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31.
Francesco Di Benedetto Francesco D’Acapito Gabriele Fornaciai Massimo Innocenti Giordano Montegrossi Luca A. Pardi Silvia Tesi Maurizio Romanelli 《Physics and Chemistry of Minerals》2010,37(5):283-289
An X-ray absorption spectroscopy (XAS) study of the Fe local environment in natural amethyst (a variety of α-quartz, SiO2) has been carried out. Room temperature measurements were performed at the Fe K-edge (7,112 eV), at both the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions. Experimental results were then compared with DFT calculations. XANES experimental spectra suggest Fe to occur mainly in the trivalent state, although a fraction of Fe2+ is identified. EXAFS spectra, on the other hand, reveal an unusual short distance for the first coordination shell: = 1.78(2) Å, the coordination number being 2.7(5). These results allow to establish that Fe replaces Si in its tetrahedral site, and that numerous local distortions are occurring as a consequence of the presence of Fe3+ variably compensated by protons and/or alkaline ions, or uncompensated. The formal valence of Fe, on the basis of both experimental and DFT structural features, can be either 4+ or 3+. Taking into account the XANES evidences, we suggest that Fe mainly occurs in the trivalent state, compensated by protons, and that a minor fraction of Fe4+ is stabilised by the favourable local structural arrangement. 相似文献
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Jérôme Gattacceca Francis M. McCubbin Jeffrey N. Grossman Devin L. Schrader Nancy L. Chabot Massimo D'Orazio Cyrena Goodrich Ansgar Greshake Juliane Gross Katherine Helen Joy Mutsumi Komatsu Bingkui Miao 《Meteoritics & planetary science》2023,58(6):901-904
Meteoritical Bulletin 111 contains the 3094 meteorites approved by the Nomenclature Committee of the Meteoritical Society in 2022. It includes 11 falls (Antonin, Botohilitano, Cranfield, Golden, Great Salt Lake, Longde, Msied, Ponggo, Qiquanhu, Tiglit, Traspena), with 2533 ordinary chondrites, 165 HED, 123 carbonaceous chondrites (including 4 ungrouped), 82 lunar meteorites, 28 Rumuruti chondrites, 27 iron meteorites, 23 ureilites, 22 mesosiderites, 22 Martian meteorites, 21 primitive achondrites (one ungrouped), 17 ungrouped achondrites, 13 pallasites, 7 enstatite achondrites, 6 enstatite chondrites, and 5 angrites. Of the meteorites classified in 2022, 1787 were from Antarctica, 1078 from Africa, 180 from South America, 34 from Asia, 6 from North America, 4 from Europe, and 1 from Oceania. 相似文献
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Silvia Ceramicola Daniel Praeg Andrea Cova Daniela Accettella Massimo Zecchin 《Geo-Marine Letters》2014,34(2-3):111-129
Mud volcanoes (MVs) are abundant along the eastern Mediterranean subduction zones, recording mud breccia extrusion over long timescales (106 years), but to date relatively few have been recognised in the northern Ionian Sea on the Calabrian accretionary prism (CAP). In the present study, the seafloor distribution and recent activity of MVs is investigated across a 35,600 km2 sector of the CAP using a regional acoustic dataset (multibeam bathymetric and backscatter imagery, integrated with subbottom profiles) locally ground-truthed by sediment cores. A total of 54 MVs are identified across water depths of 150–2,750 m using up to four geophysical criteria: distinctive morphology, high backscatter, unstratified subbottom facies and, in one case, a hydroacoustic flare. Fourteen MVs are identified from 3–4 criteria, of which five have been previously proven by cores containing mud breccia beneath up to 1.6 m of hemipelagic sediments (Madonna dello Ionio MVs 1–3, Pythagoras MV and the newly named Sartori MV), while nine others are identified for the first time (Athena, Catanzaro, Cerere, Diana, Giunone, Minerva, ‘right foot’, Venere 1 and 2). Forty other as yet unnamed MVs are inferred from 1–2 geophysical criteria (three from distinctive morphology alone). All but one possible MV lie on the inner plateau of the CAP, landwards of the Calabrian Escarpment in a zone up to 120 km wide that includes the inner pre-Messinian wedge and the fore-arc basins, where they are interpreted to record the ascent from depth of overpressured fluids that interacted with tectonic structures and with evaporitic or shale seals within the fore-arc basins. The rise of fluids may have been triggered by post-Messinian out-of-sequence tectonism that affected the entire pre-Messinian prism, but Plio-Quaternary sedimentation rates and depositional styles support the inference that significant mud volcanism has taken place only on the inner plateau. Sedimentation rates across the CAP applied to a 12 khz sonar detection depth of 225 cm imply that all MVs with backscatter signatures (50 of 54) have erupted mud breccias within the last 56 ka, and within the last 12.5 ka in the fore-arc basins. Ages of eruption estimated from the depth of cored mud breccias at five MVs, and a seismo-stratigraphic relationship at a sixth, indicate episodes at the last glacial maximum ca. 20 ka BP and during the postglacial period. Eruptive episodes within the Calabrian MV province constitute recurrent geohazards, separated by longer periods of quiescent (subdued) fluid seepage that are likely to support gas hydrate formation and chemosynthetic ecosystems. 相似文献
34.
Tunnelling and Hydrogeological Issues: A Short Review of the Current State of the Art 总被引:1,自引:1,他引:0
Since the 1960s, there has been an increasing interest in the understanding of the hydraulic flow inside a hard rock mass, since water inflow into deep tunnels constitute a hazard, in addition to being an important factor in controlling the advancement of excavation. The characterisation of fluid flow through hard rock masses is still one of the most challenging problems faced by geologists and engineers. A rock mass is characterised by networks of discrete and ubiquitous discontinuities that strongly affect its hydraulic properties, but detailed knowledge of the discontinuity properties allows for the evaluation of the hydraulic flow in the rock mass affected by the excavation of a tunnel. A geostructural field survey is fundamental in order to correctly define the discontinuity types, settings and networks. Numerous approaches have been proposed to estimate the water inflow based on empirical relations supported by field experience and case studies, as well as analytical solutions. Often, however, these approaches are not easily applicable in standard practice and in complex scenarios. The most appropriate approach to characterising the hydraulic flow of the rock mass and to predicting in the most effective way the expected water inflow during the excavation of a tunnel is based on a detailed geological model and geostructural analysis as described in this paper. 相似文献
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36.
Maurizio Gemelli Massimo D'Orazio Luigi Folco 《Geostandards and Geoanalytical Research》2015,39(1):55-69
We evaluate the performance of a hand‐held XRF (HHXRF) spectrometer for the bulk analysis of iron meteorites. Analytical precision and accuracy were tested on metal alloy certified reference materials and iron meteorites of known chemical composition. With minimal sample preparation (i.e., flat or roughly polished surfaces) HHXRF allowed the precise and accurate determination of most elements heavier than Mg, with concentrations > 0.01% m/m in metal alloy CRMs, and of major elements Fe and Ni and minor elements Co, P and S (generally ranging from 0.1 to 1% m/m) in iron meteorites. In addition, multiple HHXRF spot analyses could be used to determine the bulk chemical composition of iron meteorites, which are often characterised by sulfide and phosphide accessory minerals. In particular, it was possible to estimate the P and S bulk contents, which are of critical importance for the petrogenesis and evolution of Fe‐Ni‐rich liquids and iron meteorites. This study thus validates HHXRF as a valuable tool for use in meteoritics, allowing the rapid, non‐destructive (a) identification of the extraterrestrial origin of metallic objects (i.e., archaeological artefacts); (b) preliminary chemical classification of iron meteorites; (c) identification of mislabelled/unlabelled specimens in museums and private collections and (d) bulk analysis of iron meteorites. 相似文献
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40.
Fernando Cámara Gianluca Iezzi Massimo Tiepolo Roberta Oberti 《Physics and Chemistry of Minerals》2006,33(7):475-483
Lithian ferrian enstatite with Li2O = 1.39 wt% and Fe2O3 7.54 wt% was synthesised in the (MgO–Li2O–FeO–SiO2–H2O) system at P = 0.3 GPa, T = 1,000°C, fO2 = +2 Pbca, and a = 18.2113(7), b = 8.8172(3), c = 5.2050(2) Å, V = 835.79(9) Å3. The composition of the orthopyroxene was determined combining EMP, LA-ICP-MS and single-crystal XRD analysis, yielding the unit formula M2(Mg0.59Fe 0.21 2+ Li0.20) M1(Mg0.74Fe 0.20 3+ Fe 0.06 2+ ) Si2O6. Structure refinements done on crystals obtained from synthesis runs with variable Mg-content show that the orthopyroxene is virtually constant in composition and hence in structure, whereas coexisting clinopyroxenes occurring both as individual grains or thin rims around the orthopyroxene crystals have variable amounts of Li, Fe3+ and Mg contents. Structure refinement shows that Li is ordered at the M2 site and Fe3+ is ordered at the M1 site of the orthopyroxene, whereas Mg (and Fe2+) distributes over both octahedral sites. The main geometrical variations observed for Li-rich samples are actually due to the presence of Fe3+, which affects significantly the geometry of the M1 site; changes in the geometry of the M2 site due to the lower coordination of Li are likely to affect both the degree and the kinetics of the non-convergent Fe2+-Mg ordering process in octahedral sites. 相似文献