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171.
172.
Merlin Méheut Michele Lazzeri Francesco Mauri 《Geochimica et cosmochimica acta》2007,71(13):3170-3181
Isotopic fractionation factors for oxygen, hydrogen and silicon have been calculated using first-principles methods for the kaolinite, quartz, water (ice and gas water) system. Good agreement between theory and experiment is obtained for mineral-water oxygen isotope fractionation. This approach gives reliable results on isotopic fractionation factors as a function of temperature, within a relative precision of typically 5%. These calculations provide independent quantitative constraints on the internal fractionation of oxygen in kaolinite, the fractionation of silicon isotopes at equilibrium, or hydrogen fractionation between kaolinite and water. Calculated fractionation factors at 300 K are 12.5‰ for the kaolinite internal-fractionation of oxygen, and 1.6‰ for silicon fractionation between quartz and kaolinite. 相似文献
173.
Salvatore Grimaldi Fernando Nardi Francesco Di Benedetto Erkan Istanbulluoglu Rafael L. Bras 《Advances in water resources》2007
Spurious pits in digital elevation models (DEMs) are traditionally removed by filling depressions, often creating flat regions that lead to inaccurate estimation of landscape flow directions. In this study, a physical approach based on a simple landscape evolution model is proposed for DEM pit removal. This method, an alternative to traditional geometrical procedures, enforces more realistic slopes and flow directions on topography. The procedure is compared with the method most commonly used in the literature and distributed with commercial GIS software where, generally, elevations of a depression are increased up to the lowest value among neighbouring cells. Several tests are performed and parameters sensitivity is carried out in order to demonstrate the performance of the proposed model as compared to traditional methods. 相似文献
174.
Alessandro Bonforte Salvatore Gambino Francesco Guglielmino Francesco Obrizzo Mimmo Palano Giuseppe Puglisi 《Bulletin of Volcanology》2007,69(7):757-768
On 22 September 2002, 1 month before the beginning of the flank eruption on the NE Rift, an M-3.7 earthquake struck the northeastern
part of Mt. Etna, on the westernmost part of the Pernicana fault. In order to investigate the ground deformation pattern associated
with this event, a multi-disciplinary approach is presented here. Just after the earthquake, specific GPS surveys were carried
out on two small sub-networks, aimed at monitoring the eastern part of the Pernicana fault, and some baselines belonging to
the northeastern EDM monitoring network of Mt. Etna were measured. The leveling route on the northeastern flank of the volcano
was also surveyed. Furthermore, an investigation using SAR interferometry was performed and also the continuous tilt data
recorded at a high precision sensor close to the epicenter were analyzed to constrain the coseismic deformation. The results
of the geodetic surveys show a ground deformation pattern that affects the entire northeastern flank of the volcano, clearly
shaped by the Pernicana fault, but too strong and wide to be related only to an M-3.7 earthquake. Leveling and DInSAR data
highlight a local strong subsidence, up to 7 cm, close to the Pernicana fault. Significant displacements, up to 2 cm, were
also detected on the upper part of the NE Rift and in the summit craters area, while the displacements decrease at lower altitude,
suggesting that the dislocation did not continue further eastward. Three-dimensional GPS data inversions have been attempted
in order to model the ground deformation source and its relationship with the volcano plumbing system. The model has also
been constrained by vertical displacements measured by the leveling survey and by the deformation map obtained by SAR interferometry. 相似文献
175.
176.
Davide Lenaz Vadim S. Kamenetsky Anthony J. Crawford Francesco Princivalle 《Contributions to Mineralogy and Petrology》2000,139(6):748-758
Detrital spinel is a widespread heavy mineral in sandstones from the Maastrichtian–Middle Eocene sedimentary basins in the
SE Alps. Chemistry of detrital spinels from the Claut/Clauzetto and Julian Basins (N Italy and NW Slovenia) is used to constrain
petrological and geochemical affinities and tectonic provenance of the source rocks. In addition, we have analysed melt inclusion
compositions in the detrital volcanic spinels to better constrain the nature of their parental magmas. This is the first study
of melt inclusions in detrital spinels. Two principal compositional groups of detrital spinels are recognised based on their
TiO2 and Fe2+/Fe3+; one derived from peridotites, the other from basaltic volcanics. Peridotitic spinels are more abundant and have TiO2 < 0.2 wt% and high Cr/Cr + Al (40–90), characteristic of suprasubduction zone harzburgites. Significant chemical variations
among volcanic spinels (TiO2 up to 3 wt%, Al2O3 12–44 wt%) suggest multiple sources, with geochemically distinct characteristics, including MORB-type and backarc basin basalts,
subduction-related magmas and tholeiites produced during early continental rifting. Compositions of homogenised melt inclusions
in spinels with TiO2 > 0.2 better distinguish the differences between the compositions of their host spinels and help to further clarify the geodynamic
provenance of extrusive source rocks. Several compositional groups of melt inclusions have been recognised and represent diverse
magmatism of marginal basins, including MORB- and subduction-related geochemical types, as well as magmas characteristic of
early continental rifting. These results, combined with the data on regional ophiolitic complexes and tectonic reconstructions
favour the Internal Dinarides of Yugoslavia as a possible source area for the SE Alps sediments.
Received: 20 January 2000 / Accepted: 25 April 2000 相似文献
177.
Francesco Princivalle Gabriella Salviulo Andrea Marzoli Enzo M. Piccirillo 《Contributions to Mineralogy and Petrology》2000,139(5):503-508
The crystal chemistry of six clinopyroxenes enclosed in protogranular spinel-peridotite mantle xenoliths from Lake Nji (Cameroon,
W Africa) was studied by means of single-crystal X-ray diffraction and electron microprobe. These spinel-peridotite xenoliths
are characterised by clinopyroxene contents distinctly higher than those reported by Lee et al. (1996) for spinel-peridotite
xenoliths of the same region (19–11% and 15–8% respectively) and by high clinopyroxene/orthopyroxene ratios: 0.7–2.7 (present
study) and about 0.4 (Lee et al. 1996). The clinopyroxene crystal chemistry indicates that the xenoliths show the compositional
features of a mantle source contaminated by small-volume melts, responsible for the high clinopyroxene content. The protogranular
texture of the Cameroon xenoliths (upper portion of lithospheric mantle) testifies that the spinel peridotite and the associated
small-volume melts completely re-equilibrated at the spinel-peridotite facies. This is also supported by the petrological
and geochemical data of Lee et al. (1996) on the Etinde–Biu Plateau spinel-peridotite xenoliths, which underwent Late Proterozoic–Early
Paleozoic enrichment in incompatible trace elements.
Received: 6 October 1999 / Accepted: 27 March 2000 相似文献
178.
179.
Large scale climate and rainfall seasonality in a Mediterranean Area: Insights from a non‐homogeneous Markov model applied to the Agro‐Pontino plain
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Francesco Cioffi Federico Conticello Upmanu Lall Lucia Marotta Vito Telesca 《水文研究》2017,31(3):668-686
In the context of climate change and variability, there is considerable interest in how large scale climate indicators influence regional precipitation occurrence and its seasonality. Seasonal and longer climate projections from coupled ocean–atmosphere models need to be downscaled to regional levels for hydrologic applications, and the identification of appropriate state variables from such models that can best inform this process is also of direct interest. Here, a Non‐Homogeneous Hidden Markov Model (NHMM) for downscaling daily rainfall is developed for the Agro‐Pontino Plain, a coastal reclamation region very vulnerable to changes of hydrological cycle. The NHMM, through a set of atmospheric predictors, provides the link between large scale meteorological features and local rainfall patterns. Atmospheric data from the NCEP/NCAR archive and 56‐years record (1951–2004) of daily rainfall measurements from 7 stations in Agro‐Pontino Plain are analyzed. A number of validation tests are carried out, in order to: 1) identify the best set of atmospheric predictors to model local rainfall; 2) evaluate the model performance to capture realistically relevant rainfall attributes as the inter‐annual and seasonal variability, as well as average and extreme rainfall patterns. Validation tests show that the best set of atmospheric predictors are the following: mean sea level pressure, temperature at 1000 hPa, meridional and zonal wind at 850 hPa and precipitable water, from 20°N to 80°N of latitude and from 80°W to 60°E of longitude. Furthermore, the validation tests show that the rainfall attributes are simulated realistically and accurately. The capability of the NHMM to be used as a forecasting tool to quantify changes of rainfall patterns forced by alteration of atmospheric circulation under climate change and variability scenarios is discussed. 相似文献
180.
The effect of low‐permeability fault zones on groundwater flow in a compartmentalized system. Experimental evidence from a carbonate aquifer (Southern Italy)
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The hydrogeological behaviour of fault zones in carbonate aquifers is often neglected in conceptual and numerical models. Furthermore, no information is available regarding the relationships between piezometric levels when significant compartmentalization occurs due to the occurrence of low‐flow fault zones. The aim of this study was to refine the conceptualization of subsurface flow in faulted carbonate aquifers and to analyse relationships between sub‐basins within a compartmentalized aquifer system in Southern Italy. The interactions between compartments that straddle low‐flow faults were investigated over four hydrologic years using a statistical approach to compare (i) the hydraulic heads within two wells located up‐ and down‐gradient of tectonic discontinuities as well as (ii) the rainfall and piezometric levels. The results of this study suggest that a set of barriers exists between the wells, and, therefore, the total head loss observed between the wells (approximately 80 m) should be distributed across several aquitards, with one aquitard exhibiting a relatively high permeability or low degree of integrity. Due to slight differences in permeability, transient conditions in aquitards can occur over relatively short periods, which is in agreement with the results of the statistical data analysis. Consequently, rather than being caused by pure aquitards, aquifer system compartmentalization likely results from slight differences in the permeability between lower‐permeability fault zones and adjacent higher‐permeability protoliths. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献