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191.
本文对北大别西部的湖北英山万家老屋、罗田七道河尹家店和安徽金寨丁埠乡李集3个片麻岩样品中锆石进行了BSE显微结构分析,并在此基础上对锆石进行了离子探针U-Pb年龄测定。结果表明北大别存在两种类型的片麻岩,它们的原岩分别形成于晋宁期和燕山期,其中英山万家老屋片麻岩的形成年龄为794Ma,后期地质事件对其锆石U-Pb年龄造成的影响较小;七道河尹家店片麻岩的形成年龄为730Ma,并可能受到燕山期岩浆事件的影响,得到了140Ma左右的变质年龄;丁埠乡李集片麻岩的形成年龄为140Ma。结合已有的年代学结果,北大别地体广泛存在晋宁期的岩浆事件,表明其可能为扬子板块的北缘。 相似文献
192.
193.
S. Sahijpal M. A. Ivanova L. L. Kashkarov N. N. Korotkova L. F. Migdisova M. A. Nazarov J. N. Goswami 《Journal of Earth System Science》1995,104(4):555-567
Ion microprobe studies of magnesium isotopic composition in igneous components from several chondritic meteorites have been
carried out to look for26Mg excess that may be attributed to the presence of the now-extinct radionuclide26Al(τ ∼ 1 Ma) at the time of formation of these objects. A positive evidence for the presence of26Al in the analysed objects will strengthen its case as the primary heat source for the early thermal metamorphism/melting
of meteorite parent bodies. Based on calculated temperature profiles inside chondritic objects of different sizes and initial26Al/27Al ratios, we have estimated the initial abundances of26Al needed to provide the heat necessary for the wide range of thermal processing seen in various types of meteorites. The
magnesium isotopic data obtained by us do not provide definitive evidence for the presence of26Al at the time of formation of the analysed igneous phases in different chondritic meteorites. Experimental evidence for a
planetary scale distribution of26Al in the early solar system to serve as a significant heat source for the thermal metamorphism and melting of meteorite parent
bodies (planetesimals) remains elusive. 相似文献
194.
Influence of hydrolysis on the sorption of metal cations by smectites: Importance of edge coordination reactions 总被引:1,自引:0,他引:1
A comparison was made between the adsorptive behaviors of Cd2+ and UO
2
2+
relative to two smectites that differed in their ratio of edge sites to fixed-charge sites. Adsorption varied with both pH and ionic strength, consistent with sorptive contributions of ion exchange and coordination reactions to edge hydroxyls. Both clay minerals exhibited a greater affinity for UO
2
2+
than for Cd2+, and the clay with a higher proportion of edge sites retained both ions more strongly. A computational model including fixed-charge sites and edge hydroxyls resulted in a good prediction of overall UO
2
2+
and Cd2+ uptake to both smectites. 相似文献
195.
本文回顾了国内外金伯利岩及其它地幔岩中发现的K、Ba、Ca、REE的Ti-Cr-Fe-Mg氧化物矿物的研究现状,包括沂蒙矿系列、蒙山矿系列及柱红石系列。在此基础上概括性地总结了笔者近一、二年对山东蒙阴金伯利岩中蒙山矿矿物所进行的微区矿物学方向研究取得的最新进展,包括:①揭示了K、Ba、Ca、REE等半径较大的元素在蒙山矿中的不均匀分布特点;②首次在金伯利岩中发现了蒙山矿系列矿物的Ca端元——Ca蒙山矿及K-Ba-Ca三个端元蒙山矿在同一矿物颗粒中的共存现象;③进行了高分辨透射电镜工作,拍摄了晶格条纹象,从而完善了蒙山矿的晶体结构资料;④确定了蒙山矿后期熔融交代形成的多种矿物相。这些研究成果,证实了地幔交代作用的存在和复杂性,应引起矿物岩石学界的充分重视。 相似文献
196.
研究了采用HLC-601离子色谱仪双柱系统,电导检测器分离测定矿物包裹体浸取液中SeO ̄(2-)_4与其它阴离子的方法。实验测得Se(Ⅵ)的最小检测浓度为0.05μg/mL,回收率为96%~102%,相对标准偏差为0.5%。耐离子色谱法与极谱法分析结果进行比较,结果基本相符。 相似文献
197.
Expressions for the effective cluster formation rates
are written in terms of neutral densities and recent laboratory data on reaction rate coefficients. At D-region heights these parameters show seasonal variations due to mesospheric temperature changes. Reduction in cluster formation rates for winter months would result in a decrease in the concentration of hydrated ions and hence reduced effective recombination coefficient for electrons. The results show latitude and seasonal variations which are similar to that of a normal winter anomaly in radio wave absorption. 相似文献
198.
Meltwaters were collected in Switzerland at the border of two alpine glaciers, the Tsanfleuron glacier resting on limestones and the Tsijiore Nouve glacier flowing over gneissic rocks. Waters were analysed by atomic absorption spectrophotometry for the four major cations. Cation exchange appears to be an essential mechanism in the explanation of the dissolved cationic content of meltwaters in the frontal zone of glaciers. This is indicated by a study of the rate and characteristics of water enrichment. The rate-determining step in the process seems to be film diffusion. The influence of this diffusion is put forward in an analysis of the rates of change in concentration of the four major cations with discharge. Glacier grinding is considered as a factor favouring cation exchange in a proglacial environment. 相似文献
199.
To understand the fundamental chemical processes of fluid–rock interaction during the pulverization of quartz grains in fault zones, quartz grains were crushed within pure water. The crushing experiments were performed batch style using a shaking apparatus. The crushing process induced a decrease in pH and an increase in hydrogen gas with increased shaking duration. The amount of hydrogen ions generated was five times larger than that of the hydrogen gas, which was consistent with the amount of Si radicals estimated from electron spin resonance measurements by Hochstrasser and Antonini (1972). This indicates that hydrogen gas was generated by consuming most of the Si radicals. The generation of hydrogen ions was most likely related to the presence of silanols on the newly formed mineral surface, implying a change of proton activities in the fluid after pulverization of quartz. 相似文献
200.
北京市大气细粒子的质量浓度特征研究 总被引:24,自引:2,他引:24
大气能见度的降低是当今国际上比较突出的城市环境问题。北京近年的监测结果表明 ,大气中通过消光作用使大气能见度下降的气溶胶细粒子的污染程度呈现上升趋势。从 2 0 0 1年对北京市气溶胶细粒子 (空气动力学直径小于 2 .5μm的粒子 ) 4个季节的采样监测结果分析 (有效采样天数为 50d)得出 ,北京市细粒子质量浓度年平均值已超过美国国家标准的 7倍以上。研究发现细粒子的质量浓度不仅与环境条件有关 ,而且与气象条件也有着密切的关系。文中以细粒子的观测数据为基础 ,结合当时的气象条件进行细粒子浓度与气象条件定量关系的研究 相似文献