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181.
Márian Urban Rainer Thomas Vratislav Hurai Patrik Koneèný Martin Chovan 《Mineralium Deposita》2006,40(8):867-873
CO2 inclusions with density up to 1,197 kg m−3 occur in quartz–stibnite veins hosted in the low-grade Palaeozoic basement of the Gemericum tectonic unit in the Western Carpathians. Raman microanalysis corroborated CO2 as dominant gas species accompanied by small amounts of nitrogen (<7.3 mol%) and methane (<2.5 mol%). The superdense CO2 phase exsolved from an aqueous bulk fluid at temperatures of 183–237°C and pressures between 1.6 and 3.5 kbar, possibly up to 4.5 kbar. Low thermal gradients (∼12–13°C km−1) and the CO2–CH4–N2 fluid composition rule out a genetic link with the subjacent Permian granites and indicate an external, either metamorphogenic (oxidation of siderite, dedolomitization) or lower crustal/mantle, source of the ore-forming fluids.According to microprobe U–Pb–Th dating of monazite, the stibnite-bearing veins formed during early Cretaceous thrusting of the Gemeric basement over the adjacent Veporic unit. The 15- to 18-km depth of burial estimated from the fluid inclusion trapping PT parameters indicates a 8- to 11-km-thick Upper Palaeozoic–Jurassic accretionary complex overlying the Gemeric basement and its Permo-Triassic autochthonous cover. 相似文献
182.
E. M. Chamorro Pérez I. Daniel J.-C. Chervin P. Dumas J. D. Bass T. Inoue 《Physics and Chemistry of Minerals》2006,33(7):502-510
High-pressure synchrotron infrared (IR) absorption spectra were collected between 650 and 4,000 cm−1 at ambient temperature for hydrous Mg-ringwoodite (γ-Mg2SiO4) up to 30 GPa. The main feature in the OH− stretching region is an extremely broad band centred at 3,150 cm−1. The hydrogen bond is strong for most protons and the most probable site for protonation is the tetrahedral edge. With increasing pressure, this band shifts downward while decreasing its integrated intensity until disappearance at a pressure of 25 GPa. Only one band at 2,450 cm−1 and an absorption plateau persist with a maximum wavenumber of 3,800 cm−1. This behaviour is reversible upon pressure release. We interpret this as a second-order phase transition occurring in hydrated Mg-ringwoodite at high pressure (beyond ∼ 25 GPa). This result is compatible with the observation by Kleppe et al. (Phys Chem Miner 29:473–476, 2002a) who suggested the presence of Si–O–Si linkages and/or partial increase in the coordination of Si. Beyond the phase transition, the protons are delocalized and their environment on the ringwoodite structure is probably quite different from that at low pressure. Data obtained in situ at high pressures and temperatures are needed to better understand the effect of protonation on the structure and to better constrain this phase transition. 相似文献
183.
A two-dimensional global climate model is used to assessthe climatic changes associated with the new IPCC SRES emissions scenarios and to determine which kind of changes in total solar irradiance and volcanic perturbations could mask the projected anthropogenic global warming associated to the SRES scenarios. Our results suggest that only extremely unlikely changes in total solar irradiance and/or volcanic eruptions would be able to overcome the simulated anthropogenic global warming over the century. Nevertheless, in the critical interval of the next two decades the externally-driven natural climate variability might possibly confuse the debate about temperature trends and impede detection of the anthropogenic climate change signal. 相似文献
184.
In the cold Canadian environment, humidity measurements can be verydifficult to conduct. In this brief communication, humidity observationstaken by two different sensors at six remote Canadian Arctic locations arecompared. The observations collected by Vaisala HMP35CF sensors displaya strong tendency toward the ice saturation point whereas dew cell instrumentsexhibit significantly lower values of relative humidity with respect to ice (RHi).Humidity data collected by HMP35CF hygrometers are therefore unreliable sincethey are subject to persistent icing that lead them to record values of RHi near 100%, irrespective of the air temperature. The high humidity bias emerges atmeteorological stations mounted with the HMP35CF probes since these instrumentsare usually neither sheltered nor heated, and are not attended to at regular intervals. Thus, great care must be taken in utilizing humidity data recorded by HMP35CF sensors across the network of climate autostations in Canada. 相似文献
185.
In South Africa attempts are being made to address the socio-spatial distortions of the apartheid era through a more equitable
distribution of resources, and the re-drawing of municipal geographical boundaries. However, boundaries are not neutral geographic
lines. Boundary changes are often associated with a redistribution of political power and resources. The aim of this paper
is to analyse the effects of the contemporary territorial and administrative restructuring on urban dynamics in South Africa.
More specifically, the focus is on how the process of territorial restructuring impacted on metropolitan areas as well as
on secondary cities and their hinterlands. Examining and elucidating the manner in which various social, economic and political
forces have manifested themselves in the process of boundary delimitation in a major metropolitan centre as well as adjacent
rural areas is a central theme of this paper. There were considerable contestations over the delimitation of new local government
boundaries. Affluent metro authorities like that in Durban were opposed to the spatial extension of their boundaries because
of the costs of the providing services and infrastructure in the deprived margins. Similarly, there was concern that incorporation
of rural areas will result in increased municipal service charges being imposed on these communities. Tensions were heightened
between urban and rural regions because traditional leaders believed that their territorial jurisdiction and authority were
being undermined. In other parts of the country, the merger of traditionally white and black fragments of secondary cities
often resulted in many black locations continuing to be marginalized. There appears to be neither the political will nor the
economic capacity to upgrade these zones of marginalized urban communities. While the Municipal Demarcation Board was largely
successful in eliminating the political geography of apartheid at a macro- scale, this paper suggests that the greater challenge
for government and policy makers is to reduce the socio-spatial and economic inequalities which appears to be still very high
and perhaps increasing.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
186.
Groundwater-flow modeling in the Yucatan karstic aquifer, Mexico 总被引:1,自引:0,他引:1
Roger González-Herrera Ismael Sánchez-y-Pinto José Gamboa-Vargas 《Hydrogeology Journal》2002,10(5):539-552
The current conceptual model of the unconfined karstic aquifer in the Yucatan Peninsula, Mexico, is that a fresh-water lens
floats above denser saline water that penetrates more than 40 km inland. The transmissivity of the aquifer is very high so
the hydraulic gradient is very low, ranging from 7–10 mm/km through most of the northern part of the peninsula. The computer
modeling program AQUIFER was used to investigate the regional groundwater flow in the aquifer. The karstified zone was modeled
using the assumption that it acts hydraulically similar to a granular, porous medium. As part of the calibration, the following
hypotheses were tested: (1) karstic features play an important role in the groundwater-flow system; (2) a ring or belt of
sinkholes in the area is a manifestation of a zone of high transmissivity that facilitates the channeling of groundwater toward
the Gulf of Mexico; and (3) the geologic features in the southern part of Yucatan influence the groundwater-flow system. The
model shows that the Sierrita de Ticul fault, in the southwestern part of the study area, acts as a flow barrier and head
values decline toward the northeast. The modeling also shows that the regional flow-system dynamics have not been altered
despite the large number of pumping wells because the volume of water pumped is small compared with the volume of recharge,
and the well-developed karst system of the region has a very high hydraulic conductivity.
Electronic Publication 相似文献
187.
José F. Noguera Lluís Rivero Xavier Font Andrés Navarro Francisco Martínez 《Environmental Geology》2002,41(8):898-905
188.
189.
Victor Pinto Xavier Font Miquel Salgot Jose Tapias Tomas Mañá 《Environmental Geology》2002,41(5):495-503
One of the most important environmental impacts resulting from opencast mining, and especially quarries, is the visual impact. Evaluation of this impact considers two aspects: first, the area occupied by the quarry as seen by an observer from a specific place, and, second, the chromatic contrast existing between landscape and exploitation. In this study we develop a methodology to assess the chromatic impact in an objective and comparable form. To assess this impact we developed a method based on image analysis that allows us to obtain from a picture or image its equivalent as a function of chromatic impact, according to the sensibility of the human eye to different wavelengths. The methodology was applied to the Martinenca limestone quarry (Alcanar, Tarragona) and to Cerro Kori Kollo mine, La Joya district (Bolivia). 相似文献
190.
Several types of anhydrite-bearing rocks have been found in the amphibolite-facies metamorphosed rocks at the north-eastern margin of the Moldanubian Zone. Anhydrite either forms monomineralic bands up to 40 cm thick, or occurs in the form of disseminated grains in surrounding calc-silicate gneiss together with feldspar, scapolite, amphibole, pyroxene, epidote and pyrite. The isotopic composition of sulphur ('34S=30.6 to 32.3) and strontium (87Sr/86Sr=0.70797 to 0.70781) in anhydrite may indicate a marine source of sulphate. The isotopic ratio of strontium is in the same range as that of metamorphosed strata-bound barite-sulphide ores, which have been previously described in the same area. The '34S values of coexisting pyrite range from 21.4 to 22.5, the (34Sanhydrite-pyrite corresponding to the metamorphic temperature of 600 to 660 °C. In contrast to many submarine-exhalative deposits, the oxygen isotopic compositions of anhydrite ('18O=9.3 to 10.2) are lighter than that of barite ('18O=10.4 to 13.8). This indicates that the both minerals are not in isotopic equilibrium. Therefore, it is probable that anhydrite and barite from the Roná district were deposited from fluids that contained different proportions of seawater and hydrothermal fluids or from hydrothermal fluids that underwent variable extent of oxygen isotope exchange with seafloor rocks. The '13C values in calcite ('13C=-17.2 to -18.7) from anhydrite-bearing rock are lower than those in distant marbles. As graphite is absent in anhydrite- and calcite-bearing rocks, impoverishment in the 13C isotope cannot be attributed to the graphite-carbonate isotopic exchange during metamorphism. It is proposed that low '13C values in carbonates are caused by pre-metamorphic oxidation of organic matter in course of hydrothermal processes. Anhydrite and anhydrite-bearing calc-silicate gneiss from the north-eastern part of the Moldanubian Zone are interpreted to be the high-grade metamorphosed analogue of anhydrite-rich exhalites commonly found in submarine-exhalative hydrothermal deposits. 相似文献