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151.
Fifteen samples of (Mg,Fe)SiO3 majorite with varying Fe/Mg composition and one sample of (Mg,Fe)(Si,Al)O3 majorite were synthesized at high pressure and temperature under different conditions of oxygen fugacity using a multianvil press, and examined ex situ using X-ray diffraction and Mössbauer and optical absorption spectroscopy. The relative concentration of Fe3+ increases both with total iron content and increasing oxygen fugacity, but not with Al concentration. Optical absorption spectra indicate the presence of Fe2+–Fe3+ charge transfer, where band intensity increases with increasing Fe3+ concentration. Mössbauer data were used in conjunction with electron microprobe analyses to determine the site distribution of all cations. Both Al and Fe3+ substitute on the octahedral site, and charge balance occurs through the removal of Si. The degree of Mg/Si ordering on the octahedral sites in (Mg,Fe)SiO3 majorite, which affects both the c/a ratio and the unit cell volume, is influenced by the thermal history of the sample. The Fe3+ concentration of (Mg,Fe)(Si,Al)O3 majorite in the mantle will reflect prevailing redox conditions, which are believed to be relatively reducing in the transition zone. Exchange of material across the transition boundary to (Mg,Fe) (Si,Al)O3 perovskite would then require a mechanism to oxidize sufficient iron to satisfy crystal-chemical requirements of the lower-mantle perovskite phase. 相似文献
152.
D. M. Bonotto 《Environmental Geology》2005,48(4-5):507-523
U-modeled groundwater residence times were estimated by changes in 234U/238U activity ratio (AR) and U content of groundwaters from Poços de Caldas city situated at the Poços de Caldas alkaline massif, Brazil. The estimated ages are more realistic than others generated by the use of hydraulic conductivity data and available information about the weathering rate of rocks in the plateau. The 234U/238U AR and reciprocal of the dissolved U-content data also defined a ternary plot that allowed the calculation of the relative volume of three source waters for the mixed water. Such U-isotopes modeling for mixing calculations indicated that the dominant phase (68%) in the mixture is thermal. 相似文献
153.
154.
在协调元基础上,通过一次逼近理论,建立随机有限元模型,并通过模糊数学模型实现对边坡体工作状态的软化处理;借助于模糊随机数值方法对荆南长江干堤局部破坏失效进行了较为全面的研究。 相似文献
155.
Interaction between the Quasi-Biennial Oscillation in far west equatorial Pacific (QBOWP) and the El Ni?o/Southern Oscillation
(ENSO) is studied using a new conceptual model. In this conceptual model, the QBOWP effects on ENSO are achieved through two
ways: (1) the oceanic Kelvin wave along equatorial Pacific, and (2) the Atmospheric Walker Circulation anomaly, while ENSO
effects on QBOWP can be accomplished by the atmospheric Walker Circulation anomaly. Diagnosis analysis of the model results
shows that the Atmospheric bridge (Walker circulation) plays a more important role in interaction between the ENSO and QBOWP
than the oceanic bridge (oceanic Kelvin wave along equatorial Pacific); It is found that by the interaction of the ENSO and
QBOWP, a free ENSO oscillation with 3–5 years period could be substituted by a oscillation with the quasi-biennial period,
and the dominant period of SST anomaly and wind anomaly in the far west equatorial Pacific tends to be prolonged with enhanced
ENSO forcing. Generally, the multi-period variability in the coupled Atmosphere-Ocean System in the Tropical Pacific can be
achieved through the interaction between ENSO and QBOWP. 相似文献
156.
157.
158.
抚仙湖-星云湖出流改道工程环境影响分析 总被引:1,自引:0,他引:1
抚仙湖、星云湖综合治理出流改道工程旨在“保护抚仙湖、改善星云湖、不影响东风水库水质”,不仅涉及到玉溪市饮用水源的保护和城市水源的长远发展规划,还涉及到东风水库、曲江和海口河至南盘江及其沿岸城市引水工程的防洪度汛,及两湖一库(抚仙湖、星云湖、东风水库)流域的生物多样性保护和自然生态环境保护。因此,工程实施前对工程的主要生态环境影响进行全面的分析非常必要。对工程所涉及到的抚仙湖、星云湖和东风水库的水质、生态效应、生物交流以及流域内的相关用水工程的影响作较为全面的分析,旨在为工程的进一步实施提供决策参考。 相似文献
159.
广东省两类不同成因类型花岗岩磁化率各向异性研究表明:Ⅰ型花岗岩的磁化率的数值较大,一致性较好;各向异性度比较小,磁化率椭球为纯压扁型.S型花岗岩的磁化率数值普遍较小,一致性较差;各向异性度比较大,磁化率椭球以兼具压扁型和拉长型为特征;岩体内部两种磁化率椭球(压扁型和拉长型)的3个主轴的方向具有较好的一致性.结合花岗岩的野外地质特征,作者认为,S型花岗岩在形成过程中受到了板块内部强烈的挤压和剪切作用,不同类型的源岩在强烈的挤压作用下局部地带发生破裂,发育了大规模的剪切推覆作用,在剪切热的作用下源岩物质被改造形成S型花岗岩;Ⅰ型花岗岩则是原始岩浆侵入到地壳上部形成,其形成的构造背景与当时板块的B型俯冲有关。 相似文献
160.
Bill Broyles 《Journal of Arid Environments》1996,33(4):483-495
Water for personal use was a limiting factor for the prehistoric and historic indigenous peoples who inhabited the extremely arid North American region of south-western Arizona and north-western Sonora, known as Papaguer?́a. This paper lists and quantifies the perennial and intermittent water resources available to them. In the 16,824 km2study area of the Sonoran Desert, there were 128 waterholes, most of them in the mountains and, when full, these offered at least 3,099,141 l of water. At today's precipitation levels, virtually all points of the region were accessible to inhabitants within a 40 km radius of one or more water sources. 相似文献