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Ti site occupancy in zircon 总被引：1，自引：0，他引：1
N.D. Tailby A.M. Walker J. Hermann J.A. Mavrogenes I.S. Rodina D. Rubatto 《Geochimica et cosmochimica acta》2011,75(3):905-921
Ti site occupancy in zircon (ZrSiO4) is fundamental to thermobarometry because substitution mechanisms control Ti content-temperature relations. Here we describe the results of three independent methods used to demonstrate that Ti substitutes for Si and not Zr in zircon. Zircon grains were synthesized from oxide powders held in a Na2WO4 flux at 1 bar and 1300 °C. Zircon grains equilibrated with rutile + cristobalite show Ti contents (1201 ppm) nearly half that of zircon grains equilibrated with srilankite ((Ti,Zr)O2) + tetragonal zirconia (2640 ppm). The lower Ti content of zircon grains produced at silica-saturated conditions indicates that Ti substitution predominately occurs on the Si site. Moreover, the higher Ti contents of silica-saturated experiments at 1 bar (1201 ppm), relative to those at 1 GPa (457 ppm, Ferry and Watson, 2007), indicates a substantial pressure effect on Ti solubility in zircon. Measured Ti K-α edge X-ray Absorption Near Edge Structure (XANES) spectra of synthetic zircon grains show energies and normalized intensities akin to those seen among tetrahedrally coordinated Ti-bearing standard minerals, strongly suggesting that Ti occupies the Si site. Density functional theory (DFT) calculations confirm that Ti substitution is most likely to occur on the Si site and predict a Ti-O bond length of 1.797 Å (compared to an average of 2.160 Å for substitution on the Zr site), in excellent agreement with X-ray Absorption Fine Structure (EXAFS) spectra of experimentally grown zircon grains which indicate a value of 1.76(1) Å. The software FEFF 8.4 was used to simulate XANES spectra from the defect structures determined by DFT for Ti substituting on both the Si and Zr sites. The predicted spectrum for Ti on the Si site reproduces all the key features of the experimental zircon spectra, whereas Ti on the Zr site is markedly different. All applied methods confirm that Ti substitutes for Si in zircon. Consequently, the Ti content of zircon at a given pressure is not only a function of temperature, but will increase with decreasing silica activity. Because elements that activate or quench cathodoluminescence (CL) in zircon are incorporated into the Zr site, a decoupling of CL from Ti contents - incorporated on the Si site in zircon is expected. This hypothesis has been verified by a systematic CL-trace element study of natural and experimental zircon. 相似文献
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The Dry Creek archeologic site contains a stratified record of late Pleistocene human occupation in central Alaska. Four archeologic components occur within a sequence of multiple loess and sand layers which together form a 2-m cap above weathered glacial outwash. The two oldest components appear to be of late Pleistocene age and occur with the bones of extinct game animals. Geologic mapping, stratigraphic correlations, radiocarbon dating, and sediment analyses indicate that the basal loess units formed part of a widespread blanket that was associated with an arctic steppe environment and with stream aggradation during waning phases of the last major glaciation of the Alaska Range. These basal loess beds contain artifacts for which radiocarbon dates and typologic correlations suggest a time range of perhaps 12,000–9000 yr ago. A long subsequent episode of cultural sterility was associated with waning loess deposition and development of a cryoturbated tundra soil above shallow permafrost. Sand deposition from local source areas predominated during the middle and late Holocene, and buried Subarctic Brown Soils indicate that a forest fringe developed on bluff-edge sand sheets along Dry Creek. The youngest archeologic component, which is associated with the deepest forest soil, indicates intermittent human occupation of the site between about 4700 and 3400 14C yr BP. 相似文献
4.
Geoenvironmental site investigation using different techniques in a municipal solid waste disposal site in Brazil 总被引：3，自引：0，他引：3
Giulliana Mondelli Heraldo Luiz Giacheti Maria Eugênia Gimenez Boscov Vagner Roberto Elis Jorge Hamada 《Environmental Geology》2007,52(5):871-887
Different geoenvironmental site investigation techniques to assess contamination from a municipal solid waste disposal site
in Brazil are presented here. Superficial geophysical investigation (geoelectrical survey), resistivity piezocone penetration
tests (RCPTU), soil samples collected with direct-push samplers and water samples collected from monitoring wells were applied
in this study. The application of the geoelectrical method was indispensable to identify the presence and flow direction of
contamination plumes (leachate) as well as to indicate the most suitable locations for RCPTU tests and soil and water sampling.
Chemical analyses of groundwater samples contributed to a better understanding of the flow of the contaminated plume. The
piezocone presented some limitations for tropical soils, since the groundwater level is sometimes deeper than the layer which
is impenetrable to the cone, and the soil genesis and unsaturated conditions affect soil behavior. The combined interpretation
of geoelectrical measurements and soil and water samplings underpinned the interpretation of RCPTU tests. The interpretation
of all the test results indicates that the contamination plume has already overreached the landfill’s west-northwest borders.
Geoenvironmental laboratory test results suggest that contamination from the solid waste disposal site has been developing
gradually, indicating the need for continuous monitoring of the groundwater. 相似文献
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采用Monte Carlo模拟手段,提出描述场地土层特性变异性对传递函数变异性影响的分析方法。选取日本Kik-Net强震数据库中软（FKSH14）、硬（FKSH12）两类场地,建立场地概率模型。应用Monte Carlo技术随机生成50组场地剖面,分别计算场地的传递函数STF及STF标准差,讨论场地土层厚度、剪切波速,以及二者组合情况下场地传递函数的标准差及场地特征频率的变化。结果显示：对于硬土场地而言,场地特征频率标准差相对于软土场地较大,且剪切波速变异性影响比土层厚度变异性的影响略大,而二者组合工况下最大;而软土场地,土层厚度、剪切波速变化工况下场地特征频率的标准差相当,比二者组合工况下略低;软、硬两类场地,土层厚度与剪切波速二者组合工况下STF的标准差比单一量变化情况下略大,但3种工况下场地STF标准差相差不明显;场地STF的标准差在场地自振频率附近的频率段取值较大,极值点与场地STF的极值点相对应。 相似文献
6.
Propagation of seismic waves through soil layers would drastically change the frequency content and amplitude-based features of ground motions at the surface. These alterations are known as seismic site effects. Computation of site effects of high-populated areas such as large cities is of great importance (e.g., it is used in development of seismic microzonation of a region). Shiraz is one of the most populous cities of Iran and is located in a high seismic hazardous region. A representative clay site in this city is selected to assess local site effects. The time series and random vibration theory procedure in the frequency domain are implemented to analyze the aforementioned site. Furthermore, the nonlinear dynamic soil behavior is simulated by the equivalent linear method and the nonlinear method via DEEPSOIL program. Three types of soil column uncertainties such as shear wave velocity, modulus reduction, and damping ratio of soil layers as well as depth of underlying rock half-space (D bed) are considered herein. The mean amplification and standard deviation of natural logarithm of amplification factors are computed for a variety of analysis types. The results of the current study show that the computed mean and standard deviation of amplification factor in ln units by considering only V S uncertainty are in good agreement with the corresponding ones by considering V S and modulus reduction and damping ratio variabilities simultaneously for the studied site. Furthermore, it seems that the effect of bedrock depth in definition of spectral shapes of the Iranian seismic building code should be taken into account. 相似文献
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基于性能的抗震设计,要求工程师设计出具有预期抗震性能的结构,一个关键因素是地震作用的确定,这在很大程度上取决于局部场地条件。通过收集和分析北京、苏州和唐山城区956个钻孔资料,建立地表20 m和30 m深土层走时平均剪切波速VS20和VS30的关系式;现场钻探获取北京城区深105 m的典型钻孔原状土样,试验给出各类土体动剪切模量和阻尼比曲线;建立北京城区170个钻孔的场地反应计算模型,采用Nakamura提出的HVSR法和陈国兴等提出的弱震法估算场地基本周期TS值,结合国内外现行抗震规范的场地分类及一些学者对场地分类的研究成果,提出两种新的场地分类建议方案：基于等效剪切波速VSE和覆盖土层厚度H（地表至剪切波速VS ≥ 500 m/s的基岩深度）的双指标场地分类方案及基于VSE、H和TS的三指标场地分类方案。提出的场地分类方案对我国现行抗震规范场地分类方法的改进有参考价值。 相似文献
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Brian N. Andrews 《Geoarchaeology》2006,21(5):461-478
Consolidation is the reduction in sediment volume that occurs in response to natural overburden loading. As void space is reduced, solid particles within the consolidating sediment undergo rearrangement, including downward displacement and reduction in inclination angle. Buried artifacts are also subject to this rearrangement. An experiment was designed to simulate consolidation of artifact‐bearing sediments and document the extent of artifact rearrangement caused by varying degrees of consolidation. Results indicate that artifacts will generally follow the downward movement of the sediment regardless of individual artifact attributes, and that significant reductions in artifact inclination angle can occur. © 2006 Wiley Periodicals, Inc. 相似文献
9.
R. L. Watkins 《GeoJournal》1997,43(3):229-239
An analysis of the physical characteristics of an established wine region in eastern California, USA was undertaken to discern if a unique combination of environmental parameters in Zinfandel vineyards could be quantitatively identified. Development of a geographic information system (GIS) method to assess land suitability for current and potential viticultural regions in a Mediterranean-type climate is the primary focus. The assessment is based on spatial frequency distributions of measurable environmental criteria derived from characteristics of existing vineyards. In fact, statistically significant differences were found at the 95% confidence interval for 6 variables, and at the 85% confidence interval for an additional 3 variables. Thus 9 of the 15 variables analyzed (53%) were discriminated statistically between the vineyard and non-vineyard areas. The findings of this study illustrate the potential of GIS techniques for viticultural land suitability analysis, while supporting and contributing to the literature on the significance of soil and topographic characteristics in viticulture. 相似文献
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A stochastic model, nonlinear site response computations, and Monte Carlo statistics are incorporated into a process which is used to synthesize the uniform-hazard site specific response spectrum. This procedure, termed the SvE procedure, uses the Monte Carlo process for simulating the seismicity in the seismic areas neighboring the investigated site and to quantify the source parameters of the earthquakes in the simulated catalogues.Stochastic simulations are then applied to each of the listed earthquakes to generate the synthetic S-wave ground accelerations. For sites which are composed of thick layers of soil, each of the synthesized accelerograms is corrected for the nonlinear response of the site. The synthetic free surface S-wave accelerations are used to compute the response spectra for a given damping.Simple statistical analysis of the obtained spectral amplitudes is applied to determine the response spectrum where each of its determined spectral amplitudes has the same prescribed probability of being exceeded.The SvE procedure is demonstrated by determining the uniform-hazard response spectrum of an arbitrarily chosen site in Israel to which hypothetical, yet realistic, soil properties have been assigned. 相似文献
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Geologic site conditions and site coefficients for estimating earthquake ground motions in the inland areas of Korea 总被引：3，自引：0，他引：3
Site characterization and site-specific ground response analyses were conducted at two representative inland areas in Korea. In situ tests included 25 boring investigations, 7 crosshole tests, 18 downhole tests and 41 SASW tests, and in the laboratory, resonant column tests were performed. The soil deposits in Korea, which were shallower and stiffer than those in the western US, were examined. The fundamental site periods were distributed in the narrow band ranging from 0.1 to 0.4 s. Most sites were designated as site classes C and D based on the mean shear wave velocity of the upper 30 m from the current Korean seismic design guide. Based on the ratio of the acceleration response spectra of ground surface to rock-outcrop, short-period (0.1–0.5 s) site coefficient, Fa ranged from 1.0 to 2.7, and mid-period (0.4–2.0 s) site coefficient, Fv ranged from 1.0 to 1.6, regardless of the input rock outcrop acceleration levels of 0.05 and 0.14 g. The site coefficients specified in the Korean seismic design guide, which is similar to NEHRP provisions and UBC, underestimate the ground motion in the short-period band and overestimate the ground motion in the mid-period band. These differences can be explained by the differences in the depth to bedrock and the soil stiffness profile between Korea and western US. Also, the site coefficients should be re-evaluated accounting for the local geologic conditions on the Korean peninsula. 相似文献
12.
《Engineering Geology》2006,82(4):446-469
Site characterization and site-specific ground response analyses were conducted at two representative inland areas in Korea. In situ tests included 25 boring investigations, 7 crosshole tests, 18 downhole tests and 41 SASW tests, and in the laboratory, resonant column tests were performed. The soil deposits in Korea, which were shallower and stiffer than those in the western US, were examined. The fundamental site periods were distributed in the narrow band ranging from 0.1 to 0.4 s. Most sites were designated as site classes C and D based on the mean shear wave velocity of the upper 30 m from the current Korean seismic design guide. Based on the ratio of the acceleration response spectra of ground surface to rock-outcrop, short-period (0.1–0.5 s) site coefficient, Fa ranged from 1.0 to 2.7, and mid-period (0.4–2.0 s) site coefficient, Fv ranged from 1.0 to 1.6, regardless of the input rock outcrop acceleration levels of 0.05 and 0.14 g. The site coefficients specified in the Korean seismic design guide, which is similar to NEHRP provisions and UBC, underestimate the ground motion in the short-period band and overestimate the ground motion in the mid-period band. These differences can be explained by the differences in the depth to bedrock and the soil stiffness profile between Korea and western US. Also, the site coefficients should be re-evaluated accounting for the local geologic conditions on the Korean peninsula. 相似文献
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This paper highlights the seismic microzonation carried out for a nuclear power plant site. Nuclear power plants are considered to be one of the most important and critical structures designed to withstand all natural disasters. Seismic microzonation is a process of demarcating a region into individual areas having different levels of various seismic hazards. This will help in identifying regions having high seismic hazard which is vital for engineering design and land-use planning. The main objective of this paper is to carry out the seismic microzonation of a nuclear power plant site situated in the east coast of South India, based on the spatial distribution of the hazard index value. The hazard index represents the consolidated effect of all major earthquake hazards and hazard influencing parameters. The present work will provide new directions for assessing the seismic hazards of new power plant sites in the country. Major seismic hazards considered for the evaluation of the hazard index are (1) intensity of ground shaking at bedrock, (2) site amplification, (3) liquefaction potential and (4) the predominant frequency of the earthquake motion at the surface. The intensity of ground shaking in terms of peak horizontal acceleration (PHA) was estimated for the study area using both deterministic and probabilistic approaches with logic tree methodology. The site characterization of the study area has been carried out using the multichannel analysis of surface waves test and available borehole data. One-dimensional ground response analysis was carried out at major locations within the study area for evaluating PHA and spectral accelerations at the ground surface. Based on the standard penetration test data, deterministic as well as probabilistic liquefaction hazard analysis has been carried out for the entire study area. Finally, all the major earthquake hazards estimated above, and other significant parameters representing local geology were integrated using the analytic hierarchy process and hazard index map for the study area was prepared. Maps showing the spatial variation of seismic hazards (intensity of ground shaking, liquefaction potential and predominant frequency) and hazard index are presented in this work. 相似文献
15.
Young-Ji Han Pyung-Rae Kim Gang-San Lee Jae-In Lee Seam Noh Seok-Min Yu Kwang-Su Park Kwang-Seol Seok Hyuk Kim Young-Hee Kim 《Environmental Earth Sciences》2017,76(10):361
Mercury (Hg) concentrations in air, effluent water, landfill gas, leachate, groundwater, and soil at a hazardous solid waste landfill site in Korea were measured along with air–soil surface Hg exchange fluxes at the site. The concentrations and fluxes were considerably higher than have been found elsewhere in Korea. Gaseous Hg concentrations in the air peaked during the day, coinciding with Hg being released from the landfill surface. This suggests that air–soil exchange increased the Hg concentrations in the atmosphere. The air–soil exchange flux increased abruptly when solar radiation reached the soil surface. The Hg flux peaked about 3 h before the solar radiation peaked, possibly because reducible Hg was abundant at the soil surface. The Hg emission flux activation energy (E a) was low, indicating that the Hg species present and Hg–soil binding were probably not as important (because of the high Hg content of the soil) as in previous studies. The methylmercury to total Hg ratios in the discharged effluent, groundwater, and leachate was clearly higher than typically found in coastal water and freshwater, suggesting bacteria caused active methylation to occur under the reducing conditions in the anaerobic landfill. The results suggested that considerable amounts of Hg are probably transported from the landfill to nearby environmental media and that this will continue if waste with a high Hg content continues to be added to the landfill without being pretreated. 相似文献
16.
本文采用工程抗震理论,结合场地实际状况,论述了某电力扩建场地的区域构造条件和区域地震环境,确定了场地的地震动参数,并采用概率地震危险性分析法对扩建场地进行地震危险性分析,从而为该工程建设提供合理的设计依据. 相似文献
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Jean H. Prevost 《国际地质力学数值与分析法杂志》1986,10(6):653-665
A procedure is presented which allows site response analyses to be performed with any general multidimensional finite element analysis package. Numerical results which corrorate the theory are presented. Also, as an illustration of the procedure, results of an effective stress analysis for the scismic response and liquefaction of a horizontally layered saturated sand deposit are presented. 相似文献
18.
Maximilian Huber Fabrizio Marconi Massimiliano Moscatelli 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2015,9(1):49-56
The evaluation of the underground soil stratigraphy is a key aspect in geotechnical site characterisation. However, these means of site exploration are only pinholing subsoil conditions and expert knowledge is needed to understand subsoil conditions in order to build a reliable geological-geotechnical model. This contribution employs a geostatistical simulation methodology for the simulation of random fields representing geological uncertainty. This combines borehole data and expert knowledge via a mathematical framework. Moreover a risk-based site characterisation scheme is developed for urban site characterisation. This novel characterisation scheme offers additional insight into the effects of large-scale, geological spatial variability by using fragility curves to quantify these effects. 相似文献
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It is well known that in pyroxene structure,there are two metal sites,M1 and M2.Generally speaking,Ferrous iron in each of these sites would normally be expected to give rise to a doublet,However,anomalies have been found in the relative areas of the peaks in the room temperature spectra of some clinopyroxene(CPX)when the above assignment is followed.According to the calculation of Next Nearest Neighbor configurations of divalent cations in M1,we found that the four configurations of M1 can be divided into two groups.One group is 3Ca configuration that increases with the content of Ca(p.f.u);the other group is made up of three No-3Ca configurations that decrease with the content of Ca.The two groups contribute to the spectrum structure of M1.so in this study we fit two doublets for ferrous iron in M1.Though there were several reports on Fe^3 in tetrahedral site previously,it was not sure that Fe^3 occupies the T site is a universal fact in CPX,despite of the content of Al.We found that the Fe^3 in the T site fitted by Moessbauer spectroscopy is negatively correlated to the Si content in the T site and positively correlated to the Fe^3 in the T site estimated on the supposition that Fe^3 and Al occupy the T site randomly.If it is true.it is important in the modeling of ion exchange geobarometries and geothermomeries. 相似文献
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史期时期，人类社会的生产力还十分低下，自然环境对古人类体质的进化、生产的发展，以及居住范围的变化都产生了重大的影响。通过孢粉分析和对其他植物遗存的研究复原古植被特征，同时结合广汉层古土壤地球化学行为、古河流的水动力等，来综合研究金沙遗址区古环境状况，以期能为古蜀文化研究提供环境背景。研究结果表明，文化期内总体上是热带和亚热带的温暖湿润气候，同时存在着温暖湿润与温暖干旱的气候交替。 相似文献