H-bonding scheme and cation partitioning in axinite: a single-crystal neutron diffraction and Mössbauer spectroscopic study     

G. Diego Gatta  Günther J. Redhammer  Alessandro Guastoni  Giorgio Guastella  Martin Meven  Alessandro Pavese 《Physics and Chemistry of Minerals》2016,43(5):341-352

The crystal chemistry of a ferroaxinite from Colebrook Hill, Rosebery district, Tasmania, Australia, was investigated by electron microprobe analysis in wavelength-dispersive mode, inductively coupled plasma–atomic emission spectroscopy (ICP–AES), ⁵⁷Fe Mössbauer spectroscopy and single-crystal neutron diffraction at 293 K. The chemical formula obtained on the basis of the ICP–AES data is the following: \( ^{X1,X2} {\text{Ca}}_{4.03} \,^{Y} \left( {{\text{Mn}}_{0.42} {\text{Mg}}_{0.23} {\text{Fe}}^{2 + }_{1.39} } \right)_{\varSigma 2.04} \,^{Z1,Z2} \left( {{\text{Fe}}^{3 + }_{0.15} {\text{Al}}_{3.55} {\text{Ti}}_{0.12} } \right)_{\varSigma 3.82} \,^{T1,T2,T3,T4} \left( {{\text{Ti}}_{0.03} {\text{Si}}_{7.97} } \right)_{\varSigma 8} \,^{T5} {\text{B}}_{1.96} {\text{O}}_{30} \left( {\text{OH}} \right)_{2.18} \). The ⁵⁷Fe Mössbauer spectrum shows unambiguously the occurrence of Fe²⁺ and Fe³⁺ in octahedral coordination only, with Fe²⁺/Fe³⁺ = 9:1. The neutron structure refinement provides a structure model in general agreement with the previous experimental findings: the tetrahedral T1, T2, T3 and T4 sites are fully occupied by Si, whereas the T5 site is fully occupied by B, with no evidence of Si at the T5, or Al or Fe³⁺ at the T1–T5 sites. The structural and chemical data of this study suggest that the amount of B in ferroaxinite is that expected from the ideal stoichiometry: 2 a.p.f.u. (for 32 O). The atomic distribution among the X1, X2, Y, Z1 and Z2 sites obtained by neutron structure refinement is in good agreement with that based on the ICP–AES data. For the first time, an unambiguous localization of the H site is obtained, which forms a hydroxyl group with the oxygen atom at the O16 site as donor. The H-bonding scheme in axinite structure is now fully described: the O16–H distance (corrected for riding motion effect) is 0.991(1) Å and an asymmetric bifurcated bonding configuration occurs, with O5 and O13 as acceptors [i.e. with O16···O5 = 3.096(1) Å, H···O5 = 2.450(1) Å and O16–H···O5 = 123.9(1)°; O16···O13 = 2.777(1) Å, H···O13 = 1.914(1) Å and O16–H···O13 = 146.9(1)°].  相似文献   

An Innovative Approach to Meteorite Analysis by Laser‐Induced Breakdown Spectroscopy          下载免费PDF全文

Giorgio S. Senesi  Gioacchino Tempesta  Paola Manzari  Giovanna Agrosì 《Geostandards and Geoanalytical Research》2016,40(4):533-541

An innovative approach of double pulse laser‐induced breakdown spectroscopy (DP‐LIBS) coupled with optical microscopy was applied to the characterisation and quantitative analysis of the Agoudal iron meteorite in bulk sample and in petrographic thin section. Qualitative analysis identified the elements Ca, Co, Fe, Ga, Li and Ni in the thin section and the whole meteorite. Two different methods, calibration‐free LIBS and one‐point calibration LIBS, were used as complementary methodologies for quantitative LIBS analysis. The elemental composition data obtained by LIBS were in good agreement with the compositional analyses obtained by traditional methods generally applied for the analysis of meteorites, such as ICP‐MS and EDS‐SEM. Besides the recognised advantages of LIBS over traditional techniques, including versatility, minimal destructivity, lack of waste production, low operating costs, rapidity of analysis, availability of transportable or portable systems, etc., additional advantages of this technique in the analysis of meteorites are precision and accuracy, sensitivity to low atomic number elements such as Li and the capacity to detect and quantify Co contents that cannot be obtained by EDS‐SEM.  相似文献   

Facies and Late Triassic fossils in the Roisan zone,Austroalpine Dent Blanche and Mt Mary-Cervino nappe system,NW Alps     

Gloria Ciarapica  Leonsevero Passeri  Franco Bonetto  Giorgio Vittorio Dal Piaz 《Swiss Journal of Geoscience》2016,109(1):69-81

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The ARIEL Instrument Control Unit design     

M. Focardi  E. Pace  M. Farina  A. M. Di Giorgio  J. Colomé Ferrer  I. Ribas  C. Sierra Roig  L. Gesa Bote  J. C. Morales  J. Amiaux  C. Cara  J. L. Augurés  E. Pascale  G. Morgante  V. Da Deppo  M. Pancrazzi  V. Noce  S. Pezzuto  M. Frericks  F. Zwart  G. Bishop  K. Middleton  P. Eccleston  G. Micela  G. Tinetti 《Experimental Astronomy》2018,45(1):1-20

In this paper we present the electromagnetic modeling and beam pattern measurements of a 16-elements ultra wideband sparse random test array for the low frequency instrument of the Square Kilometer Array telescope. We discuss the importance of a small array test platform for the development of technologies and techniques towards the final telescope, highlighting the most relevant aspects of its design. We also describe the electromagnetic simulations and modeling work as well as the embedded-element and array pattern measurements using an Unmanned Aerial Vehicle system. The latter are helpful both for the validation of the models and the design as well as for the future instrumental calibration of the telescope thanks to the stable, accurate and strong radio frequency signal transmitted by the UAV. At this stage of the design, these measurements have shown a general agreement between experimental results and numerical data and have revealed the localized effect of un-calibrated cable lengths in the inner side-lobes of the array pattern.  相似文献   

Experimental models of extension of continental lithosphere weakened by percolation of asthenospheric melts     

Giacomo Corti  Marco Bonini  Fabrizio Innocenti  Piero Manetti  Giovanni B. Piccardo  Giorgio Ranalli 《Journal of Geodynamics》2007,43(4-5):465-483

Analogue models are used to investigate extension of a continental lithosphere weakened by asthenospheric melts percolating through the upper mantle, a process that has been hypothesised to control the opening of the Ligurian Tethys. Models were performed in a centrifuge apparatus and reproduced, by using materials such as sand and viscous mixtures, extension of 60-km thick, three-layer continental lithosphere floating above the asthenosphere. The percolated lithospheric mantle was assumed to be characterised by a rheological behaviour similar to that of the asthenosphere. Two sets of experiments investigated the influence on deformation of (1) the thickness of the percolated mantle and the associated strength contrast between the normal and weakened lithosphere, and (2) the lateral width of the weakened zone. Model results suggest that mantle percolation by asthenospheric melts is able to promote strong localised thinning of the continental lithosphere, provided that a significant thickness of the lithospheric mantle is weakened by migrating melts within a narrow region. Strain localisation is maximised for percolation of the whole lithospheric mantle and strong strength contrast between the normal and weakened lithosphere. Under these conditions, the thickness of the lithosphere may be reduced to less than 12 km in 3 Ma of extension. Conversely, localised thinning is strongly reduced if the thickness of the percolated zone is ≤1/3 of the thickness of the whole lithospheric mantle and/or the lithosphere is weakened over wide regions. Overall, model results support the working hypothesis that mantle percolation by asthenospheric melts is a controlling factor in the transition from distributed continental deformation to localised oceanic spreading.  相似文献   

Field study and laboratory experiments of bubble plumes in shallow seas as analogues of sub-seabed CO₂ leakages     

Stefania Espa  Giorgio Caramanna  Vanda Bouché 《Applied Geochemistry》2010

To understand the effects of increased levels of CO₂ on the marine realm, it is possible to study areas where, for natural reasons, there are emissions of CO₂ from the seabed. One of these areas is located east of Panarea Island (Aeolian Islands – Southern Tyrrhenian Sea – Italy). Here, the volcanic activity that characterizes the Aeolian archipelago causes a continuous release of CO₂ (up to 98% of the total gas) from several vents on the seafloor in shallow water. This area was studied by means of surface techniques and direct SCUBA diving surveys; the data presented refers to a field campaign performed in 2008. To collect the necessary data, some dedicated sampling and measuring techniques were developed for use in an underwater environment. The chemistry of the fluids and their influence on the water body was determined via logs and transects in the field and by gas-chromatographic and liquid-chromatographic laboratory analysis. The flux from some of the main gas vents was also measured directly underwater. Furthermore, some laboratory experiments in a two-layer stratified fluid were conducted to understand the main features of the physical interaction of a gas plume with the surrounding environment. Both field and laboratory experiments show that there is a development of a pseudo-convective cell around the rising plume with the formation of vortices that act as a physical barrier thus reducing the interaction between the plume and the surrounding water.  相似文献   

Recent Trends Towards Oligotrophication of the Northern Adriatic: Evidence from Chlorophyll <Emphasis Type="Italic">a</Emphasis> Time Series     

Patricija Mozetič  Cosimo Solidoro  Gianpiero Cossarini  Giorgio Socal  Robert Precali  Janja Francé  Franco Bianchi  Cinzia De Vittor  Nenad Smodlaka  Serena Fonda Umani 《Estuaries and Coasts》2010,33(2):362-375

The results of the updated and quality-checked data base of field observations on chlorophyll a (Chl a) collected in the period 1970–2007 in the Northern Adriatic Sea are presented. From the last decade, SeaWiFS satellite information was also considered. Results demonstrate a global tendency towards Chl a reduction in the period of investigation, which is more marked in the eutrophic area under the influence of the Po River. In the rest of the basin, which presents meso- or oligotrophic characteristics, long-term changes are more difficult to detect. The long-term field dataset can be divided into two periods: the last decade characterized by the strong decrease observed in the whole northern Adriatic and the earlier period with no or slight increase. The recent substantial reduction of Chl a concentrations is confirmed all over the basin (−0.11 mg m⁻³ year⁻¹) from satellite-derived information. Results are consistent with recently evidenced decrease in concentrations of phosphate and ammonia and point to the existence of oligotrophication in the Northern Adriatic. Results indicate forcefully that the still common perception of the Adriatic Sea as a very eutrophic basin is no longer appropriate, at least for its northern part and in recent years.  相似文献   

The role of preconditioning in the solution to FE coupled consolidation equations by Krylov subspace methods     

Massimiliano Ferronato  Giorgio Pini  Giuseppe Gambolati 《国际地质力学数值与分析法杂志》2009,33(3):405-423

The repeated solution in time of the linear system arising from the finite element integration of coupled consolidation equations is a major computational effort. This system can be written in either a symmetric or an unsymmetric form, thus calling for the implementation of different preconditioners and Krylov subspace solvers. The present paper aims at investigating when either a symmetric or an unsymmetric approach should be better used. The results from a number of representative numerical experiments indicate that a major role in selecting either form is played by the preconditioner rather than by the Krylov subspace method itself. Two other important issues addressed are the size of the time integration step and the possible lumping of the flow capacity matrix. It appears that ad hoc block constrained preconditioners provide the most robust algorithm independently of the time step size, lumping, and symmetry. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Mantle rheology: radial and lateral viscosity variations inferred from microphysical creep laws     

Giorgio Ranalli   《Journal of Geodynamics》2001,32(4-5)

Inferences on the rheology of the mantle based on theoretical and experimental rate equations for steady state creep are discussed and compared with results from geophysical models. The radial increase of viscosity by one to three orders of magnitude across the mantle, required by inversion of postglacial rebound and geodynamic data, is confirmed by microphysical models based on the estimation of continuous and discontinuous changes of creep parameters with depth. The upper mantle (viscosity 10²⁰–10²¹ Pa s) is likely to show non-Newtonian rheology (power-law creep) for average grain sizes larger than 0.1 mm as an order of magnitude. Given the variability of both grain size and stress conditions, local regions of linear rheology can be present. The rheology of transition zone and lower mantle (viscosity 10²²–10²⁴ Pa s) cannot be definitely resolved at present. Estimation of creep parameters leads to possible nonlinear or mixed rheology, if grain sizes are not lower than 0.1 mm and flow conditions can be approximated by a constant strain rate of about 10⁻¹⁵ s⁻¹. This conclusion can be modified by different flow conditions (e.g. a decrease in strain rate or constant viscous dissipation). Furthermore, experiments on fine-grained garnetites and perovskite analogues have shown that diffusion creep is predominant at laboratory conditions. However, the pressure dependence of creep in these phases is unknown, and therefore direct extrapolation to lower mantle conditions is necessarily speculative. Lateral variations of viscosity, largest in the upper and lowermost mantle (up to 2–4 orders of magnitude) are predicted by models based on lateral temperature anomalies derived from seismic tomographic models.  相似文献   

The relationship between websterite and peridotite in the Balmuccia peridotite massif (NW Italy) as revealed by trace element variations in clinopyroxene   总被引：7，自引：0，他引：7  

Rivalenti  Giorgio  Mazzucchelli  Maurizio  Vannucci  Riccardo  Hofmann  Albrecht W.  Ottolini  Luisa  Bottazzi  Piero  Obermiller  Walter 《Contributions to Mineralogy and Petrology》1995,122(3):275-288

 Field, mineralogical and petrological data are presented on a newly found carbonatite occurrence associated with “kamafugite” lava at Cupaello, central Italy. This carbonatite occurrence is part of the Late Pleistocene Umbria-Latium ultra-alkaline district (ULUD) which extends southwards within the Apennines to Mount Vulture, delineating an important magmatic province along the most peripheral belt of the Tyrrhenian extensional tectonic system. This province is distinct, but probably related genetically with the more abundant and common leucite-bearing assemblages of the Roman Comagmatic Region and represents the first reported occurrence of carbonatite assemblages in the Mediterranean Basin. The Cupaello suite indicates that primary or near-primary mantle silicate melts of “kamafugitic” composition are transitional with Ca-carbonatite liquid and provides direct evidence of immiscibility of carbonatite from “kamafugite” magma. It is inferred that a primary mantle origin of Ca-carbonatites is conditional upon a potential silicate magma that may be coupled with the carbonatite, but may not have reached the surface. The data indicate a strong genetic link between ULUD Ca-carbonatites and some African analogues, supporting the view that their genesis depends on similar source and associated tectonic conditions. Received: 17 January 1995 / Accepted: 14 June 1995  相似文献