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101.
In this paper, the process of oasis-desert circulation (ODC) is simulated by MM5V3.5 model through designing an ideal oasis-desert scheme and assuming that initial atmosphere is at rest (V = 0). The findings showed that the key of forming special oasis boundary structure is the difference of energy and water between oasis and desert. The evaporation of oasis surface consumes heat energy, and the low temperature of oasis causes an oasis breeze circulation (OBC), which drives an ODC with a downdraft over the oasis and an updraft over the desert. Later, the cold, dry and stable boundary over oasis is gradually formed, on the contrary,the atmospheric boundary over desert on the edge of oasis is hot, humid and unstable and its height is about 600 hPa. The updraft over the desert forms a wet ring that acts as a vertical wall weakening the low-level moisture exchange between the oasis and desert. The downdraft of OBC increases the atmospheric stability that reduces the oasis evaporation. The low-level outflow from the oasis (into the desert) prevents the dry, hot air flowing from the desert into the oasis.Thus an oasis self-preservation mechanism may be formed due to OBC. The horizontal area influenced by oasis is twice as oasis area and the vertical range is four times as oasis. The ODC is strong in the daytime and reaches the strongest at 17:00, and the influenced area is the largest at 20:00. 相似文献
102.
Ambiguous Moment Tensors and Radiation Patterns in Anisotropic Media with Applications to the Modeling of Earthquake Mechanisms in W-Bohemia 总被引:3,自引:0,他引:3
Anisotropic material properties are usually neglected during inversions for source parameters of earthquakes. In general anisotropic media, however, moment tensors for pure-shear sources can exhibit significant non-double-couple components. Such effects may be erroneously interpreted as an indication for volumetric changes at the source. Here we investigate effects of anisotropy on seismic moment tensors and radiation patterns for pure-shear and tensile-type sources. Anisotropy can significantly influence the interpretation of the source mechanisms. For example, the orientation of the slip within the fault plane may affect the total seismic moment. Also, moment tensors due to pure-shear and tensile faulting can have similar characteristics depending on the orientation of the elastic tensor. Furthermore, the tensile nature of an earthquake can be obscured by near-source anisotropic properties. As an application, we consider effects of inhomogeneous anisotropic properties on the seismic moment tensor and the radiation patterns of a selected type of micro-earthquakes observed in W-Bohemia. The combined effects of near-source and along-path anisotropy cause characteristic amplitude distortions of the P, S1 and S2 waves. However, the modeling suggests that neither homogeneous nor inhomogeneous anisotropic properties alone can explain the observed large non-double-couple components.The results also indicate that a correct analysis of the source mechanism, in principle, is achievable by application of anisotropic moment tensor inversion. 相似文献
103.
104.
105.
Harald Behrens Susanne Ohlhorst Michel Champenois 《Geochimica et cosmochimica acta》2004,68(22):4687-4703
The solubility of CO2 in dacitic melts equilibrated with H2O-CO2 fluids was experimentally investigated at 1250°C and 100 to 500 MPa. CO2 is dissolved in dacitic glasses as molecular CO2 and carbonate. The quantification of total CO2 in the glasses by mid-infrared (MIR) spectroscopy is difficult because the weak carbonate bands at 1430 and 1530 cm−1 can not be reliably separated from background features in the spectra. Furthermore, the ratio of CO2,mol/carbonate in the quenched glasses strongly decreases with increasing water content. Due to the difficulties in quantifying CO2 species concentrations from the MIR spectra we have measured total CO2 contents of dacitic glasses by secondary ion mass spectrometry (SIMS).At all pressures, the dependence of CO2 solubility in dacitic melts on xfluidCO2,total shows a strong positive deviation from linearity with almost constant CO2 solubility at xCO2fluid > 0.8 (maximum CO2 solubility of 795 ± 41, 1376 ± 73 and 2949 ± 166 ppm at 100, 200 and 500 MPa, respectively), indicating that dissolved water strongly enhances the solubility of CO2. A similar nonlinear variation of CO2 solubility with xCO2fluid has been observed for rhyolitic melts in which carbon dioxide is incorporated exclusively as molecular CO2 (Tamic et al., 2001). We infer that water species in the melt do not only stabilize carbonate groups as has been suggested earlier but also CO2 molecules.A thermodynamic model describing the dependence of the CO2 solubility in hydrous rhyolitic and dacitic melts on T, P, fCO2 and the mol fraction of water in the melt (xwater) has been developed. An exponential variation of the equilibrium constant K1 with xwater is proposed to account for the nonlinear dependence of xCO2,totalmelt on xCO2fluid. The model reproduces the CO2 solubility data for dacitic melts within ±14% relative and the data for rhyolitic melts within 10% relative in the pressure range 100-500 MPa (except for six outliers at low xCO2fluid). Data obtained for rhyolitic melts at 75 MPa and 850°C show a stronger deviation from the model, suggesting a change in the solubility behavior of CO2 at low pressures (a Henrian behavior of the CO2 solubility is observed at low pressure and low H2O concentrations in the melt). We recommend to use our model only in the pressure range 100-500 MPa and in the xCO2fluid range 0.1-0.95. The thermodynamic modeling indicates that the partial molar volume of total CO2 is much lower in rhyolitic melts (31.7 cm3/mol) than in dacitic melts (46.6 cm3/mol). The dissolution enthalpy for CO2 in hydrous rhyolitic melts was found to be negligible. This result suggests that temperature is of minor importance for CO2 solubility in silicic melts. 相似文献
106.
The impact of hydrological changes on travertine deposits related to thermal springs in the Pamukkale area (SW Turkey) 总被引:2,自引:0,他引:2
Dilsiz Cüneyt Marques José Manuel Carreira Paula Maria Mimo 《Environmental Geology》2004,45(6):808-817
Pamukkale thermal waters (35 °C), exhibiting calcium-bicarbonate-sulfate composition and high carbon dioxide concentration, are of a predominantly meteoric origin. The meteoric fluid, circulating through faults and fractures, is heated by magmatic intrusions at great depth, and ascends from deep reservoirs to the surface. Mixing with relatively cold groundwater in the near surface zone promotes different saturation conditions with respect to calcium carbonate that later precipitates at depth and/or the surface. Dissolution-deposition processes of calcium carbonate both at surface and depth environments may help to reconstruct past climate direction in the field. During wet climate conditions a high-rate of calcium carbonate accumulation would be expected to occur at the surface because thermal fluid would be under-saturated with respect to calcium carbonate at depth because of a relatively higher mixing ratio with cold groundwater. During dry climate conditions the thermal fluid would be super-saturated at depth because of the highly acidic environment. Hydrometeorological studies reveal that the annual precipitation at the Pamukkale hydrothermal field tends to decrease with time. This climatic change in the area was also detected from geological records. While humid climate conditions prevailed during the late Quaternary, the area has recently been affected by arid/semi-arid climate conditions, followed by some episodic transitions. This study has shown how the system has possibly reacted to different climate conditions since antiquity. 相似文献
107.
Hege Fonneland-Jorgensen Harald Furnes Karlis Muehlenbachs Yildirim Dilek 《Island Arc》2005,14(4):517-541
Abstract The Solund‐Stavfjord ophiolite complex (SSOC) in western Norway represents a remnant of the Late Ordovician oceanic lithosphere, which developed in an intermediate‐ to fast‐spreading Caledonian back‐arc basin. The internal architecture and magmatic features of its crustal component suggest that the SSOC has a complex, multistage sea floor spreading history in a supra‐subduction zone environment. The youngest crustal section associated with the propagating rift tectonics consists of a relatively complete ophiolite pseudostratigraphy, including basaltic volcanic rocks, a transition zone between the sheeted dyke complex and the extrusive sequence, sheeted dykes, and high‐level isotropic gabbros. Large‐scale variations in major and trace element distributions indicate significant remobilization far beyond that which would result from magmatic processes, as a result of the hydrothermal alteration of crustal rocks. Whereas K2O is strongly enriched in volcanic rocks of the extrusive sequence, Cu and Zn show the largest enrichment in the dyke complex near the dyke–volcanic transition zone or within this transition zone. The δ18O values of the whole‐rock samples show a general depletion structurally downwards in the ophiolite, with the largest and smallest variations observed in volcanic rocks and the transition zone, respectively. δ18O values of epidote–quartz mineral pairs indicate 260–290°C for volcanic rocks, 420°C for the transition zone, 280–345°C for the sheeted dyke complex and 290–475°C for the gabbros. The 87Sr/86Sr isotope ratios show the widest range and highest values in the extrusive rocks (0.70316–0.70495), and generally the lowest values and the narrowest range in the sheeted dyke complex (0.70338–0.70377). The minimum water/rock ratios calculated show the largest variations in volcanic rocks and gabbros (approximately 0–14), and generally the lowest values and range in the sheeted dyke complex (approximately 1–3). The δD values of epidote (?1 to ?12‰), together with the δ18O calculated for Ordovician seawater, are similar to those of present‐day seawater. Volcanic rocks experienced both cold and warm water circulation, resulting in the observed K2O‐enrichment and the largest scatter in the δ18O values. As a result of metal leaching in the hot reaction zone above a magma chamber, Zn is strongly depleted in the gabbros but enriched in the sheeted dyke complex because of precipitation from upwelling of discharged hydrothermal fluids. The present study demonstrates that the near intact effect of ocean floor hydrothermal activity is preserved in the upper part of the SSOC crust, despite the influence of regional lower greenschist facies metamorphism. 相似文献
108.
Sustaining the human ecological benefits of surface water requires carefully planned strategies for reducing the cumulative
risks posed by diverse human activities. Municipal governments in Aksaray City play a key role in developing solutions to
surface water management and protection problems. The responsibility to provide drinking water and sewage works, regulate
the use of private land, and protect public health provides the mandate and authority to take action. A large part of Aksaray
City uses Mamasın dam water as its primary source for drinking water. Several point sources of contamination may result from
direct wastewater discharges from Melendiz and Karasu rivers, which recharge the Mamasın dam watershed. Relevant studies were
carried out for monitoring the eutrophication process, which usually occurs in the static water mass of the Mamasın dam lake.
This process may be caused by the continual increase in nutrients and decrease of O2 levels, causing anaerobic conditions. Stimulated algae growth in these water bodies consequently reduces water quality. Hydrochemical
parameters were evaluated to estimate the types of pollution sources, the level of pollution, and its environmental impacts
on the Mamasın dam drinking water reservoir. 相似文献
109.
110.
M. Koch-Müller P. Dera Y. Fei H. Hellwig Z. Liu J. Van Orman R. Wirth 《Physics and Chemistry of Minerals》2005,32(5-6):349-361
We synthesized superhydrous phase B (shy-B) at 22 GPa and two different temperatures: 1200°C (LT) and 1400°C (HT) using a
multi-anvil apparatus. The samples were investigated by transmission electron microscopy (TEM), single crystal X-ray diffraction,
Raman and IR spectroscopy. The IR spectra were collected on polycrystalline thin-films and single crystals using synchrotron
radiation, as well as a conventional IR source at ambient conditions and in situ at various pressures (up to 15 GPa) and temperatures
(down to −180°C). Our studies show that shy-B exists in two polymorphic forms. As expected from crystal chemistry, the LT
polymorph crystallizes in a lower symmetry space group (Pnn2), whereas the HT polymorph assumes a higher symmetry space group (Pnnm). TEM shows that both modifications consist of nearly perfect crystals with almost no lattice defects or inclusions of additional
phases. IR spectra taken on polycrystalline thin films exhibit just one symmetric OH band and 29 lattice modes for the HT
polymorph in contrast to two intense but asymmetric OH stretching bands and at least 48 lattice modes for the LT sample. The
IR spectra differ not only in the number of bands, but also in the response of the bands to changes in pressure. The pressure
derivatives for the IR bands are higher for the HT polymorph indicating that the high symmetry form is more compressible than
the low symmetry form. Polarized, low-temperature single-crystal IR spectra indicate that in the LT-polymorph extensive ordering
occurs not only at the Mg sites but also at the hydrogen sites. 相似文献