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61.
The Palghat Gap region is located near the centre of the large southern Indian granulite terrane. at the northern edge of the Kodaikanal charnockite massif. The dominant rock types in the region are hornblende-biotite ± orthopyroxene gneisses and charnockites along with minor amounts of intercalated mafic granulite, metapelite and calc-silicate. The P-T estimates from garnetiferous mafic granulites and metapelite samples are generally in the range 9-10 kbar and 800-900 C using both conventional thermobarometric methods and the TWEEQU thermobarometry program. These P-T estimates, which should be taken as minimum values, are among the highest yet reported for South Indian and Sri Lankan granulites. The occurrence of orthopyroxene + plagioclase symplectites around embayed garnet grains in the mafic granulites and cordierite rims around garnet grains in metapelite suggest an isothermal decompression-type path. Similarly, a core-rim P-T trajectory indicates c. 3 and 7 kbar decompression at high temperature in the mafic granulites and metapelite, respectively. In both rock types, the key to the determination of the retrograde P-T path was the recognition of small amounts of second generation plagioclase with a more anorthitic composition than the matrix plagioclase. The preservation of high garnet-pyroxene temperatures in the mafic granulites (despite small garnet grain size) suggests rapid cooling of the terrane. Calculated minimum cooling rates range from 8 to 80 C Ma-1 . Such cooling rates are more rapid than those associated with normal isostatic processes and suggest that the terrane was tectonically exhumed at high temperature. 相似文献
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A statistically relevant correlation between the reaction rate coefficient, k
OH, for the OH radical reaction with 161 organic compounds in the gas phase at 300 K, and the corresponding vertical ionisation energies E
i,v, reveals two classes of compounds: aromatics where –log(k
OH/cm3s-1)3/2E
i,v(eV)–2 and aliphatics where –log(k
OH/cm3s-1)4/5E
i,v(eV)+3. The prediction of the rate coefficient, k
OH, for the reaction of OH with organic molecules from the above equations has a probability of about 90%. Assuming a global diurnal mean of the OH radical concentration of 5×105 cm3, the upper limit of the tropospheric half-life of organic compounds and their persistence can be estimated. 相似文献
64.
The chemistry of glycolaldehyde (hydroxyacetaldehyde) relevant to the troposphere has been investigated using UV absorption spectrometry and FTIR absorption spectrometry in an environmental chamber. Quantitative UV absorption spectra have been obtained for the first time. The UV spectrum peaks at 277 nm with a maximum cross section of (5.5± 0.7)×10–20 cm2 molecule–1. Studies of the ultraviolet photolysis of glycolaldehyde ( = 285 ± 25 nm) indicated that the overall quantum yield is > 0.5 in one bar of air, with the major products being CH2OH and HCO radicals. Rate coefficients for the reactions of Cl atoms and OH radicals with glycolaldehyde have been determined to be (7.6± 1.5)×10–11 and (1.1± 0.3)×10–11 cm3 molecule–1 s–1, respectively, in good agreement with the only previous study. The lifetime of glycolaldehyde in the atmosphere is about 1.0 day for reaction with OH, and > 2.5 days for photolysis, although both wet and dry deposition should also be considered in future modeling studies. 相似文献
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ZHANG Ronghu HU Shumin SU YanfengOpen Research Laboratory of Geochemical Kinetics Institute of Mineral Resources Chinese Academy of Geological Sciences Baiwanzhuang Ro Beijing China 《《地质学报》英文版》2002,76(3):351-366
This study reports the kinetic experimental results of albite in water and in KCI solution at 22 MPa in the temperature range of 25 to 400℃. Kinetic experiments have been carried out in an open flow-through reaction system (packed bed reactor). Albite dissolution is always incongruent in water at most temperatures, but becomes congruent at 300℃ (close to the critical point 374℃). At temperatures from 25 to 300℃, the incongruent dissolution of albite is reflected by the fact that sodium and aluminum are easily dissolved into water; from 300 to 400℃ it is reflected by silicon being more easily dissolved in water than Al and Na. Maximum albite dissolution rates in the flow hydrothermal systems have been repeatedly observed at 300℃, independent of flow rates.The kinetic experiments of albite dissolution in a KCl aqueous solution (0.1 mol KCl) indicate that the dissolution rate of albite increases with increasing temperature. Maximum silicon release rates of albite have been observed at 400℃, while ma 相似文献
67.
采用(斜长石+黑云母+石英)这三种单矿物组合与1mol/L NaCl或0.5mol/L NaCl 0.5mol/L NaHCO3溶液在450-250℃和50MPa条件下反应7d。实验表明,反应后流体pH值发生了变化,NaCl介质向酸性变化,N aCl NaHCO3介质向中性转化。溶液中K,Ca,Mg,Fe和Au量也随之发生变化。矿物表面发生溶解和离子置换等反应。斜长石表面形成钠长石反应边,黑云母变色,石英重结晶,反应器皿金管中的金被溶解后在金管壁和黑云母表面重结晶,黑云母周边出现红色Fe2O3,在450℃的NaCl介质中,金含量可达1070μg/g,但随温度下降迅速减低,在NaCl NaHCO3介质中,金含量较低,显著,金的活化迁移和富集与Cl,pH,Fe^3 /Fe^2 密切相关,这中金起到示踪作用,显示出金在水/岩反应中的原电池效应。 相似文献
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pH值对长石溶解度及次生孔隙发育的影响 总被引:19,自引:0,他引:19
本文从长石溶解反应的机理及各离子形态在溶液中分布的热力学角度出发 ,论述了pH值对三个长石端员及高岭石在流体中溶解度的影响。在此基础上 ,进一步探讨了流体酸碱度对长石向高岭石转化和次生孔隙发育程度的制约 ,并提出了衡量次生孔隙发育程度的参数———转化系数D。 相似文献
70.