Seismic signals in geothermal areas of active volcanism: a case study from ‘La Fossa’, Vulcano (Italy)     

Antonio Montalto 《Bulletin of Volcanology》1994,56(3):220-227

Since the last eruption (1888–1890) volcanism at Vulcano, Aeolian Archipelago, southern Tyrrhenian Sea, has taken the form of persistent fumarolic activity. The gas-vapour phases of the geothermal systems are mainly discharged within two restricted areas about 1 km apart from each other, in the northern part of the island. These areas are La Fossa crater, and the beach fumaroles of the Baia di Levante. Fluids released at the two main fumarolic fields display quite different chemical and temperature characteristics, implying different origins. The local seismicity essentially takes the form of discrete shocks of shallow origin (depth1 km) at La Fossa, usually with energy < 10¹³ ergs. They are thought to be related to the uprise of pressurized hot gases and vapours discharged at the crater fumaroles. The present investigation points to the existence of two principal categories of seismic events (called M-shocks and N-shocks). These are short events (normally < 10 s). M-type shocks are thought to be due to resonance vibrations within the interior of the volcano, probably driven by the excitation of shock-waves within cavities deeply affected by deposition and alteration of self-sealant hydrothermal minerals. N-type events display features that resemble those of volcano-tectonic earthquakes, but have no recognizable S-phases. Here they are tentatively attributed to microfracturing of rocks which have been extensively hydrothermally altered. Results of the present study permit a preliminary conceptual model of the local shallow seismic processes in the framework of geochemical modelling of fumarolic activity and geological inferences from geothermal drilling.  相似文献   

Evidence of magmatic CO2-rich fluids in peraluminous graphite-bearing leucogranites from Deep Freeze Range (northern Victoria Land,Antarctica)     

Maria Luce Frezzotti  Gianfranco Di Vincenzo  Claudio Ghezzo  Ernst A. J. Burke 《Contributions to Mineralogy and Petrology》1994,117(2):111-123

Fine-grained peraluminous synkinematic leuco-monzogranites (SKG), of Cambro-Ordovician age, occur as veins and sills (up to 20–30 m thick) in the Deep Freeze Range, within the medium to high-grade metamorphics of the Wilson Terrane. Secondary fibrolite + graphite intergrowths occur in feldspars and subordinately in quartz. Four main solid and fluid inclusion populations are observed: primary mixed CO₂+H₂O inclusions + Al₂SiO₅ ± brines in garnet (type 1); early CO₂-rich inclusions (± brines) in quartz (type 2); early CO₂+CH₄ (up to 4 mol%)±H₂O inclusions + graphite + fibrolite in quartz (type 3); late CH₄+CO₂+N₂ inclusions and H₂O inclusions in quartz (type 4). Densities of type 1 inclusions are consistent with the crystallization conditions of SKG (750°C and 3 kbar). The other types are post-magmatic: densities of type 2 and 3 inclusions suggest isobaric cooling at high temperature (700–550°C). Type 4 inclusions were trapped below 500°C. The SKG crystallized from a magma that was at some stage vapour-saturated; fluids were CO₂-rich, possibly with immiscible brines. CO₂-rich fluids (±brines) characterize the transition from magmatic to post-magmatic stages; progressive isobaric cooling (T<670°C) led to a continuous decrease off _{O 2} can entering in the graphite stability field; at the same time, the feldspars reacted with CO₂-rich fluids to give secondary fibrolite + graphite. Decrease ofT andf _{O 2} can explain the progressive variation in the fluid composition from CO₂-rich to CH₄ and water dominated in a closed system (in situ evolution). The presence of N₂ the late stages indicates interaction with external metamorphic fluids.Contribution within the network Hydrothermal/metamorphic water-rock interactions in crystalline rocks: a multidisciplinary approach on paleofluid analysis. CEC program: Human Capital and Mobility  相似文献   

An observational study of coronal hole rotation over the sunspot cycle     

Patricia Navarro-Peralta  Antonio Sanchez-Ibarra 《Solar physics》1994,153(1-2):169-178

An analysis of the rotation of coronal holes (CHs) spanning 18 years was done based on data from theCatalogue of Coronal Holes (Sanchez-Ibarra and Barraza-Paredes, 1992). A differential rotation of CHs is confirmed for the totality of CHs, but a different behavior was found when those were separated as equatorial or isolated, and polar hole extensions, such as in theCatalogue. Isolated CHs show a typical differential rotation, but polar hole extensions display two different types of behavior: a rotation rate below 40° ± 5° of heliographic latitude, increasing to the equator, and a rotation rate above the same heliographic latitude but increasing to the poles. Also discussed here is how this last result agrees with other studies that indicate the mostly rigid rotation of the corona at higher latitudes.  相似文献   

Far-infrared observations of main sequence stars surrounded by dust shells     

P. M. Harvey  B. Smith  J. Di Francesco 《Astrophysics and Space Science》1995,224(1-2):475-476

We present 50 and 100µm photometry and size information for several main sequence stars surrounded by dust shells. The observations from NASA's Kuiper Airborne Observatory include the Vega-like stars, Beta Pic, Fomalhaut, as well as four stars suggested by Walker and Wolstencroft to belong possibly to the same class. The results of our observations are best interpreted as upper limits to the far-infrared sizes of the dust clouds around all of the stars except Fomalhaut and Beta Pic. We have also fit simple, optically thin models to the Beta Pic data to explore the range of shell parameters consistent with our limits and with previous observations.  相似文献   

Observation of MKN 501 at gamma-ray energies     

L. Bassani  R. C. Butler  A. J. Dean  G. Di Cocco  A. Della Ventura  F. Perotti  G. Villa 《Astrophysics and Space Science》1982,82(2):311-316

During a balloon flight in September 1979 of the MISO low-energy -ray telescope, the BL Lac-object MkN 501 was studied in the hard X-ray range above 30 keV and in the low energy -ray range up to 19 MeV. No statistically significant X- and -ray fluxes were detected. The implications of the upper limits obtained are discussed in the light of the relativistic jet theories recently proposed.  相似文献   

On Szebehely's problem for holonomic systems involving generalized potential functions     

Francesco Borghero  Antonio Melis 《Celestial Mechanics and Dynamical Astronomy》1990,49(3):273-284

We consider the problem of finding the generalized potential function V = U _i(q ¹, q ²,..., q ⁿ)q ⁱ + U(q ¹, q ²,...;q ⁿ) compatible with prescribed dynamical trajectories of a holonomic system. We obtain conditions necessary for the existence of solutions to the problem: these can be cast into a system of n – 1 first order nonlinear partial differential equations in the unknown functions U ₁, U ₂,...;, U _n, U. In particular we study dynamical systems with two degrees of freedom. Using adapted coordinates on the configuration manifold M ₂ we obtain, for potential function U(q ¹, q ²), a classic first kind of Abel ordinary differential equation. Moreover, we show that, in special cases of dynamical interest, such an equation can be solved by quadrature. In particular we establish, for ordinary potential functions, a classical formula obtained in different way by Joukowsky for a particle moving on a surface.Work performed with the support of the Gruppo Nazionale di Fisica Matematica (G.N.F.M.) of the Italian National Research Council.  相似文献   

Oil-generation kinetics for organic facies with Type-II and -IIS kerogen in the Menilite Shales of the Polish Carpathians     

M.D. Lewan  M.J. Kotarba  D. Wi?c?aw 《Geochimica et cosmochimica acta》2006,70(13):3351-3368

The Menilite Shales (Oligocene) of the Polish Carpathians are the source of low-sulfur oils in the thrust belt and some high-sulfur oils in the Carpathian Foredeep. These oil occurrences indicate that the high-sulfur oils in the Foredeep were generated and expelled before major thrusting and the low-sulfur oils in the thrust belt were generated and expelled during or after major thrusting. Two distinct organic facies have been observed in the Menilite Shales. One organic facies has a high clastic sediment input and contains Type-II kerogen. The other organic facies has a lower clastic sediment input and contains Type-IIS kerogen. Representative samples of both organic facies were used to determine kinetic parameters for immiscible oil generation by isothermal hydrous pyrolysis and S₂ generation by non-isothermal open-system pyrolysis. The derived kinetic parameters showed that timing of S₂ generation was not as different between the Type-IIS and -II kerogen based on open-system pyrolysis as compared with immiscible oil generation based on hydrous pyrolysis. Applying these kinetic parameters to a burial history in the Skole unit showed that some expelled oil would have been generated from the organic facies with Type-IIS kerogen before major thrusting with the hydrous-pyrolysis kinetic parameters but not with the open-system pyrolysis kinetic parameters. The inability of open-system pyrolysis to determine earlier petroleum generation from Type-IIS kerogen is attributed to the large polar-rich bitumen component in S₂ generation, rapid loss of sulfur free-radical initiators in the open system, and diminished radical selectivity and rate constant differences at higher temperatures. Hydrous-pyrolysis kinetic parameters are determined in the presence of water at lower temperatures in a closed system, which allows differentiation of bitumen and oil generation, interaction of free-radical initiators, greater radical selectivity, and more distinguishable rate constants as would occur during natural maturation. Kinetic parameters derived from hydrous pyrolysis show good correlations with one another (compensation effect) and kerogen organic-sulfur contents. These correlations allow for indirect determination of hydrous-pyrolysis kinetic parameters on the basis of the organic-sulfur mole fraction of an immature Type-II or -IIS kerogen.  相似文献   

Response to the comment by V. Neck on “Hydrolysis of neptunium(V) at variable temperatures (10-85 °C)”, Geochimica et Cosmochimica Acta 68, 4821-4830     

Linfeng Rao  Thandankorai G. Srinivasan  PierLuigi Zanonato  Plinio Di Bernardo 《Geochimica et cosmochimica acta》2006,70(17):4556-4562

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Elucidation of different forms of organic carbon in marine sediments from the Atlantic coast of Spain using thermal analysis coupled to isotope ratio and quadrupole mass spectrometry     

Elisa Lopez Capel  Jos Maria de la Rosa Arranz  Francisco J. Gonzlez-Vila  Jos Antonio Gonzlez-Perez  David A.C. Manning 《Organic Geochemistry》2006,37(12):1983

Analysis of river, estuary and marine sediments from the Atlantic coast of Spain using thermogravimetry–differential scanning calorimetry–quadrupole mass spectrometry–isotope ratio mass spectrometry (TG–DSC–QMS–IRMS) was used to (a) distinguish bulk chemical hosts for C within a sediment and humic acid fraction, (b) track C pools with differing natural C isotope ratios and (c) observe variation with distance from the coast. This is the first application of such a novel method to the characterisation of organic matter from marine sediments and their corresponding humic acid fractions. Using thermal analysis, a labile, a recalcitrant and a refractory carbon pool can be distinguished. Extracted humic fractions are mainly of recalcitrant nature. The proportion of refractory carbon is greatest in marine sediments and humic acid fractions. Quadrupole mass spectrometry confirmed that the greatest proportion of m/z 44 (CO₂) and m/z 18 (H₂O) were detected at temperatures associated with recalcitrant carbon (510–540 °C). Isotope analysis detected progressive enrichment in δ¹³C for the sediment samples with an increase in marine influence. Isotopic heterogeneity in the refractory organic matter in marine sediments could be due to products of anthropogenic origin or natural combustion products. Isotope homogeneity of humic acids confirms the presence of terrigenous C in marine sediments, allowing the terrestrial input to be characterised.  相似文献   

HP–LT Variscan metamorphism in the Cubito-Moura schists (Ossa-Morena Zone, southern Iberia)     

Guillermo Booth-Rea  Jos Fernando Simancas  Antonio Azor  Jos Miguel Azan  Francisco Gonzlez-Lodeiro  Paulo Fonseca 《Comptes Rendus Geoscience》2006,338(16):1260-1267

Multi-equilibrium thermobarometry shows that low-grade metapelites (Cubito-Moura schists) from the Ossa–Morena Zone underwent HP–LT metamorphism from 340–370 °C at 1.0–0.9 GPa to 400–450 °C at 0.8–0.7 GPa. These HP–LT equilibriums were reached by parageneses including white K mica, chlorite and chloritoid, which define the earliest schistosity (S₁) in these rocks. The main foliation in the schists is a crenulation cleavage (S₂), which developed during decompression from 0.8–0.7 to 0.4–0.3 GPa at increasing temperatures from 400–450 °C to 440–465 °C. Fe³⁺ in chlorite decreased greatly during prograde metamorphism from molar fractions of 0.4 determined in syn-S₁ chlorites down to 0.1 in syn-S₂ chlorites. These new data add to previous findings of eclogites in the Moura schists indicating that a pile of allochtonous rocks situated next to the Beja-Acebuches oceanic amphibolites underwent HP–LT metamorphism during the Variscan orogeny. To cite this article: G. Booth-Rea et al., C. R. Geoscience 338 (2006).  相似文献