首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
The removal of benzene, toluene, ethylbenzene, and xylene (BTEX) from aqueous solution by multi- and single-walled carbon nanotubes (MWCNTs and SWCNTs), hybrid carbon nanotubes (HCNTs) and nano-Fe was evaluated for a nanomaterials dose of 1 g/L and a BTEX concentration of 10 mg/L and pH 7. The equilibrium amount (q e ) (mg/g) removed by SWCNTs (B: 9.98, T: 9.96, E: 9.97, and X: 9.97 mg/g) was higher than for MWCNTs, HCNTs and nano-Fe in a c 0 of 10 mg/L and for a contact time of 10 min. The q e of total BTEX removed via SWCNTs was 39.89 mg/g. The order of uptake for SWCNTs is X > T = E > B, which is related to the increasing water solubility and the decreasing molecular weight of the compounds. The SWCNTs performed better for BTEX sorption than the MWCNTs, HCNTs and nano-Fe. The results of desorption study show that BTEX adsorbed on SWCNTs can easily be desorbed at 105 ± 2°C. It was concluded that recycling CNTs using heat improved the performance of the CNTs. For the first time, better adsorption performance was observed for recycled CNTs than for raw CNTs. SWCNTs are efficient BTEX adsorbents that could be used for cleaning up environmental pollution.  相似文献   

2.
Liu X  Xu L  Sun L  Liu F  Wang Y  Yan H  Liu Y  Luo Y  Huang J 《Marine pollution bulletin》2011,62(10):2205-2212
We reconstructed the first long-term (∼400 years) records of black carbon (BC) deposition flux from three ornithogenic sediment profiles, which were collected from three remote, isolated islets of the Xisha archipelago, South China Sea. The significant correlations between black carbon, organic matter and excess 210Pb suggested that black carbon was mainly derived from atmospheric deposition, and further enriched by plant-derived organic matter in sediments. During the past 400 years, the BC flux remained relatively low before the onset of 20th century; it started to increase from approximately 1900 AD, and peaked around the 1970s. In the recent 30 years, the BC flux seemed to display decreasing trend, very likely due to the change of energy structure and development of pollution control techniques. In comparison with marginal sea regions that are greatly impacted by anthropogenic activities, these pristine Xisha islands were not significantly influenced by black carbon of anthropogenic origin.  相似文献   

3.
Accumulation rates of marine and terrigenous organic carbon in the continental margin sediments off southwestern Taiwan were estimated from the measured concentrations and isotopic compositions of total organic carbon (TOC) and previously reported sedimentation rates. Surficial sediments were collected from the study area spanning from the narrow shelf near the Kaoping River mouth to the deep slope with depths reaching almost 3000 m. The average sediment loading of Kaoping River is 17 Mt/yr, which yields high sediment accumulation rates ranging from 0.08 to 1.44 g cm−2 yr−1 in the continental margin. About half of the discharged sediments were deposited on the margin within 120 km of the river mouth. Carbon isotopic compositions of terrestrial and marine end-members of organic matter were determined, respectively, based on suspended particulate matter (SPM) collected from three major rivers in the southwestern Taiwan and from an offshore station. All samples were analyzed for the TOC content and its isotopic composition (δ13Corg). The SPM samples were also analyzed for the total nitrogen (TN) content. TOC content in marine sediments ranges from 0.45% to 1.35% with the highest values on the upper slope near the Kaoping River mouth. The TOC/TN ratio of the SPM samples from the offshore station is 6.8±0.6, almost identical to the Redfield ratio, indicating their predominantly marine origin; their δ13Corg values are also typically marine with a mean of −21.5±0.3‰. The riverine SPM samples exhibit typical terrestrial δ13Corg values around −25‰. The δ13Corg values of surficial sediments range from −24.8‰ to −21.2‰, showing a distribution pattern influenced by inputs from the Kaoping River. The relative contributions from marine and terrestrial sources to sedimentary organic carbon were determined by the isotope mixing model with end-member compositions derived from the riverine and marine SPM. High fluvial sediment inputs lead to efficient trapping of organic carbon over a wide range of water depth in this continental margin. The marine organic accumulation rate ranges from 1.6 to 70 g C m−2 yr−1 with an area weighted mean of 4.2 g C m−2 yr−1, which is on a par with the mean terrestrial contribution and accounts for 2.3% of mean primary production. The depth-dependent accumulation rate of marine organic carbon can be simulated with a function involving primary productivity and mineral accumulation rate, which may be applicable to other continental margins with high sedimentation rates. Away from the nearshore area, the content of terrigenous organic carbon in surficial sediments decreases with distance from the river mouth, indicating its degradation in marine environments.  相似文献   

4.
Biodegradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated sediment is an attractive remediation technique and its success depends on biodegradation kinetics, and the optimal condition for the PAH-degrading isolates; however, information on this aspect is still scarce. The effects of multi-factors on biodegradation of phenanthrene, a 3-ring model PAH, in contaminated sediment slurry by Sphingomonas sp. a bacterial strain isolated from surface mangrove sediment, were investigated using the orthogonal experimental design (form L16(45)). The most significant factors were salinity and inoculum size, while the effects of phenanthrene concentrations, nutrient addition and temperatures were insignificant. The optimal biodegradation condition in contaminated mangrove sediment slurry was 30 °C, 15 ppt salinity, a carbon/nitrogen ratio of 100:1 (the background ratio in sediment) and an inoculum size of 106 most probable number g−1 sediment. The phenanthrene biodegradation could be best described by the first order rate model, C = C0e−kt, where k (the rate constant) is equaled to 0.1185, under the optimal condition. The kinetic model was verified and its validity in predicting biodegradation by Sphingomonas sp. at various phenanthrene concentrations was proved by experimental data.  相似文献   

5.
《Marine pollution bulletin》2012,64(5-12):523-527
Concentrations of trace metals (Zn, Cr, Cu, V, Cd and Pb), total organic carbon (TOC), black carbon (BC) and their granulometry were examined in 25 surface sediment samples from the northern Bering Sea, Chukchi Sea and adjacent areas. Trace metal concentrations in the sediments varied from 21.06–168.21 mg kg−1 for Zn, 8.91–46.94 mg kg−1 for Cr, 2.69–49.39 mg kg−1 for Cu, 32.46–185.54 mg kg−1 for V, 0.09–0.92 mg kg−1 for Cd, and 0.95–15.25 mg kg−1 for Pb. The geoaccumulation index (Igeo) indicated that trace metal contamination (Zn and Cd) existed in some stations of the study area. The distribution of grain size plays an important role in influencing the distribution of trace metals (Zn, Cr, Cu, V, and Pb) in sediments from the Chukchi Sea and adjacent areas.  相似文献   

6.
This paper describes the GPS applicability for detecting the vertical displacements of ground stations caused by ocean tide loading effects. An experiment was carried out using 12 permanent GPS stations located in the coastal area of Korea using data in the period 1 July until 26 August 2003. The relative height differences were calculated from hourly DGPS data processing based on the carrier-phase observation. The power spectra of the M2 and N2 constituents of ocean tide loading were derived using the CLEAN algorithm. The differential vertical displacements generated by the ocean tide loading effect are typically 3–25 mm in coastal area of the Korea. We compared the results from GPS with those of the ocean tide models, NAO.99Jb regional model and GOT00.2, FES99 global models. The M2 (N2) amplitude differences of vertical displacements between GPS and GOT00.2 is 1.22 ± 3.61 mm (1.01 ± 1.48 mm), and that of the M2 (N2) amplitude difference between GPS and FES99 is 0.04 ± 4.64 mm (0.64 ± 1.75 mm), whereas the M2 (N2) amplitude difference between GPS and NAO.99Jb are 0.05 ± 1.03 mm (0.86 ± 1.18 mm). The highest vertical displacements at the PALM station are found for 24.5 ± 0.7 mm from GPS observation, and 22.9 mm from the regional model NAO.99Jb and 13.17 and 10.00 mm from the global models GOT00.2 and FES99, respectively. These values show that the vertical displacements derived from GPS are in good agreement with those of the regional model NAO.99Jb around Korea, more than with the global models. This result indicated that GPS is an effective tool to measure the vertical displacement caused by the ocean tide loading effect in the coastal area, and we need to use the NAO.99Jb ocean tide model rather than the global ocean tide models in and around the Korean peninsula for position determination with permanent GPS installations. This work demonstrates that vertical displacement caused by the M2 and N2 constituents of ocean tide loading can be measured by carrier-phase DGPS.  相似文献   

7.
Surface partial pressure of CO2 (pCO2), temperature, salinity, nutrients, and chlorophyll a were measured in the East China Sea (ECS; 31°30′–34°00′N to 124°00′–127°30′E) in August 2003 (summer), May 2004 (spring), October 2004 (early fall), and November 2005 (fall). The warm and saline Tsushima Warm Current was observed in the eastern part of the survey area during four cruises, and relatively low salinity waters due to outflow from the Changjiang (Yangtze River) were observed over the western part of the survey area. Surface pCO2 ranged from 236 to 445 μatm in spring and summer, and from 326 to 517 μatm in fall. Large pCO2 (values >400 μatm) occurred in the western part of the study area in spring and fall, and in the eastern part in summer. A positive linear correlation existed between surface pCO2 and temperature in the eastern part of the study area, where the Tsushima Warm Current dominates; this correlation suggests that temperature is the major factor controlling surface pCO2 distribution in that area. In the western part of the study area, however, the main controlling factor is different and seasonally complex. There is large transport in this region of Changjiang Diluted Water in summer, causing low salinity and low pCO2 values. The relationship between surface pCO2 and water stability suggests that the amount of mixing and/or upwelling of CO2-rich water might be the important process controlling surface pCO2 levels during spring and fall in this shallow region. Sea–air CO2 flux, based on the application of a Wanninkhof [1992. Relationship between wind speed and gas exchange over the ocean. Journal of Geophysical Research 97, 7373–7382] formula for gas transfer velocity and a set of monthly averaged satellite wind data, were −5.04±1.59, −2.52±1.81, 1.71±2.87, and 0.39±0.18 mmol m−2 d−1 in spring, summer, early fall, and fall, respectively, in the northern ECS. The ocean in this study area is therefore a carbon sink in spring and summer, but a weak source or in equilibrium with the atmosphere in fall. If the winter flux value is assumed to have been the mean of autumnal and vernal values, then the northern ECS absorbs about 0.013 Pg C annually. That result suggests that the northern ECS is a net sink for atmospheric CO2, a result consistent with previous studies.  相似文献   

8.
Shallow groundwater temperature response to climate change and urbanization   总被引：4，自引：0，他引：4  
Groundwater temperatures, especially in shallow (quaternary) aquifers respond to ground surface temperatures which in turn depend on climate and land use. Groundwater temperatures, therefore, are modified by climate change and urban development. In northern temperate climate regions seasonal temperature cycles penetrate the ground to depths on the order of 10–15 m. In this paper, we develop and apply analytic heat transfer relationships for 1-D unsteady effective diffusion of heat through an unsaturated zone into a flowing aquifer a short distance below the ground surface. We estimate how changes in land use (urban development) and climate change may affect shallow groundwater temperatures. We consider both long-term trends and seasonal cycles in surface temperature changes. Our analysis indicates that a fully urbanized downtown area at the latitude of Minneapolis/St. Paul is likely to have a groundwater temperature that is nearly 3 °C warmer than an undeveloped agricultural area at the same geographic location. Pavements are the main cause of this change. Data collected by the Minnesota Pollution Control Agency (MPCA) in the St. Cloud, MN area confirm that land use influences groundwater temperatures. Ground surface temperatures are also projected to rise in response to global warming. In the extreme case of a doubling of atmospheric carbon dioxide (2 × CO2 climate scenario), groundwater temperatures in the Minneapolis/St. Paul metropolitan area could therefore rise by up to 4 °C. Compounding a land use change from “undeveloped” to “fully urbanized” and a 2 × CO2 climate scenario, groundwater temperatures are projected to rise by about 5 °C at the latitude of Minneapolis/St. Paul.  相似文献   

9.
The climatic and environmental effects of atmospheric aerosols are a hot topic in global science community, and radiative properties of the aerosols are one of the important parameters in assessing climatic change. Here we studied the black carbon concentration and absorption coefficient measured with aethalometers, scattering coefficient measured with nephelometers, and single scattering albedo derived at an atmospheric composition watch station in Guangzhou from 2004 to 2007. Our main results are as follows. The data of black carbon concentration and absorption coefficients measured with instruments cannot be directly used until they are measured in parallel with internationally accepted instruments for comparison, calibration, and reduction. After evaluation of the data, the result shows that the monthly mean of BC concentration varies 3.1–14.8 μg·m−3 and the concentration decreases by about 1 μg·m−3 in average over the four years; It is higher in the dry season with a multi-year mean of 8.9 μg/m3 and lower in the rainy season with a multi-year mean of 8.0 μg·m−3; The extreme maximum of monthly mean concentration occurred in December 2004 and extreme minimum in July 2007, and a 4-year mean is 8.4 μg·m−3. It is also shown that monthly mean scattering coefficient derived varies 129 −565 Mm−1, monthly mean absorption coefficient 32–139 Mm−1, and monthly mean single scattering albedo 0.71–0.91, with annual mean values of 0.80, 0.82, 0.79 and 0.84 for 2004, 2005, 2006 and 2007, respectively. Three instruments were used to take simultaneous measurements of BC in PM10, PM2.5, and PM1 and the results showed that PM2.5 took up about 90% of PM10 and PM1 accounted for about 68% of PM2.5, and BC aerosols are mainly present in fine particulates. The variability of BC concentrations is quite consistent between the Nancun station (141 m above sea level) and the Panyu station (13 m above sea level), which are 8 km apart from each other. The concentration in higher altitude station (Panyu) is consistently lower than the lower altitude station (Nancun), and the difference of annual mean is about 4 μg·m−3. Supported by Natural Science Foundation of China (Grant Nos. U0733004, 40375002, 40418008, 40775011), National High Technology R & D Program of China (Grant Nos. 2006AA06A306 and 2006AA06A308) and National Basic Research Program of China (Grant No. 2005CB422207)  相似文献   

10.
Samples of the Dhajala H3.8 chondrite have been annealed for 10 hours at 600, 700, 800, 900 and 1000°C and at 1000°C for 1, 2, 20 and 100 h and their thermoluminescence (TL) properties measured. The TL sensitivity decreased by a factor of 2 after annealing at < 900°, but at higher temperatures fell by an order of magnitude. An abrupt increase in the temperature of the TL peak from 172 ± 9°Cto231 ± 8°C and a steady increase in the width of the peak from 169 ± 7°Cto212 ± 5°C were caused by the annealing treatment. The TL phosphor in Dhajala is thought to be feldspar predominantly in the high-temperature (disordered) form, but the present data indicate that a contribution from the low-temperature form is also present and that this low-temperature component is converted to the high form by the annealing treatment. The low-temperature feldspar is located in a few of the chondrules ( 20% of those separated from the meteorite) which are also noteworthy for having high TL sensitivities. These chondrules must have suffered greater crystallization of their mesostasis than the other chondrules, and equilibrated to lower temperatures. It is argued that, for compositional reasons, their mesostasis constituted less of a barrier to diffusion and therefore equilibration. Presumably the post-metamorphic cooling rate of the meteorite through the stability field of the low form was slow enough to permit some crystallization, and the width and temperature of the TL peaks for petrologic types 3.5–3.9 are somehow related to cooling rate. Based on TL, there is no indication of a correlation between petrologic type and cooling rate for types 3.5–3.9; this is not consistent with a simple, single internally heated meteorite parent body.  相似文献   

11.
Since 2000, 18 High Asia glaciers have been surveyed for black carbon (BC) deposition 22 times, and numerous snow samples and ice cores have been collected by researchers. However, most of the results were interpreted individually in papers. Here, we assemble the data and discuss the distribution of BC deposition and its impacts on the melting of the glaciers through radiative forcing. We find that BC distribution on the surfaces of High Asia glaciers primarily depends upon their elevations (i.e., higher sites have lower concentrations) and then upon regional BC emissions and surface melting conditions. BC concentrations in High Asia glaciers are similar to the Arctic and western American mountains but are significantly less than heavy industrialized areas such as northern China. Although Himalayan glaciers, which are important due to their water resources, are directly facing the strong emissions from South Asia, their mean BC is the lowest due to high elevations. A new finding indicated by ice core records suggested that great valleys in the eastern Himalayan section are effective pathways for BC entering the Tibetan Plateau and make increasing BC trends in the local glaciers. On average, BC deposition causes a mean forcing of ∼6 W m−2 (roughly estimated 5% of the total forcing) in High Asia glaciers and therefore may not be a major factor impacting the melting of most glaciers.  相似文献   

12.
The Dixon Island Formation of the coastal Pilbara Terrane, Western Australia is a 3.2 Ga volcanic–sedimentary sequence influenced by syndepositional hydrothermal activity formed in an island‐arc setting. We documented lateral variations in stratigraphy, hydrothermal alteration, and biological activity recorded in the sedimentary rocks (over several kilometers), with the aim of identifying areas of biological activity and related small‐scale structures. The Dixon Island Formation comprises volcaniclastics, black chert, and iron‐rich chert within seven tectonic blocks. Based on detailed geological mapping, stratigraphic columns, carbon isotope composition, and organic carbon (Corg) content, we found lateral (>5 km) variations in stratigraphy and carbon isotope compositions in a black chert sequence above the Mesoarchean seafloor with hydrothermal activity. Two felsic tuff layers are used as stratigraphic marker beds within a black chert sequence, which was deposited on altered volcanic rocks. The black chert sequence in each tectonic block is 10–20 m thick. Thickness variations reflect topographical undulations in the paleo‐ocean floor due to faulting. Early‐stage normal faults indicate extensional conditions after hydrothermal activity. Black chert beds in the topographically subsided area contain higher Corg contents (about 0.4 wt%) than in areas around the depression (<0.1 wt%). Carbon isotope compositions for the black chert vary from ?40 to ?25‰, which are similar to values obtained for a black chert vein within the komatiite–rhyolite tuff sequence (underlying the black chert sequence). Those for other rock types in the Dixon Island Formation are ?33 to ?15‰. Results indicate that deformation occurred soon after the final stages of hydrothermal activity. After this early‐stage deformation, organic‐rich sediments were deposited over an area several kilometers across. The organic‐rich sediments indicate stagnant anoxic conditions that resulted in the deposition of siliceous and organic matter from hydrothermal vein systems. When hydrothermal activity terminated, normal faulting occurred and organic matter was deposited from the sea surface and silica from the seafloor.  相似文献   

13.
Cirque-wall exposures of cone-forming deposits of Pleistocene Broken Top volcano, Oregon Cascade Range, reveal that the volcano is composed of unconformity-bounded constructional units of coherent lava (lava-flow cores) and breccia. Coarse-grained autoclastic breccias are found above and below lava-flow cores and may extend downslope from coherent lava outcrops where they may or may not be associated with thin lava stringers. Mantle-bedded scoria-fall breccias are recognized by generally good sorting, mantle bedding, and presence of aerodynamically shaped bombs. These breccias vary considerably in thermal oxidation coloration (black, red, orange, purple). Many breccia layers are unsorted mixtures of scoria and lithic (nonvesicular) fragments that grade laterally to unambiguous autoclastic breccia or lava-flow cores. These layers are interpreted as hybrid pyroclastic–autoclastic deposits produced by incorporation of falling or fallen tephra into advancing lava-flow fronts. This latter breccia type is common at Broken Top and offers particular challenges for clast or deposit classification.Progressive thermal demagnetization results for selected examples of different breccia types show that most scoria-fall and autoclastic breccias are emplaced at elevated temperatures (averaging 100–300°C). Clasts within single deposits record different emplacement temperatures ranging, in some cases, from 100 to over 580°C indicating a lack of thermal equilibration within deposits. Magnetization directions for single breccia deposits are more dispersed than data typically reported for lava flows. Settling and rotation of clasts after cooling or incorporation of colder clasts that are not significantly reheated probably accounts for the relatively high dispersion and suggests that paleomagnetic studies demanding low within-site dispersion (e.g., for determining paleomagnetic poles or evaluating tectonic rotation) should avoid volcanic breccias.  相似文献   

14.
Pressure–volume–temperature relations have been measured to 32 GPa and 2073 K for natural magnesite (Mg0.975Fe0.015Mn0.006Ca0.004CO3) using synchrotron X-ray diffraction with a multianvil apparatus at the SPring-8 facility. A least-squares fit of the room-temperature compression data to a third-order Birch–Murnaghan equation of state (EOS) yielded K0 = 97.1 ± 0.5 GPa and K′ = 5.44 ± 0.07, with fixed V0 = 279.55 ± 0.02 Å3. Further analysis of the high-temperature compression data yielded the temperature derivative of the bulk modulus (∂KT/∂T)P = −0.013 ± 0.001 GPa/K and zero-pressure thermal expansion α = a0 + a1T with a0 = 4.03 (7) × 10−5 K−1 and a1 = 0.49 (10) × 10−8 K−2. The Anderson–Grüneisen parameter is estimated to be δT = 3.3. The analysis of axial compressibility and thermal expansivity indicates that the c-axis is over three times more compressible (KTc = 47 ± 1 GPa) than the a-axis (KTc = 157 ± 1 GPa), whereas the thermal expansion of the c-axis (a0 = 6.8 (2) × 10−5 K−1 and a1 = 2.2 (4) × 10−8 K−2) is greater than that of the a-axis (a0 = 2.7 (4) × 10−5 K−1 and a1 = −0.2 (2) × 10−8 K−2). The present thermal EOS enables us to accurately calculate the density of magnesite to the deep mantle conditions. Decarbonation of a subducting oceanic crust containing 2 wt.% magnesite would result in a 0.6% density reduction at 30 GPa and 1273 K. Using the new EOS parameters we performed thermodynamic calculations for magnesite decarbonation reactions at pressures to 20 GPa. We also estimated stability of magnesite-bearing assemblages in the lower mantle.  相似文献   

15.
The Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ13Corg) and sulfur isotopes (δ34S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ13Corg (?36 ‰ to ?27 ‰) and δ34S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of < 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.  相似文献   

16.
Single-crystal elasticity of stishovite was examined using a new experimental technique and an empirical macroscopic model. Employing high-frequency resonant ultrasound spectroscopy, single-crystal elastic constants of stishovite were determined: C11 = 443(3), C33 = 781(4), C12 = 193(2), C23 = 199(2), C44 = 256(2), and C33 = 316(2) GPa. The frequency range of the resonant ultrasound spectroscopy techniques was 6–20 MHz, which is much lower than the ～10 GHz range of the Brillouin scattering technique. Of the elastic constants, the shear elastic constants C44 and C66 are consistent with the average value of the previously mentioned Brillouin scattering. Conversely, the four elastic constants, C11, C33, C12, and C23, slightly deviate outside the range of previous Brillouin scattering results. The present results, except those for C12, are consistent with recent lattice dynamic analysis of inelastic X-ray scattering data. The adiabatic bulk modulus was calculated as 298 GPa, which is smaller and more consistent with the result of compression experiments than any other Brillouin scattering results (301–312 GPa). The present result shows greater P-wave velocity anisotropy (24.7%) than any preceding work. To understand the unique elastic properties of stishovite, the Gingham check model was proposed and examined. The result shows that the octahedron of 6-coordinated Si in stishovite crystal has stiffness comparable to that of diamond.  相似文献   

17.
The paleomagnetic data sets from the British Tertiary Igneous Province (BTIP) have recently been criticized as being unreliable and discordant with data from elsewhere in the North Atlantic Igneous Province (NAIP) [Riisager et al. Earth Planet. Sci. Lett. 201 (2002) 261–276; Riisager et al. Earth Planet. Sci. Lett. 214 (2003) 409–425]. We offer new paleomagnetic data for the extensive lava flow sequence on the Isle of Mull, Scotland, and can confirm the paleomagnetic pole positions emanating from important earlier studies. Our new north paleomagnetic pole position for Eurasia at 59 ± 0.2 Ma has latitude 73.3°N, longitude 166.2°E (dp/dm = 5.2/7.0).A re-evaluation and an inter-comparison of the paleomagnetic database emanating from the NAIP were carried out to test for sub-province consistency. We find a general agreement between the Eurasian part of NAIP (BTIP and Faeroes) and East Greenland data. However a compilation of West Greenland data displays a large and unexplained dispersion. We speculate on if this is related to different sense of block rotation of the Tertiary West Greenland constituents. Combining all data from the NAIP constituents, give a pole position at 75.0°N, 169.9°E (N = 25, K = 84.3, A95 = 3.2) in Eurasian reference frame.  相似文献   

18.
A dacitic magma (64.5 wt.% SiO2), a mixture of phenocryst-rich rhyodacite and an aphyric mafic magma, was erupted during the recent 1991–1995 Mount Unzen eruptive cycle. The experimental and analytical results of this study reveal additional details about conditions in the premixing and postmixing magmas, and the nature of the mixing process. The preeruption rhyodacitic magma was at a temperature of 790±20°C according to Fe–Ti oxide phenocryst cores, and at a depth of 6 to 7 km (160 MPa) according to Al-in-hornblende geobarometry. The mafic magma that mixed with the rhyodacite is found as andesitic (54 to 62 wt.% SiO2) enclaves in the erupted magma and was essentially aphyric when intruded. Phase equilibria indicate that an aphyric andesite at 160 MPa is >1030°C (H2O-saturated) and possibly as high as 1130°C (2 wt.% H2O). The composition of the rhyodacite which was mixed with the andesite is estimated to lie between 67 and 69 wt.% SiO2. Using these compositions and temperatures, the temperature of the Unzen magma after mixing is estimated to be at least 850° to 870°C. The groundmass Fe–Ti oxide microphenocrysts and those in pargasite-bearing reaction zones around biotite phenocrysts both give 890±20°C temperatures; the oxide–oxide contacts give temperatures of 910±20°C. The 900±30°C postmixing temperatures are consistent with phase-equilibria experiments which show that the magma was not above 930°C at 160 MPa. Our Fe–Ti oxide reequilibration experiments suggest that the mixing of the two magmas began within a few weeks of the eruption, which is a shorter time than is calculated using available diffusion data. There is also evidence that some mixing took place much closer to the time of extrusion based on the presence of unrimmed biotite phenocrysts in the magma.  相似文献   

19.
High-pressure and high temperature experiments at 20 GPa on (Mg,Fe)SiO3 have revealed stability fields of two types of aluminium-free ferromagnesian garnets; non-cubic garnet and cubic garnet (majorite). Majorite garnet is stable only within a limited compositional variation, 0.2 < Fe/(Mg + Fe)< 0.4, and in the narrow temperature interval of 200°C around 2000°C, while the stability of non-cubic garnet with more iron-deficient compositions persists up to higher temperatures. These two garnets show fractional melting into iron-deficient garnet and iron-rich liquid, and the crystallization field of cubic garnet extends over Fe/(Mg + Fe)= 0.5. The assemblage silicate spinel and stishovite is a low-temperature phase, which also occurs in the iron-rich portion of the MgSiO3—FeSiO3 system. The sequence as given by the Fe/(Mg + Fe) value for the coexisting phases with the two garnets at 2000°C and 20 GPa is: silicate modified spinel aluminium-free garnets silicate spinel.Natural majorite in shock-metamorphosed chondrites is clarified to be produced at pressures above 20 GPa and temperatures around 2000°C. Similar shock events may cause the occurrence of non-cubic garnet in iron-deficient meteorites. Non-cubic garnet could be a stable phase in the Earth's mantle if a sufficiently low concentration of aluminium is present in the layer corresponding to the stable pressure range of non-cubic garnet. The chemical differentiation by melting in the deep mantle is also discussed on the basis of the present experimental results and the observed coexistence of majorite garnet with magnesiowüstite in chondrites.  相似文献   

20.
In this study, samples were taken from three contrasting freshwater sources and amended with salt in order to determine the influence of salinity and dissolved organic matter (DOM) composition on DOM recovery via ultrafiltration and solid phase extraction (SPE) with C18 disks. Salt addition caused variable recovery of DOM when using C18 SPE, and ultraviolet–visible spectroscopic characterization of the extracted material showed spectral responses that varied among sample sources. In contrast, increasing sample salinity from 0 to 30 ppt consistently caused a 15–25% reduction in the amount of high molecular weight DOM isolated by ultrafiltration for both dissolved organic carbon (DOC) and chromophoric DOM (CDOM), regardless of DOM composition. We hypothesize that a change in conformation (such as coiling or disaggregation) of DOM molecules occurs in the presence of salt, allowing them to pass through the ultrafiltration membrane and thereby decreasing the DOM retained by ultrafiltration. These results are important because they demonstrate that changes in salinity can influence DOM recovery in estuaries. Interpretation of DOM characteristics along estuarine gradients needs to account for potential artifacts introduced by sample isolation techniques.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号