Fluid geochemistry of natural manifestations from the Southern Poroto–Rungwe hydrothermal system (Tanzania): Preliminary conceptual model     

Manuëlla Delalande  Laurent Bergonzini  Fabrizio Gherardi  Massimo Guidi  Luc Andre  Issah Abdallah  David Williamson 《Journal of Volcanology and Geothermal Research》2011,199(1-2):127-141

The South Poroto–Rungwe geothermal field, in the northern part of the Malawi rift, Tanzania divides in two main areas. The relatively high altitude northern area around the main Ngozi, Rungwe, Tukuyu and Kyejo volcanoes, is characterised by cold and gas-rich springs. In contrast, hot springs occur in the southern and low-altitude area between the Kyela and Livingstone faults. The isotopic signature of the almost stagnant, cold springs of the Northern district is clearly influenced by H₂O–CO_2(g) exchange as evidenced from negative oxygen-shifts in the order of few deltas permil. In contrast, the isotopic signature of waters discharged from the hot springs of the Southern district is markedly less affected by the H₂O–CO_2(g) interaction. This evidence is interpreted as an effect of the large, permanent outflow of these springs, which supports the hypothesis of a regional-scale recharge of the major thermal springs. Measurements of carbon isotope variations of the dissolved inorganic carbon of waters and CO_2(g) from the Northern and Southern springs support a model of CO_2(g)-driven reactivity all over the investigated area. Our combined chemical and isotopic results show that the composition of hot springs is consistent with a mixing between (i) cold surface fresh (SFW) and (ii) Deep Hot Mineralised (DHMW) Water, indicating that the deep-originated fluids also supply most of the aqueous species dissolved in the surface waters used as local potable water. Based on geothermometric approaches, the temperature of the deep hydrothermal system has been estimated to be higher than 110 °C up to 185 °C, in agreement with the geological and thermal setting of the Malawi rift basin. Geochemical data point to (i) a major upflow zone of geothermal fluids mixed with shallow meteoric waters in the Southern part of the province, and (ii) gas absorption phenomena in the small, perched aquifers of the Northern volcanic highlands.  相似文献   

Worldwide trends in research on the San Andreas Fault System     

Fabrizio Terenzio Gizzi 《Arabian Journal of Geosciences》2015,8(12):10893-10909

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CO<Subscript>2</Subscript>-driven large mafic explosive eruptions: the Pozzolane Rosse case study from the Colli Albani Volcanic District (Italy)     

Carmela Freda  Mario Gaeta  Biagio Giaccio  Fabrizio Marra  Danilo M. Palladino  Piergiorgio Scarlato  Gianluca Sottili 《Bulletin of Volcanology》2011,73(3):241-256

Generally, the intensity and magnitude of explosive volcanic activity increase in parallel with SiO₂ content. Pyroclastic-flow-forming eruptions in the Colli Albani ultrapotassic volcanic district (Italy) represent the most striking exception on a global scale, with volumes on the order of tens of cubic kilometres and K-foiditic compositions (SiO₂ even <42 wt.%). Here, we reconstruct the pre-eruptive scenario and event dynamics of the ~456 ka Pozzolane Rosse (PR) eruption, the largest mafic explosive event of the Colli Albani district. In particular, we focus on the driving mechanisms for the unusually explosive eruption of a low-viscosity, mafic magma. Geologic, petrographic and geochemical data with mass balance calculations, supported by experimental data for Colli Albani magma compositions, provide evidence for significant ingestion of carbonate wall rocks by the Pozzolane Rosse K-foiditic magma. Moreover, the scattered occurrence of cored bombs in Pozzolane Rosse pyroclastic-flow deposits records carbonate entrainment even at the eruptive time scale, as also tested quantitatively by thermal modelling of magma–carbonate interaction and carbonate assimilation experiments. We suggest that the addition of free CO₂ from decarbonation of country rocks was the major factor controlling magma explosivity. High CO₂ activity in the volatile component, coupled with magma depressurisation, produced extensive leucite crystallisation at short time scales, resulting in a dramatic increase in magma viscosity and volatile pressurisation, which was manifested a change of eruptive dynamics from early effusion to the Pozzolane Rosse's highly explosive eruption climax.  相似文献   

Extrusion vs. accretion at the frictional–viscous décollement transition in experimental thrust wedges: the role of convergence velocity     

María Lujn  Fabrizio Storti  Federico Rossetti  Ana Crespo‐Blanc 《地学学报》2006,18(4):241-247

In many cases, thrust wedges accreted at shallow crustal levels show an across‐strike rheological variability along the basal décollement, notably from brittle to ductile behaviour. In this paper, we illustrate the results of sandbox analogue modelling research devoted to studying the influence of convergence velocity on wedge architecture when laterally juxtaposed frictional and viscous materials occur along the basal décollement of accreting thrust wedges. Our results show that slow convergence favours a near symmetrical distribution of thrust vergence within wedge sectors accreted above viscous décollement material, whereas fast convergence favours vergence asymmetry. In particular, at fast convergence rates the hinterlandward extrusion of viscous décollement material at the toe of the frictional wedge is favoured and contributed to accommodate a significant amount of the total contraction. Terra Nova, 18, 241–247, 2006  相似文献   

The Cosmic Foreground Explorer (COFE): A balloon-borne microwave polarimeter to characterize polarized foregrounds     

Rodrigo Leonardi  Brian Williams  Marco Bersanelli  Ivan Ferreira  Philip M. Lubin  Peter R. Meinhold  Hugh O&#x;Neill  Nathan C. Stebor  Fabrizio Villa  Thyrso Villela  Carlos A. Wuensche 《New Astronomy Reviews》2006,50(11-12):977

The COsmic Foreground Explorer (COFE) is a balloon-borne microwave polarimeter designed to measure the low-frequency and low-ℓ characteristics of dominant diffuse polarized foregrounds. Short duration balloon flights from the Northern and Southern Hemispheres will allow the telescope to cover up to 80% of the sky with an expected sensitivity per pixel better than 100 μK/deg² from 10 GHz to 20 GHz. This is an important effort toward characterizing the polarized foregrounds for future CMB experiments, in particular the ones that aim to detect primordial gravity wave signatures in the CMB polarization angular power spectrum.  相似文献   

Fault‐bend folding as an end‐member solution of (double‐edge) fault‐propagation folding     

Stefano Tavani  Fabrizio Storti 《地学学报》2006,18(4):270-275

Fault‐bend folding is the most commonly used kinematic mechanism to interpret the architecture and evolution of thrust‐related anticlines in thrust wedges. However, its basic requirement of an instantaneous propagation of the entire fault before hangingwall deformation, limits its kinematic effectiveness. To overcome this limitation, we used the interdependence between fold shape and fault slip vs. propagation rate (S/P ratio) implemented in double‐edge fault‐propagation folding. We show that very small S/P values produce fault‐propagation anticlines that, when transported forelandward along an upper décollement layer, closely resemble fault‐bend anticlines. Accordingly, if small geometric discrepancies between the two solutions are accepted, transported double‐edge fault‐propagation provides an effective kinematic alternative to fault‐bend folding. Even at very low S/P values, it in fact predicts a fast but finite propagation rate of the fault. We thus propose that double‐edge fault‐propagation folding provides a broadly applicable model of fault‐related folding that includes fault‐bend folding as an end‐member kinematic solution. Terra Nova, 18, 270–275, 2006  相似文献   

Dynamics of mineral crystallization from precipitated slab-derived fluid phase: first in situ synchrotron X-ray measurements     

Nadia Malaspina  Matteo Alvaro  Marcello Campione  Heribert Wilhelm  Fabrizio Nestola 《Contributions to Mineralogy and Petrology》2015,169(3):1-12

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Multi-methodological investigation of kunzite, hiddenite, alexandrite, elbaite and topaz, based on laser-induced breakdown spectroscopy and conventional analytical techniques for supporting mineralogical characterization     

Manuela Rossi  Marcella Dell’Aglio  Alessandro De Giacomo  Rosalba Gaudiuso  Giorgio Saverio Senesi  Olga De Pascale  Francesco Capitelli  Fabrizio Nestola  Maria Rosaria Ghiara 《Physics and Chemistry of Minerals》2014,41(2):127-140

Gem-quality alexandrite, hiddenite and kunzite, elbaite and topaz minerals were characterized through a multi-methodological investigation based on EMPA-WDS, LA-ICP-MS, and laser-induced breakdown spectroscopy (LIBS). With respect to the others, the latter technique enables a simultaneous multi-elemental composition without any sample preparation and the detection of light elements, such as Li, Be and B. The criteria for the choice of minerals were: (a) the presence of chromophore elements in minor contents and/or as traces; (b) the presence of light lithophile elements (Li, Be and B); (c) different crystal chemistry complexity. The results show that LIBS can be employed in mineralogical studies for the identification and characterization of minerals, and as a fast screening method to determine the chemical composition, including the chromophore and light lithophile elements.  相似文献   

Vestan lithologies mapped by the visual and infrared spectrometer on Dawn     

Eleonora Ammannito  M. Cristina De Sanctis  Fabrizio Capaccioni  M. Teresa Capria  F. Carraro  Jean‐Philippe Combe  Sergio Fonte  Alessandro Frigeri  Steven P. Joy  Andrea Longobardo  Gianfranco Magni  Simone Marchi  Thomas B. McCord  Lucy A. McFadden  Harry Y. McSween  Ernesto Palomba  Carle M. Pieters  Carol A. Polanskey  Carol A. Raymond  Jessica M. Sunshine  Federico Tosi  Francesca Zambon  Christopher T. Russell 《Meteoritics & planetary science》2013,48(11):2185-2198

We present global lithological maps of the Vestan surface based on Dawn mission's Visible InfraRed (VIR) Spectrometer acquisitions with a spatial sampling of 200 m. The maps confirm the results obtained with the data set acquired by VIR with a spatial sampling of 700 m, that the reflectance spectra of Vesta's surface are dominated by pyroxene absorptions that can be interpreted within the context of the distribution of howardites, eucrites, and diogenites (HEDs). The maps also partially agree with the ground and Hubble Space Telescope observations: they confirm the background surface being an assemblage of howardite or polymict eucrite, as well as the location of a diogenitic‐rich spot; however, there is no evidence of extended olivine‐rich regions in the equatorial latitudes. Diogenite is revealed on the Rheasilvia basin floor, indicating that material of the lower crust/mantle was exposed. VIR also detected diogenites along the scarp of Matronalia Rupes, and the rims of Severina and a nearby, unnamed crater, and as ejecta of Antonia crater. The diogenite distribution is fully consistent with petrological constraints; although the mapped distribution does not provide unambiguous constraints, it favors the hypothesis of a magma ocean.  相似文献   

New thermoelastic parameters of natural <Emphasis Type="Italic">C</Emphasis>2/<Emphasis Type="Italic">c</Emphasis> omphacite     

Francesco?PandolfoEmail author  Fabrizio?Nestola  Fernando?Cámara  M.?Chiara?Domeneghetti 《Physics and Chemistry of Minerals》2012,39(4):295-304

The compressibility at room temperature and the thermal expansion at room pressure of two disordered crystals (space group C2/c) obtained by annealing a natural omphacite sample (space group P2/n) of composition close to Jd₅₆Di₄₄ and Jd₅₅Di₄₅, respectively, have been studied by single-crystal X-ray diffraction. Using a Birch–Murnaghan equation of state truncated at the third order [BM3-EoS], we have obtained the following coefficients: V ₀ = 421.04(7) Å³, K _T0 = 119(2) GPa, K′ = 5.7(6). A parameterized form of the BM3 EoS was used to determine the axial moduli of a, b and c. The anisotropy scheme is β _c  ≤ β _a  ≤ β _b , with an anisotropy ratio 1.05:1.00:1.07. A fitting of the lattice variation as a function of temperature, allowing for linear dependency of the thermal expansion coefficient on the temperature, yielded α_V(1bar,303K) = 2.64(2) × 10⁻⁵ K⁻¹ and an axial thermal expansion anisotropy of α _b  ≫ α _a  > α _c . Comparison of our results with available data on compressibility and thermal expansion shows that while a reasonable ideal behaviour can be proposed for the compressibility of clinopyroxenes in the jadeite–diopside binary join [K _T0 as a function of Jd molar %: K _T0 = 106(1) GPa + 0.28(2) × Jd_(mol%)], the available data have not sufficient quality to extract the behaviour of thermal expansion for the same binary join in terms of composition.  相似文献