Contribution of interstitial OH groups to the incorporation of water in forsterite     

Etienne Balan  Marc Blanchard  Michele Lazzeri  Jannick Ingrin 《Physics and Chemistry of Minerals》2014,41(2):105-114

Water incorporation in forsterite samples synthesized under low to medium silica-activity conditions mostly occurs via a substitutional mechanism in which a Si vacancy is compensated by four protons. Corresponding IR absorption spectra display a cluster of narrow and weakly anharmonic OH-stretching bands at wavenumbers above 3,500 cm^?1. However, this diagnostic spectrum is often superimposed to one broader absorption band, rarely two, displaying pronounced temperature-dependent properties and tentatively assigned to H atoms in interstitial position (Ingrin et al. in Phys Chem Miner 40:499–510, 2013). Here, we investigate the structural and vibrational properties of selected interstitial H-bearing defects in forsterite using a first-principles modeling approach. We show that the broad bands discussed by Ingrin et al. (Phys Chem Miner 40:499–510, 2013) are most likely related to interstitial OH groups in the vacant octahedral sites alternating with the M2 sites along the c axis of the forsterite structure. The corresponding OH defects lead to the formation of fivefold coordinated Si species. Their peculiar thermal properties stem from the vibrational phase relaxation due to the anharmonic coupling of the high-energy local OH-stretching mode with a low-energy vibrational mode. This “exchange mode” corresponds to the hindered longitudinal translation of the OH group. These results suggest that at high pressure, hydrogen incorporation in forsterite is dominated by coexisting interstitial OH groups and (4H)_Si defects.  相似文献   

Analyzing spatiotemporal changes in wildfire regime and exposure across a Mediterranean fire-prone area     

Michele Salis  Alan A. Ager  Mark A. Finney  Bachisio Arca  Donatella Spano 《Natural Hazards》2014,71(3):1389-1418

We evaluated the spatiotemporal changes in wildfire regime and exposure in a fire-prone Mediterranean area (Sardinia, Italy) in relation to changes in ignition patterns, weather, suppression activities, and land uses. We also used wildfire simulations to identify fine-scale changes in wildfire exposure of important features on the island. Sardinia experienced a sharp reduction in fire number and area burned between the periods 1980–1994 and 1995–2009. Despite this decrease, losses and fatalities from wildfires continue. This suggests that localized areas and seasons of high wildfire risk persist on the island. Our analysis showed (1) a reduction in area burned (60,000–20,000 ha/year) and ignitions (3,700–2,600 fires/year), (2) an advance of 15 days for the fire season peak, (3) an increase in spring temperatures, and (4) an increase in fire exposure for WUI areas. Little change was noted for land use types and associated fuels. Most likely the reduction in fire activity may be due to a combination of social factors and suppression capabilities. On the other hand, simulation modeling suggested pockets of high wildfire exposure in specific places. The combined empirical analyses and simulation modeling provided a robust approach to understanding the spatiotemporal dynamics of wildfire risk on the island.  相似文献   

Nephelines from the Somma-Vesuvius volcanic complex (Southern Italy): crystal-chemical,structural and genetic investigations     

Giuseppina Balassone  Volker Kahlenberg  Angela Altomare  Angela Mormone  Rosanna Rizzi  Michele Saviano  Nicola Mondillo 《Mineralogy and Petrology》2014,108(1):71-90

Sixteen nephelines from different geological occurrences were sampled at the type-locality, the Somma-Vesuvius volcanic complex (southern Italy), and investigated for their chemistry and crystal structure obtained by both single-crystal and powder X-ray diffraction. Nepheline-bearing samples are metamorphic or from magmatic ejecta and pumice deposits. The lower K contents characterize the pumice- and some metamorphic-derived nephelines, whereas the higher ones are found in some samples from magmatic nodules. The amount of the anorthite molecule, quite low on average, can be more variable in the metamorphic nephelines. The crystal-structure investigations on Somma-Vesuvius samples compare well with previous studies of natural nephelines. All 16 nepheline samples adopt space group P6₃. The observed lattice parameters vary between 9.9768–9.9946 Å (for a) and 8.3614–8.3777 Å (for c), respectively. Furthermore, chemical analysis revealed that all specimens exhibit an excess of Si relative the ideal Si:Al ratio of 1:1. The analysis of the T-O distances in our samples clearly indicates a distinct ordering process of aluminium and silicon on the tetrahedral sites which is an agreement with Loewenstein’s rule. A linear correlation between the distance of symmetry equivalent split atoms O(1)-O(1)’ and the T(1)-O(1)-T(2) tilt angle was observed. The average <B-O> (B = Na) distances of all crystals are very similar which is consistent with the outcome of the site population refinement indicating full occupancy with sodium. Oriented precession-type sections of reciprocal space indicated the presence of at least the most intense family of satellite peaks, demonstrating that this group of satellite reflections can occur not only in nephelines from pegmatites and ijolites but also in rocks from completely different petrological settings.  相似文献   

A hydrogeological conceptual model of the Suio hydrothermal area (central Italy)   总被引：1，自引：0，他引：1  

Michele Saroli  Michele Lancia  Matteo Albano  Anna Casale  Gaspare Giovinco  Marco Petitta  Francesco Zarlenga  Marco dell’Isola 《Hydrogeology Journal》2017,25(6):1811-1832

A hydrogeological conceptual model has been developed that describes the hydrothermal system of Suio Terme (central Italy). The studied area is located along the peri-Tyrrhenian zone of the central Apennines, between the Mesozoic and Cenozoic carbonate platform sequences of the Aurunci Mountains and the volcanic sequences of the Roccamonfina. A multi-disciplinary approach was followed, using new hydrogeological surveys, the interpretation of stratigraphic logs of boreholes and water wells, and geophysical data—seismic sections, shear-wave velocity (Vs) crustal model and gravimetric model. The collected information allowed for construction of a conceptual hydrogeological model and characterization of the hydrothermal system. The Suio hydrothermal system is strongly influenced by the Eastern Aurunci hydrostructure. Along the southeastern side, the top of the hydrostructure sinks to ?1,000 m relative to sea level via a series of normal faults which give origin to the Garigliano graben. Geological and hydrogeological data strongly suggest the propagation and mixing of hot fluids, with cold waters coming from the shallow karst circuit. The aquitard distribution, the normal tectonic displacements and the fracturing of the karst hydrostructure strongly influence the hydrothermal basin. Carbon dioxide and other gasses play a key role in the whole circuit, facilitating the development of the hydrothermal system. The current level of knowledge suggests that the origin of the Suio hydrothermalism is the result of interaction between the carbonate reservoir of the Eastern Aurunci Mountains and the hot and deep crust of this peri-Tyrrhenian sector, where the Roccamonfina volcano represents the shallowest expression.  相似文献   

Ensuring very shallow-water sediment properties: case study from Capo Granitola harbour,Sicily (Italy)     

Michele Punzo  Giuseppe Cavuoto  Daniela Tarallo  Vincenzo Di Fiore 《Marine Geophysical Researches》2017,38(3):313-323

We present high-resolution Vp models of the Capo Granitola harbor, Sicily (Italy) obtained by first arrival traveltime tomography. Seismic data were collected along four hydrophone arrays on the sea-bottom and via a Watergun as seismic source, in order to plan dredging operations in the harbor. Using a hydrophone spacing of 2.5 m and shot spacing of 5 m, very high resolution quality data were recorded. Seismic tomography expands existing knowledge of the harbour subsoil with a penetration of about 20 m, illuminating the Lower Pleistocene bedrock (Marsala calcarenites) that corresponds to high-Vp regions (Vp?>?4.5 km/s). Low Vp (1.8–4.5 km/s) deposits belonging to terraced calcarenites (Upper Pleistocene in age) are also well imaged; they are about 8 m thick and lie below loose sand deposits (Vp?=?1.5 km/s). The substratum has an articulated morphology; Vp images unravel small steps in the basement probably related to structural discontinuities (e.g., faults). Processing data with 3D techniques enables images of the structure and the thickness of the lithotypes to be reconstructed, thus leading to large-scale, realistic estimates of the total quantity of material to be excavated or dredged. Tomographic profiles permit clear discrimination of the soft sediment above the basement and thus allow the determination of the total volume of sediment above the seismic bedrock, estimated at about 265,000 m³.  相似文献   

Model-based characterization of permeability damage control through inhibitor injection under parametric uncertainty     

Mahmudova  Ayisha  Borsi  Iacopo  Porta  Giovanni Michele 《Computational Geosciences》2022,26(5):1119-1134

Computational Geosciences - Damage in subsurface formations caused by mineral precipitation decreases the porosity and permeability, eventually reducing the production rate of wells in plants...  相似文献