which were buried by subsequant pyroclastic flows.Lithic concentration zones (LCZ) also occur at various stratigraphic height within the extracaldera ignimbrites, whereas intracaldera LCZ are absent, probably due to the fact that ignimbrite currents are strongly energetic and erosive near vent. LCZ at the top of basal inversely graded layers are formed by mechanical sieving or dispersive pressure in response to variable velocity gradients and particle concentration gradients (a segregation process). Coarse LCZ and coarse lithic breccias (LB), that reside in the interior or tops of pyroclastic flows and that occur in medial to distal areas, are interpreted to be the result of slugs of lithic-rich debris introduced by vent collapse or rockslides into the moving pyroclastic flows along their flow paths. These LCZ become mixed to varying degrees due to differential densities and velocities relative to the pyroclastic flows (desegregation processes).  相似文献   

Book reviews     

G. A. Chapman  Giancarlo Noci  J. J. Rickard 《Solar physics》1992,142(2):415-417

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