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101.
102.
Matteo Lelli Sergio Grassi Michele Amadori Fabrizio Franceschini 《Environmental Earth Sciences》2014,71(9):3907-3919
A detailed hydrogeochemical study of groundwater in the Cecina coastal plain (Livorno province, Italy) and its inner sectors was undertaken in 2008, as chemical analyses carried out on groundwater since 2006 have revealed Cr(VI) concentrations of up to 49 μg/L (well above the permissible limit of 5 μg/L). Ophiolite outcrops are present throughout the study area, and their fragments likely represent a significant portion of the existing multilayered aquifer skeleton. Waters delivered by the serpentinite outcrops have a typically Mg–HCO3 composition, whereas those of the coastal plain are prevailingly of the Ca/Mg–HCO3 type with significant Mg contents. Significant NO3 contamination characterises the studied coastal plain, and an interesting negative correlation exists between Cr(VI) and both NO3 and SO4 deriving from the widespread use of (NH4)2SO4 as a farm fertilizer. Chromium speciation calculations carried out using the EQ3NR code reveal that the prevailing Cr(VI) species in solution is CrO4 2?; however, CaCrO4° and MgCrO4° neutral complexes represent significant percentages (up to 42 %). These findings suggest that the mobility and consequently the bioavailability of Cr(VI) can be significantly enhanced by these neutral complexes, which are not considered to be affected by adsorption/desorption processes. The Cr(VI) source, investigated by means of the Mg/SiO2 molar ratio, seems to be represented mainly by Mg-bearing minerals of the chlorite group. Petrographic observations confirm the occurrence of this mineral group. The interaction between rainwater and the local serpentinite rock was simulated at different $P_{{{\text{CO}}_{ 2} }}$ and $P_{{{\text{O}}_{ 2} }}$ conditions by reaction path modelling using the EQ3/6 software package. $P_{{{\text{O}}_{ 2} }}$ was varied in accordance with the assumption that redox conditions are determined in part by NO3. Results are in good agreement with experimental data on spring waters and subordinately with data on some coastal plain groundwater, which plot in a rather wide $P_{{{\text{CO}}_{ 2} }}$ and $P_{{{\text{O}}_{ 2} }}$ field. Although the dissolved Cr content is mostly of natural origin, fertilization may affect its fate. 相似文献
103.
Geoffrey D. Bromiley Fabrizio Nestola Ming Zhang 《Geochimica et cosmochimica acta》2010,74(2):705-445
The solubility and incorporation mechanisms of water in synthetic and natural MgAl2O4 spinel have been investigated in a series of high-pressure/temperature annealing experiments. In contrast to most other nominally anhydrous minerals, natural spinel appears to be completely anhydrous. On the other hand, non-stoichiometric Al-rich synthetic (defect) spinel can accommodate several hundred ppm water in the form of structurally-incorporated hydrogen. Infrared (IR) spectra of hydrated defect spinel contain one main O-H stretching band at 3343-3352 cm−1 and a doublet consisting of two distinct O-H bands at 3505-3517 cm−1 and 3557-3566 cm−1. IR spectra and structural refinements based on single-crystal X-ray data are consistent with hydrogen incorporation in defect spinel onto both octahedral and tetrahedral O-O edges. Fine structure of O-H bands in IR spectra can be explained by partial coupling of interstitial hydrogen with cation vacancies, or by the effects of Mg-Al disorder on the tetrahedral site. The concentration of cation vacancies in defect spinel is a major control on hydrogen affinity. The commercial availability of large single crystals of defect spinel coupled with high water solubility and similarities in water incorporation mechanisms between hydrous defect spinel and hydrous ringwoodite (Mg2SiO4) suggests that synthetic defect spinel may be a useful low-pressure analogue material for investigating the causes and consequences of water incorporation in the lower part of Earth’s mantle transition zone. 相似文献
104.
Antigorite equation of state and anomalous softening at 6 GPa: an in situ single-crystal X-ray diffraction study 总被引:1,自引:0,他引:1
Fabrizio Nestola Ross J. Angel Jing Zhao Carlos J. Garrido Vicente López Sánchez-Vizcaíno Giancarlo Capitani Marcello Mellini 《Contributions to Mineralogy and Petrology》2010,160(1):33-43
The compressibility of antigorite has been determined up to 8.826(8) GPa, for the first time by single crystal X-ray diffraction in a diamond anvil cell, on a specimen from Cerro del Almirez. Fifteen pressure–volume data, up to 5.910(6) GPa, have been fit by a third-order Birch–Murnaghan equation of state, yielding V 0 = 2,914.07(23) Å3, K T0 = 62.9(4) GPa, with K′ = 6.1(2). The compression of antigorite is very anisotropic with axial compressibilities in the ratio 1.11:1.00:3.22 along a, b and c, respectively. The new equation of state leads to an estimation of the upper stability limit of antigorite that is intermediate with respect to existing values, and in better agreement with experiments. At pressures in excess of 6 GPa antigorite displays a significant volume softening that may be relevant for very cold subducting slabs. 相似文献
105.
Massimo Cerdonio Fabrizio De Marchi Roberto De Pietri Philippe Jetzer Francesco Marzari Giulio Mazzolo Antonello Ortolan Mauro Sereno 《Celestial Mechanics and Dynamical Astronomy》2010,107(1-2):255-264
The analysis of non-radiative sources of static or time-dependent gravitational fields in the Solar System is crucial to accurately estimate the free-fall orbits of the LISA space mission. In particular, we take into account the gravitational effects of Interplanetary Dust (ID) on the spacecraft trajectories. The perturbing gravitational field has been calculated for some ID density distributions that fit the observed zodiacal light. Then we integrated the Gauss planetary equations to get the deviations from the LISA Keplerian orbits around the Sun. This analysis can be eventually extended to Local Dark Matter (LDM), as gravitational fields are expected to be similar for ID and LDM distributions. Under some strong assumptions on the displacement noise at very low frequency, the Doppler data collected during the whole LISA mission could provide upper limits on ID and LDM densities. 相似文献
106.
The stratigraphic correlation of North and Equatorial Atlantic Ocean records with Mediterranean astronomically tuned sections reveals the diachrony of several planktonic foraminiferal bioevents, but shows the possibility to adopt the Mediterranean biostratigraphy in North Atlantic records. These data provide new tools for biostratigraphic correlation, mainly between the Mediterranean and the North Atlantic areas. Quantitative analyses carried out on planktonic foraminifera reveal the occurrence at Site 982-HoleB (ODP Leg 162) of some bioevents in the same order as those recorded in Mediterranean sequences. In addition, Neogloboquadrina atlantica praeatlantica first occurrence (FO) [within the short range of Paragloborotalia mayeri, sensuRiv. Ital. Paleontol. Stratigr. 108 (2002) 257] occurs in levels older than its FO in the Mediterranean area where it first appears at the same level as N. acostaensis s.s. coinciding with the last occurrence of P. partimlabiata. In agreement with the findings of Poore [Init. Rep. Deep Sea Drilling Proj. 49 (1979) 447] and the hypothesis of Zachariasse and Aubry [Paleobios 16 (1994) 68], the first representative of the neogloboquadrinids originated north of Iceland and migrated towards the southern latitudes at different times, first in the Mediterranean and mid-latitude Atlantic Ocean, then in low-latitudes (Site 397). 相似文献
107.
Marco F. Nisi Fabrizio Antonioli Giuseppe Dai Pra Gabriele Leoni Sergio Silenzi 《第四纪科学杂志》2003,18(8):709-721
The opening of the north‐central Tyrrhenian Sea is the result of the Cretaceous–Paleogene alpine collision, which triggered a series of regional uplift, subsidence and transcurrent tectonic mechanisms along the coastal Tyrrhenian sectors of peninsular Italy. These tectonic processes, in conjunction with the effects of glacio‐ and hydro‐isostasy during the Quaternary, produced substantial crustal responses that, in some cases, reached metres in extent. In the study of coastal neotectonics, geomorphological markers of the last interglacial maximum, corresponding to marine isotope stage 5.5, are generally used to quantify the magnitude of the vertical crustal displacements that have occurred since 125 kyr. Through altimetrical, palaeoenvironmental and chronological reinterpretation of the most significant works published since 1913, combined with an additional set of data reported here, a detailed reconstruction of the shoreline displacements evident along 500 km of coast between northern Tuscany and southern Latium is presented. The reconstruction was carried out by quantifying the vertical movement since the last interglacial period and by identifying the tectonic behaviour of different coastal sectors. This has been done by carefully choosing the eustatic marker, among those available at each study site, in order to minimize the margin of error associated with the measurements. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
108.
Stefano Gori Biagio Giaccio Fabrizio Galadini Emanuela Falcucci Paolo Messina Andrea Sposato Francesco Dramis 《International Journal of Earth Sciences》2011,100(1):157-171
In the present work we analyse one of the active normal faults affecting the central Apennines, i.e. the Mt. Morrone normal
fault system. This tectonic structure, which comprises two parallel, NW-SE trending fault segments, is considered as potentially
responsible for earthquakes of magnitude ≥ 6.5 and its last activation probably occurred during the second century AD. Structural
observations performed along the fault planes have allowed to define the mainly normal kinematics of the tectonic structure,
fitting an approximately N 20° trending extensional deformation. Geological and geomorphological investigations performed
along the whole Mt. Morrone south-western slopes permitted us to identify the displacement of alluvial fans, attributed to
Middle and Late Pleistocene by means of tephro-stratigraphic analyses and geomorphological correlations with dated lacustrine
sequences, along the western fault branch. This allowed to evaluate in 0.4 ± 0.07 mm/year the slip rate of this segment. On
the other hand, the lack of synchronous landforms and/or deposits that can be correlated across the eastern fault segment
prevented the definition of the slip rate related to this fault branch. Nevertheless, basing on a critical review of the available
literature dealing with normal fault systems evolution, we hypothesised a total slip rate of the fault system in the range
of 0.4 ± 0.07 to 0.8 ± 0.09 mm/year. Moreover, basing on the length at surface of the Mt. Morrone fault system (i.e. 22–23 km)
we estimated the maximum expected magnitude of an earthquake that might originate along this tectonic structure in the order
of 6.6–6.7. 相似文献
109.
Here we report the first observations of loggerhead turtles Caretta caretta preying on a conspicuous molluscan invader, the rapa whelk Rapana venosa. An average number of 136 opercula were found in stomach contents of five turtles, the curved carapace length ranging in from 51 to 112 cm. No other alimentary items were found in the turtles analyzed. We suggest that the rapa whelk may constitute up to 100% of the diet for immature and mature loggerheads in the Río de la Plata estuary (Uruguay), highlighting the plastic nature of the foraging behavior of loggerheads. 相似文献
110.
Stefano Bianchi Giorgio Matt Fabrizio Nicastro Delphine Porquet Jacques Dubau 《Monthly notices of the Royal Astronomical Society》2005,357(2):599-607
We have calculated the equivalent widths of the absorption lines produced by Fe xxv and Fe xxvi in a Compton-thin, low-velocity photoionized material illuminated by the nuclear continuum in active galactic nuclei. The results, plotted against the ionization parameter and the column density of the gas, are a complement to those presented by Bianchi & Matt for the emission lines from the same ionic species. As an extension to the work by Bianchi & Matt, we also present a qualitative discussion on the different contributions to the He-like iron emission line complex in the regimes where recombination or resonant scattering dominates, providing a useful diagnostic tool to measure the column density of the gas. Future high-resolution missions (e.g. Astro-E2 ) will allow us to fully take advantage of these plasma diagnostics. In the meantime, we compare our results with an up-to-date list of Compton-thick and unobscured (at least at the iron line energy) Seyfert galaxies with emission and/or absorption lines from H- and He-like iron observed with Chandra and XMM–Newton . 相似文献