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1.
Natural precipitation and water samples from passive devices were collected at Mt. Vesuvius and Vulcano Island, Italy, during the period 2004–2006, in order to investigate its possible interactions with fumarolic gases. Evidence of chemical reactions between fumarolic fluids and rain samples before and after its deposition into the sampling devices was found at Vulcano Island. Very low pH values (down to 2.5) and significant amounts of chlorine and sulfate (up to 22 mEq/l) were measured at sampling points located close to the fumarolic field. In contrast, anthropogenic contributions and/or dissolution of aerosols (both maritime and continental) influence the chemistry of rainwaters at Mt. Vesuvius, which show inter-annual variations that are highly consistent with those recorded at the coastal site at Vulcano Island. Chemistry of waters directly exposed to fumarolic fluids may then give useful information about its temporal evolution, holding the signal of the “maximum” chemical event occurred in the meanwhile. In addition, the observation of the health status of vegetation colonizing the immediate surroundings of the fumarolic fields, due to its strong dependence on the interactions with these fluids, may work as a possible biomarker of volcanic activity.  相似文献   

2.
梅冥相 《古地理学报》2011,13(4):363-374
在高倍(＞50000x)扫描电子显微镜(SEM)、原子显微镜(AFM)或透射电子显微镜(TEM)下,那些在岩石和矿物中所见到的纳米级别的物体常常吸引了地质学家们的注意.这些物体大小在25～300 nm之间,多呈球状、棒状或卵圆状;对这些物体的成因,存在不同的看法而导致了剧烈的争论.因为这些物体与真菌中的球菌和杆菌总体相...  相似文献   

3.
Zusammenfassung Unterwasserbeobachtungen im sublitoralen Solfatarenfeld von Vulcano brachten Einzelheiten über die verschiedene Gestaltung des Meeresbodenreliefs im Bereich der Gasaustritte und über die Anlagerung von kolloidalem Schwefel. Die Befunde werden anhand mehrerer Unterwasserphotographien erläutert und es wird auf die Ähnlichkeit der rezenten Bodengestaltung mit gewissen aus triadischen Pb-Zn-Erzlagerstätten bekannten Gefügen hingewiesen. Hinweise auf Flora und Fauna im Bereich der submarinen Vulkanexhalationen ergänzen die Untersuchungen.
Underwater studies in the sublitoral field of solfataras of Vulcano revealed details on the relief of the sea bottom in areas with volcanic exhalations and on the deposition of colloidal sulphur. The observations made are illustrated by several underwater photographs. The similarity between the recent shape of the ground and certain fabrics known from Triassic Pb-Zn- ore deposits is pointed out. These studies are supplemented by short data on the abundant flora and fauna in the area of the submarine volcanic exhalations.
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4.
We present here new measurements of sulfur dioxide and hydrogen sulfide emissions from Vulcano, Etna, and Stromboli (Italy), made by direct sampling at vents and by filter pack and ultraviolet spectroscopy in downwind plumes. Measurements at the F0 and FA fumaroles on Vulcano yielded SO2/H2S molar ratios of ≈0.38 and ≈1.4, respectively, from which we estimate an H2S flux of 6 to 9 t · d−1 for the summit crater. For Mt. Etna and Stromboli, we found SO2/H2S molar ratios of ≈20 and ≈15, respectively, which combined with SO2 flux measurements, suggest H2S emission rates of 50 to 113 t · d−1 and 4 to 8 t · d−1, respectively. We observe that “source” and plume SO2/H2S ratios at Vulcano are similar, suggesting that hydrogen sulfide is essentially inert on timescales of seconds to minutes. This finding has important implications for estimates of volcanic total sulfur budget at volcanoes since most existing measurements do not account for H2S emission.  相似文献   

5.
Quartz-rich xenoliths in lavas and pyroclastic rocks from VulcanoIsland, part of the Aeolian arc, Italy, contain silicic meltinclusions with high SiO2 (73–80 wt %) and K2O (3–6wt %) contents. Two types of inclusions can be distinguishedbased on their time of entrapment and incompatible trace element(ITE) concentrations. One type (late, ITE-enriched inclusions)has trace element characteristics that resemble those of themetamorphic rocks of the Calabro-Peloritano basement of theadjacent mainland. Other inclusions (early, ITE-depleted) havevariable Ba, Rb, Sr and Cs, and low Nb, Zr and rare earth element(REE) contents. Their REE patterns are unfractionated, witha marked positive Eu anomaly. Geochemical modelling suggeststhat the ITE-depleted inclusions cannot be derived from equilibriummelting of Calabro-Peloritano metamorphic rocks. ITE-enrichedinclusions can be modelled by large degrees (>80%) of meltingof basement gneisses and schists, leaving a quartz-rich residuerepresented by the quartz-rich xenoliths. Glass inclusions inquartz-rich xenoliths represent potential contaminants of Aeolianarc magmas. Interaction between calc-alkaline magmas and crustalanatectic melts with a composition similar to the analysed inclusionsmay generate significant enrichment in potassium in the magmas.However, ITE contents of the melt inclusions are comparablewith or lower than those of Vulcano calc-alkaline and potassicrocks. This precludes the possibility that potassic magmas inthe Aeolian arc may originate from calc-alkaline parents throughdifferent degrees of incorporation of crustal melts. KEY WORDS: melt inclusions; crustal anatexis; magma assimilation; xenoliths; Vulcano Island  相似文献   

6.
This paper investigates the role played by the fumarolic plume of a passive degassing volcano in the genesis of rock coatings (RC) and in the introduction and re-distribution of metals and trace elements in the surficial environment. At La Fossa active volcano (Vulcano Island) and in the surrounding environment RC develop owing to exposure of the ground surface to the volcanic acid plume produced by the passive degassing of La Fossa. Significant positive anomalies of a wide variety of metals and trace elements (including Bi, Ag, Se, Te, Sb, Pb, As, Cu, Tl and Cd) were observed either in distal and proximal RC. Most of these anomalies are interpreted to be the result of the transport and subsequent deposition of trace elements, likely to form volatile compounds, in the fumarolic plume. Two main processes seem to control the geochemistry of RC: one is represented by the leaching and subsequent deposition of elements from the proximal toward the distal RC; the other is the direct input of trace elements carried by the emitted volcanic aerosol. The fact that most of the trace elements (particularly Pb, As, Tl, Bi, Te, Se, Cd) enriched in the RC of Vulcano are highly toxic and potentially dangerous to health in high concentration, indicates that the atmospheric metal injection by the quiescently degassing La Fossa volcano together with the subsequent deposition and remobilization by means of surficial waters may represent an environmental hazard that should be taken into account in evaluating the potential impact of volcanic air pollution on human health.  相似文献   

7.
Mineralogy and Petrology - Vulcano is part of the Aeolian volcanic arc in the southern Tyrrhenian Sea. Its products were emplaced through multiple episodes of edifice building and collapse since...  相似文献   

8.
The tectonic deformation of the Lipari–Vulcano complex, one of the most important active volcanic areas of the Mediterranean region, is studied here through the analysis of 10 years (1996–2006) of GPS data from both three permanent and 13 non‐permanent stations. This area can be considered crucial for the understanding of the interaction between the Eurasian and African plates in the Mediterranean area, and, in general, this work emphasizes a methodological approach, already applied in other areas worldwide ( J. Geophys. Res., 1996, 101 , 27 957 ; J. Geodyn., 1999, 27 , 213 ) where geodetic data and strain parameters maps of critical areas can help to improve our understanding of their geodynamical aspects. In this framework, this study is aimed at providing a kinematic deformation model on the basis of the dense geodetically estimated velocities of the Lipari–Vulcano complex. In particular, the observed deformation pattern can be described by a combination of (1) the main N–S regional compression and (2) a NNE–SSW compression with a small right‐lateral strike slip component acting along a tectonic structure trending N°40W between the two islands. This pattern was inspected through a simplified synthetic model.  相似文献   

9.
Schlieren are trains of platy or blocky minerals, typically the ferromagnesian minerals and accessory phases, that occur in granites and melt‐rich migmatites, such as diatexites. They have been considered as: (1) unmelted residue from xenoliths or the source region; (2) mineral accumulations formed during magma flow; (3) compositional layering; and (4) sites of melt loss. In order to help identify schlieren‐forming processes in the diatexites at St Malo, differences in the size, shape, orientation, distribution and composition of the biotite from schlieren and from their hosts have been investigated. Small biotite grains are much less abundant in the schlieren than in their hosts. Schlieren biotite grains are generally larger, have greater aspect ratios and have, except in hosts with low (< 10%) biotite contents, a much stronger shape preferred orientation than host biotite. The compositional ranges of host and schlieren biotite are similar, but schlieren biotite defines tighter, sharper peaks on composition‐frequency plots. Hosts show magmatic textures such as imbricated (tiled), unstrained plagioclase. Some schlieren show only magmatic textures (tiled biotite, no crystal‐plastic strain features), but many have textures indicating submagmatic and subsolidus deformation (e.g. kinked grains) and these schlieren show the most extensive evidence for recrystallization. Magmas at St Malo initially contained a significant fraction of residual biotite and plagioclase crystals; smaller biotite grains were separated from the larger plagioclase crystals during magma flow. Since plagioclase was also the major, early crystallizing phase, the plagioclase‐rich domains developed rapidly and reached the rigid percolation threshold first, forcing further magma flow to be concentrated into narrowing melt‐rich zones where the biotite had accumulated, hence increasing shear strain and the degree of shape preferred orientation in these domains. Schlieren formed in these domains as a result of grain contacts and tiling in the grain inertia‐regime. Final amalgamation of the biotite aggregates into schlieren involved volume loss as melt trapped between grains was expelled after the rigid percolation threshold was reached in the biotite‐rich layers.  相似文献   

10.
《Applied Geochemistry》1997,12(2):213-224
In March 1994, soil gases were sampled in the area of Vulcano Porto, on the island of Vulcano, using a grid of about 200 points/km2. Analysed gases were CO2, He and222Rn and, over a smaller area, H2S. Some of the samples were also analysed for the isotope composition of CO2C. Three anomalous CO2 degassing areas were identified: Grotta dei Palizzi, the area near the Telephone Exchange, and the area near the beach fumaroles. The behaviour of He and222Rn is different in these 3 areas. The concentration of He is much lower than that of atmospheric He (down to −3950 ppb) in the isthmus, and only in the area near Grotta dei Palizzi does it have values significantly higher than atmospheric ones (up to 1900 ppb). The activity of222Rn, always significantly positively related to CO2 concentrations, peaked in the 2 fumarole areas (isthmus, Telephone Exchange).  相似文献   

11.
 The aim of this paper is to verify whether lichens have the capacity to accumulate atmospheric contaminators linked to volcanic activity. About 100 lichens were collected in 1994 and 1995 from two active volcanic areas in Italy: Mount Etna and Vulcano Island. Twenty-seven elements were analyzed for each individual lichen using Instrumental Neutronic Activation Analysis and Inductively Coupled Plasma-Mass Spectrometry. Lichen composition reflects the contribution of the volcanic particulate material, and the two areas investigated can be distinguished on the basis of the concentration of some lithophile elements. Moreover, the distribution in lichens of the elements (As, Sb, Br, Pb) – derived from gas emissions (plume, fumaroles) – also shows different geochemical trends on Mt. Etna and Vulcano. Received: 20 April 1998 · Accepted: 4 July 1998  相似文献   

12.
Summary Pyroclastites erupted from the Upper Pollara magma chamber (13 ka, Salina Island, Aeolian Archipelago) resulted from mingling and mixing of rhyolitic and andesitic magmas. An experimental study has been conducted on the rhyolitic end-member to constrain the pre-eruptive conditions of the magma. In order to check for the role of mixing on the equilibrium phase assemblage, three different starting compositions, corresponding to three different mixing degrees, have been used. The crystallization experiments were conducted at two different oxygen fugacities and at variable temperature and fluid contents. The results indicate that the natural mineralogical assemblage can only be reproduced from a composition showing a certain degree of mixing. Assuming a pressure of 200 MPa (generally accepted for the Aeolian Islands), the pre-eruptive temperature of the magmas is estimated between 755 and 800 °C and the water content of the melt was higher than 4–4.5 wt.%. The Upper Pollara magma crystallized at relatively high fO2 (ΔlogfO2 = Ni–NiO + 1 log unit), compared to rhyolitic magmas from Lipari and Vulcano. As this difference has not been observed for the most primitive magmas the difference in fO2 could be related to different degassing processes operating in Salina and Lipari – Vulcano magmas.  相似文献   

13.
From their birth as condensates in the outflows of oxygen-rich evolved stars, processing in interstellar space, and incorporation into disks around new stars, amorphous silicates predominate in most astrophysical environments. Amorphous silicates were a major building block of our Solar System and are prominent in infrared spectra of comets. Anhydrous interplanetary dust particles (IDPs) thought to derive from comets contain abundant amorphous silicates known as GEMS (glass with embedded metal and sulfides) grains. GEMS grains have been proposed to be isotopically and chemically homogenized interstellar amorphous silicate dust. We evaluated this hypothesis through coordinated chemical and isotopic analyses of GEMS grains in a suite of IDPs to constrain their origins. GEMS grains show order of magnitude variations in Mg, Fe, Ca, and S abundances. GEMS grains do not match the average element abundances inferred for ISM dust containing on average, too little Mg, Fe, and Ca, and too much S. GEMS grains have complementary compositions to the crystalline components in IDPs suggesting that they formed from the same reservoir. We did not observe any unequivocal microstructural or chemical evidence that GEMS grains experienced prolonged exposure to radiation.We identified four GEMS grains having O isotopic compositions that point to origins in red giant branch or asymptotic giant branch stars and supernovae. Based on their O isotopic compositions, we estimate that 1-6% of GEMS grains are surviving circumstellar grains. The remaining 94-99% of GEMS grains have O isotopic compositions that are indistinguishable from terrestrial materials and carbonaceous chondrites. These isotopically solar GEMS grains either formed in the Solar System or were completely homogenized in the interstellar medium (ISM). However, the chemical compositions of GEMS grains are extremely heterogeneous and seem to rule out this possibility. Based on their solar isotopic compositions and their non-solar elemental compositions we propose that most GEMS grains formed in the nebula as late-stage non-equilibrium condensates.  相似文献   

14.
A structural analysis carried out on the volcanic products of the islands of Salina, Lipari and Vulcano (Aeolian archipelago) points out that the large-scale tectonic setting is dominated by NW-SE trending right-lateral extensional strike-slip faults and by N-S to NE-SW trending normal faults and fractures. This fault pattern generates pull-apart type structures, developing between different right-hand overlapping fault segments and a characteristic extensional imbricate fan geometry at the tip of the major strike-slip faults. All the structures, representing the surface expression of an active crustal discontinuity which controls the evolutionary history of the magmatism of the three islands, are kinematically compatible with a N100°E extension related to a rifting process affecting southern Italy.  相似文献   

15.
Along a NW-SE profile through the basement core, starting below the sedimentary unconformity and ending in the center of the nearly circular structure, the constituent quartz grains and their fluid inclusions exhibit the following characteristics:In the NW, fluid inclusions composed of CO2 and occasionally up to 50 Vol.% H2O occur along shock-induced planar elements following predominently {0 0 0 1} of coarse, largely unrecrystallized quartz grains. The planar elements are partly still open microcracks, partly they are healed, the fluid inclusions decorating the former sites of the cracks. Along these planar elements recrystallization into fine grained new quartz fabrics starts, this process increasing decidedly towards the southeast; nevertheless fluid inclusions are still retained. — Near and within the center of the dome the formerly coarse quartz grains are completely recrystallized to medium grained annealing fabrics, in which — surprizingly — the fluid inclusions have often retained their original positions relative to the old grains, so that their planar alignment now traverses the new grain boundaries. Here the enclosed fluid is pure CO2 as far as can be determined.On the basis of the homogenization temperatures of the fluid inclusions measured, and of independent petrologic geothermometry of the basement rocks near the center, the fluids trapped after the shock event had exhibited partial pressures of CO2 as high as 3 kbars at temperatures around 850° C. The derivation of these CO2-rich, post-shock fluids is either through release of older fluid inclusions from the lower crustal granulites affected by the catastrophic shattering event, or it is from a direct mantle source that might be genetically connected with the Vredefort event itself.  相似文献   

16.
It has been assumed that soil pendants form in a similar manner as stalactites, in which innermost laminae are the oldest and outer laminae are the youngest. This study presents a new interpretation for soil pendant development. Pahranagat Valley, Nevada, pendants contain features indicating continued precipitation through time at the clast–pendant contact, implying that the oldest deposits are not always found at the pendant–clast contact, as other studies have assumed. These features include a void at the clast–pendant contact where minerals such as calcium carbonate, silica, and/or fibrous silicate clays precipitate. In addition, fragments of the parent clast and detrital grains are incorporated into the pendant and are displaced and/or dissolved and result in the formation of sepiolite. This study indicates that pendants are complex, open systems that during and after their formation undergo chemical changes that complicate their usefulness for dating and paleoenvironmental analyses.  相似文献   

17.
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18.
G. Poli  D. Perugini 《Lithos》2002,65(3-4):287-297
Magma mixing structures from three different lava flows (Salina, Vulcano and Lesbos) are studied in order to assess the possible chaotic origin of magma mixing processes. Structures are analysed using a new technique based on image analysis procedures that extract time series that are representative of the relative change in composition through the structures. These time series are then used to reconstruct the attractors underlying the magma mixing process and to calculate the fractal dimension of the attractors. Results show that attractors exist and possess fractional dimensions. This evidence suggests that the mixing of magmas is a chaotic process governed by a low number of degrees of freedom. In addition, fractal dimension analyses allows us to discriminate between different regimes of mixing in the three lava flows. In particular our analyses suggest that the lava flow of Salina underwent more turbulent mixing than the lava flows of Lesbos and Vulcano.  相似文献   

19.
Mixing was an important process in the early solar nebula and is often used as an argument to explain the compositional scatter among chondrules—mm-sized, once molten silicate spherules in chondritic meteorites. If it is hypothesized that chondrules only acted as closed systems and the scatter in chondrule bulk chemical compositions is only the result of mixing heterogeneous precursor grains—the basic components of chondrules—, it is in turn possible to determine the sizes of the precursor grains using statistical calculations. In order to reproduce the observed compositional scatter in chondrules not more than ∼10 precursor grains should contribute to a single chondrule, each with a diameter of several 100 μm. This finding has important implications for the conditions of chondrule formation and replaces the so far widely accepted model that chondrules formed from fine-grained “dust-balls”. Chondrules rather formed from coarse-grained precursor aggregates with variable amounts of μm-fine matrix material. As a consequence, only chondrite matrix or interstellar material winnows as precursor material. Large grains of variable composition serving as precursor grains must have been formed prior to chondrule formation. Chondrules probably have not been their immediate precursors, as only 1-2 chondrule recycling steps would have homogenized bulk chondrule compositions. Chondrule recycling can therefore only have occurred to a limited extent. Chondrule formation needed at least three steps: (1) production of large and heterogeneous chondrule precursor grains, (2) agglomeration of large precursor grains and fine-grained precursors into aggregates, (3) formation of chondrules during transient heating events. Al-rich chondrules can in this context be explained by the admixture of CAIs to either chondrule precursors or a population of existing chondrules.  相似文献   

20.
Morphologies of placer platinum group minerals (PGM) are more variable and resistant to modification during transport than placer gold grains. This study documents morphological evolution of PGM placer grains during up to 120 km of transport in beach placers after river transport from inferred sources up to 200 km inland. PGM morphological changes are calibrated with changes in morphology of associated placer gold. Most of the PGM are Pt-Fe alloy and have been fed into the beach placer system from a large river at the western end of the beaches on the south coast of New Zealand. The incoming fluvial PGM suite includes Os, Ir and Ru alloys which may have been derived from distal ophiolitic sources. More proximal sources have Ural-Alaskan affinities and these contributed cooperite and braggite, or sperrylite, locally, as well as Pt-Fe alloy grains. Some PGM may have been recycled through Cretaceous-Quaternary fluvial sediments before entering the modern placer system. Recycled placer PGM grains have also been derived from elevated Quaternary beaches near the coastline. PGM grains entering beach placers have rough surfaces, with remnants of crystal faces, and these evolve to smooth flakes with progressive long-shore transport. PGM flakes have slightly thickened rims caused by impacts by saltating sand on windy beaches, and the most distal beach placers contain flakes with incipient toroidal shapes. These PGM incipient toroids are poorly developed compared to accompanying well-formed toroidal gold that has developed in nearly all beach placers, including those on elevated Quaternary beaches. Typical PGM and gold placer grain size decreases with increasing distance of transport, from fluvial grain size of 400–1,000 to ～200 microns on the most distal beaches, accompanied by eastward loss of equant PGM grains and associated increase in proportion of flakes. Although net transport distance is ～120 km in the beach placer complex, frequent aeolian transport of grains from beach to dunes and subsequent recycling by storm surges substantially increased total transport distance in a dynamic windy tectonic environment.  相似文献   

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