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21.
Spectra of Hα, Hβ and Hδ have been taken under good seeing conditions with the vacuum tower telescope of Sacramento Peak Observatory. Intensity curves are given at various wavelengths in these lines to permit further comparison with a theoretical model. Moreover, considering in each case the range of height in which the lines are almost optically thin and using a few approximations, the following results are derived: between 2000 and 6000 km above the limb the average thermal + turbulent velocity of the atoms is found to increase from 20 km s?1 to 30 km s?1 and the mean number of hydrogen atoms per cm3 in level 2 is given by $$\log n_2 {\text{ = }}4.5{\text{ }} - {\text{ 0}}{\text{.00056(}}z - 2000)$$ z being the altitude above the limb in km. For line profile computations a new interpolation formula is presented; it gives good profiles with a small number of scans, saving microphotometer time. 相似文献
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Many studies have argued for the contribution of at least three components, namely the mantle wedge, the subducted oceanic crust, and its sediment cover, to describe the geochemistry of island arc volcanics. However, isotope correlations reflecting a simple binary mixing can be observed at the scale of a single arc island or volcano. Here we investigate the possibility that these trends reflect pseudo-binary mixing relationships in a three-component system. We present a simplified, two-stage model for the systematic isotope modelling of a cogenetic suite of arc lavas. This includes metasomatism of portions of the mantle wedge by hydrous phases released from the down-going oceanic crust, and sediments, followed by progressive mixing and melting. A consequence of this model is that it leads to a two end-member mixing process from the mantle wedge, oceanic crust, and sediment components. To solve the model we reduce it to a step-by-step procedure combined with a Monte-Carlo simulation. The procedure consists of: (i) producing a large number of random values on each variable of the model; (ii) using the computed values to calculate the isotopic compositions of lavas; and (iii) comparing the obtained isotopic compositions with measured data. Applied to a new set of Sr, Nd, and Pb isotope data for volcanics (basalts, basaltic andesites, trachybasalts, and basaltic trachyandesites) from Merapi volcano (Java island, Sunda arc), the model successfully reproduces the binary mixing relationships previously documented for the medium-K and high-K lava series from this volcano, thus giving further support to the hypothesis that this distinction is inherited from the primary magmas and primarily reflects a property of the mantle source. The results allow identification of a set of numerical values for bulk partition coefficients (solid/hydrous fluid, and solid/H2O-rich melt) and variables (e.g., the mass ratio between the metasomatizing phase and the mantle wedge), which can be used for quantitative arc-lava petrogenetic calculations. They also require a direct relationship between dehydration of the slab and melting of the metasomatized mantle wedge. Finally, our evaluation shows that for isotope modelling of the Merapi lavas, the two-stage procedure is controlled more by the considered source components (mantle wedge, oceanic crust, sediments, and their derivatives) than by the various processes involved (dehydration, melting, and mixing). 相似文献
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Review: Microbial biocenoses in pristine aquifers and an assessment of investigative methods 总被引:2,自引:6,他引:2
The current knowledge of microbial biocenoses (communities) in pristine aquifers is presented in a review, which also discusses their relevance for questions of groundwater protection. Aquifers are heterogeneous on all scales and structured in a variety of habitats. The void spaces in many aquifers are small. The biocenoses are thus predominantly composed of microorganisms and, often, microinvertebrates. Larger voids and macroorganisms occur in karst cavities. Due to the absence of light, the biocenoses depend on chemical energy resources, which are, however, scarce in non-contaminated groundwater. The microorganisms thus show small cell sizes, low population densities and reduced activity; they developed specific strategies to survive oligotrophic conditions. The review also discusses the impact of contamination on the biocenoses, and the potential use of the biocenoses or specific organisms as indicators for groundwater quality, and the limits of this approach. Bacteria are either planktonic or attached to aquifer material, which requires both fluid and solid phase sampling. Most groundwater bacteria are viable but non-culturable. Consequently, cultivation techniques give an incomplete picture of the biocenoses, while methods from molecular microbiology provide genetic fingerprints of the entire community. Different analytical methods are available to count microorganisms, identify species, characterise microbial diversity, and measure activity. 相似文献
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The main result of this work is to show that macroseismic intensity decay with distance strongly depends on the epicentral intensity. An attenuation law that takes this parameter into account is proposed for Metropolitan France, from the analysis of SISFRANCE macroseismic database. Such a model significantly reduces the difference between observed and theoretical intensities. A map of the attenuation variations is also set up for Metropolitan France. No major site effects are observed, but at a broad scale, young Alpine regions display a stronger attenuation than old Hercynian regions. To cite this article: P. Arroucau et al., C. R. Geoscience 338 (2006). 相似文献
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Massimo Chiaradia Dave Banks Robert Cliff Robert Marschik Antoine de Haller 《Mineralium Deposita》2006,41(6):565-573
The origin of the hypersaline fluids (magmatic or basinal brine?), associated with iron oxide (Cu–U–Au–REE) deposits, is controversial. We report the first chlorine and strontium isotope data combined with Cl/Br ratios of fluid inclusions from selected iron oxide–copper–gold (IOCG) deposits (Candelaria, Raúl–Condestable, Sossego), a deposit considered to represent a magmatic end member of the IOCG class of deposit (Gameleira), and a magnetite–apatite deposit (El Romeral) from South America. Our data indicate mixing of a high δ 37Cl magmatic fluid with near 0‰ δ 37Cl basinal brines in the Candelaria, Raúl–Condestable, and Sossego IOCG deposits and leaching of a few weight percent of evaporites by magmatic-hydrothermal (?) fluids at Gameleira and El Romeral. The Sr isotopic composition of the inclusion fluids of Candelaria, Raúl–Condestable, and El Romeral confirms the presence of a non-magmatic fluid component in these deposits. The heavy chlorine isotope signatures of fluids from the IOCG deposits (Candelaria, Raúl–Condestable, Sossego), reflecting the magmatic-hydrothermal component of these fluids, contrast with the near 0‰ δ 37Cl values of porphyry copper fluids known from the literature. The heavy chlorine isotope compositions of fluids of the investigated IOCG deposits may indicate a prevailing mantle Cl component in contrast to porphyry copper fluids, an argument also supported by Os isotopes, or could result from differential Cl isotope fractionation processes (e.g. phase separation) in fluids of IOCG and porphyry Cu deposits. 相似文献
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The Irtysh river basin all the way from river spring in China across Kazakhstan as far as the Russian part of Siberia is among the most ecologically endangered and affected regions on our planet. The study provides a summary of the historical reasons for anthropological interventions in this area, which began with the construction of plants of the military—industrial complexes in the forties of the last century during World War II. These plants have a major share in extreme high concentrations of heavy metals in surface as well in groundwaters locally. The Semipalatinsk nuclear polygon plays a specific role as a source of contamination of local waters. The release of top secret data enabled us to gain knowledge about serious problems related to high radioactivity of groundwaters, which should spread uncontrollably through a system of secondary fissures activated by nuclear blasts. Another serious problem in this region is the quantitative aspect of contamination. Model simulations of water balance indicate that large industrial development in the spring area in China and continuously increasing water consumption in Kazakhstan may lead to desiccation of the lower stretch of this large river in Siberia during the summer months of 2030. 相似文献