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271.
Melt inclusions were examined in phenocrysts in basalt, andesite, dacite, and rhyodacite from the Karymskii volcanic center in Kamchatka and dacite form Golovnina volcano in Kunashir Island, Kuriles. The inclusions were examined by homogenization and by analyzing glasses in more than 80 inclusions on an electron microscope and ion microprobe. The SiO2 concentrations in the melt inclusions in plagioclase phenocrysts from basalts from the Karymskii volcanic center vary from 47.4 to 57.1 wt %, these values for inclusions in plagioclase phenocrysts from andesites are 55.7–67.1 wt %, in plagioclase phenocrysts from the dacites and rhyodacites are 65.9–73.1 wt %, and those in quartz in the rhyodacites are 72.2–75.7 wt %. The SiO2 concentrations in melt inclusions in quartz from dacites from Golovnina volcano range from 70.2 to 77.0 wt %. The basaltic melts are characterized by usual concentrations of major components (wt %): TiO2 = 0.7–1.3, FeO = 6.8–11.4, MgO = 2.3–6.1, CaO = 6.7–10.8, and K2O = 0.4–1.7; but these rocks are notably enriched in Na2O (2.9–7.4 wt % at an average of 5.1 wt %, with the highest Na2O concentration detected in the most basic melts: SiO2 = 47.4–52.0 wt %. The concentrations of volatiles in the basic melts are 1.6 wt % for H2O, 0.14 wt % for S, 0.09 wt % for Cl, and 50 ppm for F. The andesite melts are characterized by high concentrations (wt %) of FeO (6.5 on average), CaO (5.2), and Cl (0.26) at usual concentrations of Na2O (4.5), K2O (2.1), and S (0.07). High water concentrations were determined in the dacite and rhyodacite melts: from 0.9 to 7.3 wt % (average of 15 analyses equals 4.5 wt %). The Cl concentration in these melts is 0.15 wt %, and those of F and S are 0.06 and 0.01 wt %, respectively. Melt inclusions in quartz from the dacites of Golovnina volcano are also rich in water: they contain from 5.0 to 6.7 wt % (average 5.6 wt %). The comparison of melt compositions from the Karymskii volcanic center and previously studied melts from Bezymyannyi and Shiveluch volcanoes revealed their significant differences. The former are more basic, are enriched in Ti, Fe, Mg, Ca, Na, and P but significantly depleted in K. The melts of the Karymskii volcanic center are most probably less differentiated than the melts of Bezymyannyi and Shiveluch volcanoes. The concentrations of water and 20 trace elements were measured in the glasses of 22 melt inclusions in plagioclase and quartz from our samples. Unusually high values were obtained for Li concentrations (along with high Na concentrations) in the basaltic melts from the Karymskii volcanic center: from 118 to 1750 ppm, whereas the dacite and rhyolite melts contain 25 ppm Li on average. The rhyolite melts of Golovnina volcano are much poorer in Li: 1.4 ppm on average. The melts of the Karymskii volcanic center are characterized by relative minima at Nb and Ti and maxima at B and K, as is typical of arc magmas. 相似文献
272.
273.
An overview is presented on possible mechanisms that control the leaching behaviour of the oxyanion forming elements As, Cr, Mo, Sb, Se, V and W in cementituous systems and alkaline solid wastes, such as municipal solid waste incinerator bottom ash, fly ash and air pollution control residues, coal fly ash and metallurgical slags. Although the leachability of these elements generally depends on their redox state, speciation measurements are not common. Therefore, experimental observations available in the literature are combined with a summary of the thermal behaviour of these elements to assess possible redox states in freshly produced alkaline wastes, given their origin at high temperature. Possible redox reactions occurring at room temperature, on the other hand, are reviewed because these may alter the initial redox state in alkaline wastes and their leachates. In many cases, precipitation of oxyanions as a pure metalate cannot provide a satisfactory explanation for their leaching behaviour. It is therefore highly likely that adsorption and solid solution formation with common minerals in alkaline waste and cement reduce the leachate concentration of oxyanions below pure-phase solubility. 相似文献
274.
Regulatory authorities require estimates of ambient background concentrations (ABCs) of potentially harmful elements (PHEs) in topsoil; such data are currently not available in many countries. High resolution soil geochemical data exist for only part of England and Wales, whilst stream sediment data cover the entire landscape. A novel methodology is presented for estimating soil equivalent ABCs for PHEs from high-resolution (HR) stream sediment geochemical data grouped by common parent materials (PM), using arsenic (As) as an example. Geometric mean (GM) values for local PM groups are used to investigate different approaches for transforming sediment to soil equivalent concentrations. Holdout validation is used to assess: (i) the optimum number of samples for calculating local GM values, and (ii) the optimum scale at which to group data when using linear regression analysis to estimate GM soil ABCs from local sediment geochemical values. Holdout validation showed that the smallest differences were generally observed when five observations were used to calculate the GM and that these should be grouped over the smallest possible area in order to encompass soils over PMs with elevated GM As concentrations. Geometric mean ABCs are estimated and mapped for As in mineral soil across all of England and Wales within delineations of PM polygons. Errors for the estimation of soil equivalent GM As ABCs based on sediment data for an independent validation set were of a similar magnitude to those from holdout validation applied to the original data suggesting the approach is robust. The estimates of soil equivalent ABCs suggest that As exceeds the regulatory threshold used in risk assessments for residential land use (20 mg kg−1) across 16% of the landscape of England and Wales. The applicability of the method for cognate landscapes, and potential refinements is discussed. 相似文献
275.
276.
Corey Johnson 《GeoJournal》2008,72(1-2):75-89
As John Agnew (Political geography: a reader, 1997) has argued, political and economic change often occasions competing visions of the scales that are appropriate for organizing particular political and economic activities. Nowhere is this more evident than in the European Union, and eastern Germany offers compelling evidence of the contested nature of contemporary scalar politics. Yet a recent debate in human geography (see, e.g. Marston et al., Transactions of the Institute of British Geographers 30:416–432, 2005) calls into question the very concept of scale and rejects its hierarchical conceptualization. In light of this debate, it is appropriate to draw on real-world case studies to examine the ways in which geography figures into policy. Drawing on field work in Saxony, evidence is offered in the form of competing visions of regionalism in the EU context. The evidence presented complicates both hierarchical and flat notions of scale. The current process of querying space to identify those scales that are best-suited for the globalized economy offers insights into both the socially constructed nature of scale as well as the ways in which scalar lenses help to illuminate the geographical aspects (and consequences) of strategies for coping with structural changes. 相似文献
277.
M. Mejías J. Garcia-Orellana J. L. Plata M. Marina E. Garcia-Solsona B. Ballesteros P. Masqué J. López C. Fernández-Arrojo 《Environmental Geology》2008,54(3):521-536
A methodology for the characterization of deep carbonate aquifers has been developed and applied to El Maestrazgo Jurassic
aquifer in Castellón, Spain. Characterization of these aquifer formations, located at more than 300 m deep, consisted of a
previous phase of compilation, analysis and synthesis of the existing information about the area, followed by a coordinated
combination of different speciality studies: geology, stratigraphy, structural analysis, hydrogeology, hydrochemistry, geophysics
and remote sensing. Geological studies included geological mapping, definition of stratigraphical units and facies and structural
analysis. The aim of the hydrogeology study was to define aquifer formations, recharge area, aquifer points inventory and
groundwater flow directions for the establishment of piezometric and water quality observation nets. Special techniques were
applied, like thermal infrared aerial images and the evaluation of submarine groundwater discharge by means of natural radium
isotopes. Hydrochemical techniques, including majority elements characterization and stable isotopes (18O, 2H and 3H) determination, allowed classifying hydrochemical facies and establishing a renewal pattern for water within the system.
Geophysics was useful in determining the aquifer geometry, the features of the basement and the petrophysical characteristics
of the geological formations. Preliminary results show an important tectonic complexity and the possibilities for groundwater
uses in the area of study. 相似文献
278.
Two algorithms for in-situ detection and identification of vertical free convective and double-diffusive flows in groundwater
monitoring wells or boreholes are proposed. With one algorithm the causes (driving forces) and with the other one the effects
(convection or double-diffusion) of vertical transport processes can be detected based on geophysical borehole measurements
in the water column. Five density-driven flow processes are identified: thermal, solutal, and thermosolutal convection leading
to an equalization, as well as saltfingers and diffusive layering leading to an intensification of a vertical density gradient.
The occurrence of density-driven transport processes could be proven in many groundwater monitoring wells and boreholes; especially
shallow sections of boreholes or groundwater monitoring wells are affected dramatically by such vertical flows. Deep sections
are also impaired as the critical threshold for the onset of a density-driven flow is considerably low. In monitoring wells
or boreholes, several sections with different types of density-driven vertical flows may exist at the same time. Results from
experimental investigations in a medium-scale testing facility with high aspect ratio (height/radius = 19) and from numerical
modeling of a water column agree well with paramters of in-situ detected convection cells. 相似文献
279.
Implementation of reconstructed geomorphologic units in landslide susceptibility mapping: the Melen Gorge (NW Turkey) 总被引:6,自引:2,他引:4
In the international literature, although considerable amount of publications on the landslide susceptibility mapping exist,
geomorphology as a conditioning factor is still used in limited number of studies. Considering this factor, the purpose of
this article paper is to implement the geomorphologic parameters derived by reconstructed topography in landslide susceptibility
mapping. According to the method employed in this study, terrain is generalized by the contours passed through the convex
slopes of the valleys that were formed by fluvial erosion. Therefore, slope conditions before landsliding can be obtained.
The reconstructed morphometric and geomorphologic units are taken into account as a conditioning parameter when assessing
landslide susceptibility. Two different data, one of which is obtained from the reconstructed DEM, have been employed to produce
two landslide susceptibility maps. The binary logistic regression is used to develop landslide susceptibility maps for the
Melen Gorge in the Northwestern part of Turkey. Due to the high correct classification percentages and spatial effectiveness
of the maps, the landslide susceptibility map comprised the reconstructed morphometric parameters exhibits a better performance
than the other. Five different datasets are selected randomly to apply proper sampling strategy for training. As a consequence
of the analyses, the most proper outcomes are obtained from the dataset of the reconstructed topographical parameters and
geomorphologic units, and lithological variables that are implemented together. Correct classification percentage and root
mean square error (RMSE) values of the validation dataset are calculated as 86.28% and 0.35, respectively. Prediction capacity
of the different datasets reveal that the landslide susceptibility map obtained from the reconstructed parameters has a higher
prediction capacity than the other. Moreover, the landslide susceptibility map obtained from the reconstructed parameters
produces logical results. 相似文献
280.
B. Bühn 《Mineralogy and Petrology》2008,92(3-4):453-470
Summary Two bimodal carbonatite complexes in Namibia of Cretaceous age are explored as to the presence and composition of a coexisting
carbonatitic fluid. The Kalkfeld and Ondurakorume complexes contain both Ca- and Mg/Fe-carbonatites, composed of calcite alone
or calcite with ferroan dolomite, fluorapatite and strontianite. The major element evolution in the bulk rocks from s?vites
to beforsites is due to crystallization of calcite and fluorapatite. All carbonatites show a negative Y anomaly in normalised
REE plots. Fractionation is accompanied by successively lower HREE contents between Tb and Yb, expressed by the ratios Nd/Ho
and Ho/Lu. The evolution of this downward-facing hump goes along with decreasing Y contents in bulk rocks and minerals. All
this requires an additional phase coexisting with the carbonate liquid during fractionation. Comparison between the bulk rocks
and the expelled fluid shows that the latter had preferentially accumulated the HREE and Y. Further evidence for this process
are hydrothermal, HREE, Y-rich fluorites in other carbonatite complexes which reflect the composition of the expelled fluid.
The high strength of fluoride complexes suggests that fluoride complexing in the carbonatitic fluid is the process responsible
for extracting HREE and Y from the carbonatite magma, leaving fractionated carbonatite rocks depleted in these elements. The
geochemical evolution of carbonatite magmas along fractionation has therefore to be considered in a melt-mineral-fluid system.
Correspondence: B. Bühn, Instituto de Geociências, Universidade de Brasilia, Campus Universitário Darcy Ribeiro, Brasilia
70910-900, Brazil 相似文献