The role of syn-eruptive vesiculation on explosive basaltic activity at Mt. Etna,Italy     

Margherita Polacci  Michael R. Burton  Alessandro La Spina  Filippo Murè  Stefano Favretto  Franco Zanini 《Journal of Volcanology and Geothermal Research》2009,179(3-4):265-269

We investigated the dynamics of explosive activity at Mt. Etna between 31 August and 15 December 2006 by combining vesicle studies in the erupted products with measurements of the gas composition at the active, summit crater. The analysed scoria clasts present large, connected vesicles with complex shapes and smaller, isolated, spherical vesicles, the content of which increases in scoriae from the most explosive events. Gas geochemistry reports CO₂/SO₂ and SO₂/HCl ratios supporting a deep-derived gas phase for fire-fountain activity. By integrating results from scoria vesiculation and gas analysis we find that the highest energy episodes of Mt. Etna activity in 2006 were driven by a previously accumulated CO₂-rich gas phase but we highlight the lesser role of syn-eruptive vesicle nucleation driven by water exsolution during ascent. We conclude that syn-eruptive vesiculation is a common process in Etnean magmas that may promote a deeper conduit magma fragmentation and increase ash formation.  相似文献   

Numerical comparison of different convergent plate contacts: subduction channel and subduction fault   总被引：2，自引：0，他引：2  

Roberta De Franco  Rob Govers  Rinus Wortel 《Geophysical Journal International》2007,171(1):435-450

At convergent plate boundaries, the properties of the actual plate contact are important for the overall dynamics. Convergent plate boundaries both mechanically decouple and link tectonic plates and accommodate large amounts of strain. We investigate two fundamental physical states of the subduction contact: one based on a fault and the other based on a subduction channel. Using a finite element method, we determine the specific signatures of both states of the subduction contact. We pay particular attention to the overriding plate. In a tectonic setting of converging plates, where the subducting plate is freely moving, the subduction channel reduces compression relative to the fault model. In a land-locked basin setting, where the relative motion between the far field of the plates is zero, the subduction channel model produces tensile stress regime in the overriding plate, even though the amount of slab roll-back is small. The fault model shows a stronger development of slab roll-back and a compressive stress regime in the upper plate. Based on a consistent comparison of fault and channel numerical models, we find that the nature of the plate contact is one of the controlling factors in developing or not of backarc extension. We conclude that, the type of plate contact plays a decisive role in controlling the backarc state of stress. To obtain backarc extension, roll-back is required as an underling geodynamic process, but it is not always a sufficient condition.  相似文献   

Application of the FAO quantitative and SINDI methods to assess the quality of different soils in Castilla-La Mancha (Spain)     

V. González-Quiñones  A. de la Torre  M. P. García  A. Polo  R. Jiménez-Ballesta 《Environmental Geology》2007,53(3):527-531

In the region of Castilla-La Mancha (Spain), over half of the soils are under cropping. This vast agricultural activity, combined with other anthropological uses, has led to a deterioration of the soil quality and virtual degradation. Therefore, it was deemed to assess the quality of these soils, which was achieved by applying two different methods. Three soils, representative of typical conditions in this community, were sampled and diverse properties were analysed in order to apply two different approaches. The first soil evaluation was carried out by a traditional method developed by FAO using a productivity index, whereas the second method consisted of the application of a new method called SINDI, developed in New Zealand. Both approaches make an evaluation based on a number of indicators that differs in each case. These differences explain why each method ranked the soils studied in different order reaching diverse conclusions on their quality.  相似文献   

Geodynamic settings and tectonic model of skarn gold deposits in China: An overview   总被引：47，自引：0，他引：47  

Yan-Jing Chen  Hua-Yong Chen  Khin Zaw  Franco Pirajno  Zeng-Jie Zhang 《Ore Geology Reviews》2007,31(1-4):139-169

Seventy skarn-type gold deposits, including 1 super-large, 19 large and 24 medium-sized, are known from different geotectonic units of China. They contain a total resource of approximately 1000 t of gold (625 t in South China), and account for 20% of China's gold reserves. These skarn deposits are sited in collisional orogenic belts, fault-controlled magmatic belts and reactivated cratonic margins. All of the Chinese skarn gold provinces were affected by Phanerozoic collisional orogenesis. The timing of the metallogenic events and the spatial–temporal distribution of the Chinese skarn gold deposits indicates that they were formed during ore-forming processes linked to the transition from shortening to extension in the geodynamic evolution of a collision orogen, and not to subduction systems as is commonly advocated for porphyry copper systems around the Pacific Rim.  相似文献   

Application of <Emphasis Type="Italic">fuzzy logic and data mining</Emphasis> techniques as tools for qualitative interpretation of acid mine drainage processes     

J. Aroba  J. A. Grande  J. M. Andújar  M. L. de la Torre  J. C. Riquelme 《Environmental Geology》2007,53(1):135-145

In this article, a set of clustering algorithms based on Fuzzy Logic and Data Mining are applied, allowing to obtain data in the form of linguistic rules and charts about the behaviour of the Tinto and Odiel river estuary (SW Spain) affected by Acid Mine Drainage (AMD). In order to provide researchers with no skills on data mining techniques an easy and intuitive interpretation, we have developed a computer tool based on fuzzy logic that allows immediate qualitative analysis of the data contained in a data from the estuary water chemical analyses, and serves as a contrast to functioning models previously proposed with classical statistics.  相似文献   

Geological and geochemical characteristics of the Baimazhai Ni-Cu-（PGE） sulphide deposit in Yunnan, China     

PU Chuanjie QIN Dexian NIAN Hong ZHANG Xueshu Franco PIRAJNO FAN Zhuguo 《中国地球化学学报》2007,26(4):374-383

The sulphide ores of the Baimazhai deposit, although typically orthomagmatic, locally exhibit peculiar textural features and are intimately associated with hydrothermal minerals, such as biotite, amphibole and chlorite. This association suggests that the magmatic sulphide ores were subjected to hydrothermal alteration and subsequent redistribution, resulting in the observed textural features. Geochemically, the Baimazhai sulphide ores are enriched in Cu, Pd and Au, which,according to previous studies, reflects the action of hydrothermal fluids. Interestingly, Ar-Ar dating yielded the plateau ages of about 160–170 Ma, which are at odds with the established Permian age of the Emeishan large igneous province. We interpreted these younger ages as due to thermal resetting during post-Permian tectonothermal events. We have proposed a model in which tectonic movements and hydrothermal fluids related to these events modified the pre-existing magmatic sulphides. Given the degree of overprint, we suggested two possible scenarios: 1) the sulphide disseminations that surround the massive magmatic ores are the result of deformation and hydrothermal alteration; and 2) there were both magmatic massive and disseminated sulphides, in which case the scale and relocation of remobilization would have been smaller, but still detectable.  相似文献   

Thermal springs,fumaroles and gas vents of continental Yemen: Their relation with active tectonics,regional hydrology and the country’s geothermal potential     

Angelo Minissale  Mohamed A. Mattash  Orlando Vaselli  Franco Tassi  Ismail N. Al-Ganad  Enrico Selmo  Nasr M. Shawki  Dario Tedesco  Robert Poreda  Abdassalam M. Ad-Dukhain  Mohammad K. Hazzae 《Applied Geochemistry》2007

Most thermal springs of continental Yemen (about 65 emergences at 48 sampling sites) and a couple of fumaroles and boiling water pools have been sampled and analyzed for chemical and isotopic composition in the liquid phase and the associated free-gas phase. Whatever the emergence, all the water discharges have an isotopic signature of meteoric origin. Springs seeping out from high altitudes in the central volcanic plateau show a prevalent Na–HCO₃-composition, clearly affected by an anomalous flux of deep CO₂ deriving from active hydrothermal systems located in the Jurassic Amran Group limestone sequence and/or the Cretaceous Tawilah Group, likely underlying the 2000–3000 m thick volcanic suite. At lower elevations, CO₂ also affects the composition of some springs emerging at the borders of the central volcanic plateau.  相似文献   

An earthquake scenario for the microzonation of Sofia and the vulnerability of structures designed by use of the Eurocodes   总被引：3，自引：0，他引：3  

Paskaleva Ivanka  Dimova Silvia  G.F. Panza Giuliano  Vaccari Franco   《Soil Dynamics and Earthquake Engineering》2007,27(11):1028-1041

The study of the site effects and the microzonation of a part of the metropolitan Sofia, based on the modelling of seismic ground motion along three cross-sections are performed. Realistic synthetic strong motion waveforms are computed for scenario earthquakes (M=7) applying a hybrid modelling method, based on the modal summation technique and finite differences scheme. The synthesized ground motion time histories are source and site specific. The site amplification is determined in terms of response spectra ratio (RSR). A suite of time histories and quantities of earthquake engineering interest are provided. The results of this study constitute a “database” that describes the ground shaking of the urban area. A case study of experiment-based assessment of vulnerability of a cast-in-situ single storey, industrial, reinforced concrete frame, designed according to Eurocodes 2 and 8 is presented. The main characteristics of damage index and storey drift are discussed for the purposes of microzonation.  相似文献   

The global distribution of gravity wave energy in the lower stratosphere derived from GPS data and gravity wave modelling: Attempt and challenges     

K. Frhlich  T. Schmidt  M. Ern  P. Preusse  A. de la Torre  J. Wickert  Ch. Jacobi 《Journal of Atmospheric and Solar》2007,69(17-18):2238

Five years of global temperatures retrieved from radio occultations measured by Champ (Challenging Minisatellite Payload) and SAC-C (Satelite de Aplicaciones Cientificas-C) are analyzed for gravity waves (GWs). In order to separate GWs from other atmospheric variations, a high-pass filter was applied on the vertical profile. Resulting temperature fluctuations correspond to vertical wavelengths between 400 m (instrumental resolution) and 10 km (limit of the high-pass filter). The temperature fluctuations can be converted into GW potential energy, but for comparison with parameterization schemes GW momentum flux is required. We therefore used representative values for the vertical and horizontal wavelength to infer GW momentum flux from the GPS measurements. The vertical wavelength value is determined by high-pass filtering, the horizontal wavelength is adopted from a latitude-dependent climatology. The obtained momentum flux distributions agree well, both in global distribution and in absolute values, with simulations using the Warner and McIntyre parameterization (WM) scheme. However, discrepancies are found in the annual cycle. Online simulations, implementing the WM scheme in the mechanistic COMMA-LIM (Cologne Model of the Middle Atmosphere—Leipzig Institute for Meteorology) general circulation model (GCM), do not converge, demonstrating that a good representation of GWs in a GCM requires both a realistic launch distribution and an adequate representation of GW breaking and momentum transfer.  相似文献   

On core-collapse supernovae in normal and in Seyfert galaxies     

A.Bressan  M.Della Valle  P.Marziani 《Monthly notices of the Royal Astronomical Society》2002,331(3):L25-L29

This paper estimates the relative frequency of different types of core-collapse supernovae, in terms of the ratio between the number of Type Ib–Ic and of Type II supernovae. We estimate independently for all normal and Seyfert galaxies whose radial velocity is ≤14 000 km s⁻¹, and which had at least one supernova event recorded in the Asiago catalogue from 1986 January to 2000 August. We find that the ratio is  ≈0.23±0.05  in normal galaxies. This value is consistent with constant star formation rate and with a Salpeter initial mass function and an average binary rate ≈50 per cent. On the contrary, Seyfert galaxies exceed the ratio in normal galaxies by a factor ≈4 at a confidence level ≳2 σ . A caveat is that the numbers for Seyferts are still small (six of Type Ib–Ic and six of Type II supernovae discovered as yet). Assumed to be real, this excess of Type Ib/c supernovae may indicate a burst of low-age star formation  ( τ ≲20 Myr)  , a high incidence of binary systems in the inner regions  ( r ≲0.4 R ₂₅)  of Seyfert galaxies, or a top-loaded mass function.  相似文献