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251.
252.
Geochemical heterogeneities and dynamics of magmas within the plumbing system of a persistently active volcano: evidence from Stromboli 总被引:1,自引:0,他引:1
We report here the most complete dataset for major and trace elements, as well as Sr isotopic compositions, of magmas erupted
by Stromboli since the onset of present-day activity 1,800 years ago. Our data relate to both porphyritic scoria and lava
originating in the uppermost parts of the feeding system, plus crystal-poor pumice produced by paroxysmal explosive eruption
of deep-seated, fast ascending, magma. The geochemical variations recorded by Stromboli’s products allow us to identify changes
in magma dynamics affecting the entire plumbing system. Deep-seated magmas vary in composition between two end-members having
different key ratios in strongly incompatible trace elements and Sr isotopes. These features may be ascribed to mantle source
processes (fluid/melt enrichment, variable degrees of melting) and occasional contamination by deep, mafic, cumulates. Temporal
trends reveal three phases during which magmas with distinct geochemical signatures were erupted. The first phase occurred
between the third and fourteenth centuries AD and was characterised by the eruption of evolved magmas sharing geochemical
and Sr isotopic compositions similar to those of earlier periods of activity (<12 ka—Neostromboli and San Bartolo). The second
phase, which began in the sixteenth century and lasted until the first half of the twentieth century, produced more primitive,
less radiogenic, magmas with the lowest Ba/La and Rb/Th ratios of our dataset. The last phase is ongoing and is marked by
a magma having the lowest Sr isotopic composition and highest Rb/Th ratio of the dataset. While this new magma can be clearly
identified in the pumice erupted during the last two paroxysmal eruptions of 2003 and 2007, shallow degassed magma extruded
during this time span records significant geochemical and isotopic heterogeneities. We thus suggest that the shallow reservoir
has been only partially homogenised by this new magma influx. We conclude that compositional variations within the shallow
magma system of a persistently active volcano provide only a biassed signal of ongoing geochemical changes induced by deep
magma refilling. We argue that source changes can only be identified by interpreting the geochemistry of pumice, because it
reliably represents magma transferred directly from deep portions of the plumbing system to the surface. 相似文献
253.
长白山天池火山全新世3期浮岩长石斑晶中熔体包裹体高温热台实验研究 总被引:1,自引:0,他引:1
长白山天池火山在全新世曾多次喷发,以往研究结果基本上认定至少有3期喷发物:距今约5,000a前淡黄色碱流质浮岩、距今约1,000a前灰白色碱流质浮岩和碎屑流以及距今约300a的黑色粗面质浮岩和熔结凝灰岩。喷发物斑晶矿物中含有众多熔体包裹体,形貌特征各有不同。经Leitz1350高温热台对天池火山全新世3期喷发物长石中熔体包裹体的均一法测温实验,结果表明第1,3喷发期的岩浆温度相差不大,而千年大喷发期较为复杂,揭示当时有2个不同温度段的熔体存在,为大喷发可能由2种岩浆注入和混合而触发的论点提供了线索。实验还证实,个体小的熔体包裹体易于均一,而个体较大的、尤其是含有大量子晶的熔体包裹体则很难均一;均一温度与熔体包裹体大小、何时从较快升温速率变为较慢升温速率、是否为初次升温时测量得出有关。同一颗熔体包裹体多次数升温至均一,每次得到的均一温度不同,而且每升温一次得到的均一温度均比前一次高,证实了均一过程中的确有H扩散的现象 相似文献
254.
Nicolas Bourguet Madeleine Goutx Jean-Franois Ghiglione Mireille Pujo-Pay Genevive Mvel Andr Momzikoff Laure Mousseau Catherine Guigue Nicole Garcia Patrick Raimbault Romain Pete Louise Oriol Dominique Lefvre 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1454-1469
This study investigated the relationships between dissolved organic matter (DOM) composition and bacterial dynamics on short time scale during spring mesotrophic (March 2003) and summer oligotrophic (June 2003) regimes, in a 0–500 m depth water column with almost no advection, at the DYFAMED site, NW Mediterranean. DOM was characterized by analyzing dissolved organic carbon (DOC), colored dissolved organic matter (CDOM) and lipid class biotracers. Bacterial dynamic was assessed through the measurement of in situ bacterial lipase activity, abundance, production and bacterial community structure. We made the assumption that by coupling the ambient concentration of hydrolysable acyl-lipids with the measurement of their in situ bacterial hydrolysis rates (i.e. the free fatty acids release rate) would provide new insights about bacterial response to change in environmental conditions. The seasonal transition from spring to summer was accompanied by a significant accumulation of excess DOC (+5 μM) (ANOVA, p<0.05, n=8) in the upper layer (0–50 m). In this layer, the free fatty acids release rate to the bacterial carbon demand (BCD) ratio increased from 0.6±0.3 in March to 1.3±1.0 in June (ANOVA, p<0.05, n=8) showing that more uncoupling between the hydrolysis of the acyl-lipids and the BCD occurred during the evolution of the season, and that free fatty acids contributed to the excess DOC. The increase of lipolysis index and CDOM absorbance (from 0.24±0.17 to 0.39±0.13 and from 0.076±0.039 to 0.144±0.068; ANOVA, p<0.05, n=8, respectively), and the higher contribution of triglycerides, wax esters and phospholipids (from <5% to 12–31%) to the lipid pool reflected the change in the DOM quality. In addition to a strong increase of bacterial lipase activity per cell (51.4±29.4–418.3±290.6 Ag C cell−1 h−1), a significant percentage of ribotypes (39%) was different between spring and summer in the deep chlorophyll maximum (DCM) layer in particular, suggesting a shift in the bacterial community structure due to the different trophic conditions. At both seasons, in the chlorophyll layers, diel variations of DOM and bacterial parameters reflected a better bioavailability and/or DOM utilization by bacteria at night (the ratio of free fatty acids release rate to bacterial carbon demand decreased), most likely related to the zooplankton trophic behaviour. In mesotrophic conditions, such day/night pattern was driving changes in the bacterial community structure. In more oligotrophic period, diel variations in bacterial community structure were depth dependent in relation to the strong summer stratification. 相似文献
255.
Very few coral reefs are located close enough to large cities to study the influence of large urban populations on reef assemblages. An exception is the Thousand Islands reef complex to the north of Jakarta, the capital city of Indonesia, and one of the largest conurbations in the world. Here we present data from a detailed survey where sponge assemblages were assessed at 30 patch reefs associated with islands in three coastal zones along an in-to-offshore gradient. Sponge assemblages are described at three taxonomic levels of detail (species, genus and family level). We recorded a total of 118 sponge species, 64 genera and 36 families, Aaptos suberitoides (Brønsted, 1934), Clathria (Thalysias) reinwardti (Vosmaer, 1880), Petrosia (Petrosia) nigricans (Lindgren, 1897) and Xestospongia testudinaria (Lamarck, 1813) were the most common species overall. There was a pronounced difference in composition among zones with the most distinct difference between the inshore zone and the other two zones. The inshore environment was characterised by very high turbidity and low live coral cover; the dominant substrate consisted of algal turf and sand. Environmental conditions improved and sponge diversity increased further offshore, although most areas appeared to have been affected by some form of disturbance. Ordinations were also largely congruent, at species, generic and family levels of taxonomic resolution. This indicates that variation in composition at higher taxonomic levels is a good indicator of variation at lower taxonomic levels, at least when there is a pronounced environmental gradient. 相似文献
256.
257.
Nicole A. Stroncik Andreas Klügel Thor H. Hansteen 《Contributions to Mineralogy and Petrology》2009,157(5):593-607
A thermobarometric and petrologic study of basanites erupted from young volcanic cones along the submarine portions of the
three El Hierro rift zones (NE-Rift, NW-Rift and S-Ridge) has been performed to reconstruct magma plumbing and storage beneath
the island. Mineral-melt thermobarometry applied to naturally quenched glass and clinopyroxene rims yields pressures ranging
from 350 to 1070 MPa with about 80% of the calculated pressures being in the range of 600–800 MPa. This corresponds to a depth
range of 19–26 km, implying that the main level of final crystal fractionation is within the uppermost mantle. No systematic
dependence between sample locality and fractionation pressures could be observed. Olivine and clinopyroxene crystals in the
rocks are complexly zoned and have, on an inter-sample as well as on an intra-sample scale, highly variable core and rim compositions.
This can best be explained by mixing of multiply saturated (olivine, magnetite, clinopyroxene, ilmenite), moderately evolved
magmas with more mafic magmas being either only saturated with olivine + spinel or with olivine + spinel + clinopyroxene.
The inter-sample differences indicate derivation from small, isolated magma chambers which have undergone distinct fractionation
and mixing histories. This is in contrast to oceanic intraplate volcanoes situated on plumes with high melt supply rates,
e.g. Kilauea Volcano (Hawaii), where magma is mainly transported through a central conduit system and stored in a shallow
magma chamber prior to injection into the rift zones. The plumbing system beneath El Hierro rather resembles the magma storage
systems beneath, e.g. Madeira or La Palma, indicating that small, intermittent magma chambers might be a common feature of
oceanic islands fed by plumes with relatively low fluxes, which results in only limited and periodic magma supply. 相似文献
258.
Jennyfer Miot Karim Benzerara Andreas Kappler Martin Obst Fériel Skouri-Panet Nicole Posth Gordon E. Brown Jr. François Guyot 《Geochimica et cosmochimica acta》2009,73(3):696-1446
Minerals formed by bio-oxidation of ferrous iron (Fe(II)) at neutral pH, their association with bacterial ultrastructures as well as their impact on the metabolism of iron-oxidizing bacteria remain poorly understood. Here, we investigated iron biomineralization by the anaerobic nitrate-dependent iron-oxidizing bacterium Acidovorax sp. strain BoFeN1 in the presence of dissolved Fe(II) using electron microscopy and Scanning Transmission X-ray Microscopy (STXM). All detected minerals consisted mainly of amorphous iron phosphates, but based on their morphology and localization, three types of precipitates could be discriminated: (1) mineralized filaments at distance from the cells, (2) globules of 100 ± 25 nm in diameter, at the cell surface and (3) a 40-nm thick mineralized layer within the periplasm. All of those phases were shown to be intimately associated with organic molecules. Periplasmic encrustation was accompanied by an accumulation of protein moieties. In the same way, exopolysaccharides were associated with the extracellular mineralized filaments. The evolution of cell encrustation was followed by TEM over the time course of a culture: cell encrustation proceeded progressively, with rapid precipitation in the periplasm (in a few tens of minutes), followed by the formation of surface-bound globules. Moreover, we frequently observed an asymmetric mineral thickening at the cell poles. In parallel, the evolution of iron oxidation was quantified by STXM: iron both contained in the bacteria and in the extracellular precipitates reached complete oxidation within 6 days. While a progressive oxidation of Fe in the bacteria and in the medium could be observed, spatial redox (oxido-reduction state) heterogeneities were detected at the cell poles and in the extracellular precipitates after 1 day. All these findings provide new information to further the understanding of molecular processes involved in iron biomineralization by anaerobic iron-oxidizing bacteria and offer potential signatures of those metabolisms that can be looked for in the geological record. 相似文献
259.
Assessing climate change vulnerability in the arctic using geographic information services in spatial data infrastructures 总被引:1,自引:1,他引:0
Timely knowing about climate change impacts is crucial to adequately plan and undertake adaptive measures and thus to effectively
lower vulnerability. This requires gathering and integrating geographic information on exposure, local response mechanisms
and stakeholders’ concerns. Spatial Data Infrastructures (SDI) are internet-based information systems that facilitate the
exchange and use of distributed geographic information. This paper presents the application of SDI to climate change assessment
by implementing a generic methodology for the quantification of vulnerability to climate change. The resulting integrated
tool allows scientists, stakeholders and decision makers to communicate, assess and improve information about vulnerability
to climate change. We show how emerging internet technologies and SDI in particular, make a new interactive approach of assessing
vulnerability to climate change possible. Vulnerability was quantified based on an active stakeholder involvement by incorporating
their varying perceptions, by allowing them to provide feedback and by supporting the acquisition of stakeholders’ knowledge.
However, the application showed that to be effective, efforts to achieve and maintain interoperability between the various
scientific disciplines should be kept integrated within mainstream IT developments. 相似文献
260.
Results from a suite of 30-year simulations (after spin-up) of the fully coupled Community Climate System Model version 2.0.1
are analyzed to examine the impact of doubling CO2 on interactions between the global water cycle and the regional water cycles of four similar-size, but hydrologically and
thermally different study regions (the Yukon, Ob, St Lawrence, and Colorado river basins and their adjacent land). A heuristic
evaluation based on published climatological data shows that the model generally produces acceptable results for the control
1× CO2 concentration, except for mountainous regions where it performs like other modern climate models. After doubling CO2, the Northern Hemisphere receives significantly (95% confidence level) more moisture from the Southern Hemisphere during
the boreal summer than under 1× CO2 conditions, and the phase of the annual cycle of net moisture transport to areas north of 60°N shifts to a month later than
in the reference simulation. Precipitation and evapotranspiration in the doubled CO2 simulation increase for the Yukon, Ob, and St Lawrence, but decrease, on average, for the Colorado region compared to the
reference simulation. For all regions, interaction between global and regional water cycles increases under doubled CO2, because the amount of moisture entering and leaving the regions increases in the warmer climate. The degree of change in
this interaction depends on region and season, and is related to slight shifts in the position/strength of semi-permanent
highs and lows for the Yukon, Ob, and St Lawrence; in the Colorado region, higher temperatures associated with doubling CO2 and the anticyclone located over the region increase the persistence of dry conditions. 相似文献