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951.
952.
A. D. Shukla N. Bhandari Sheela Kusumgar P. N. Shukla Z. G. Ghevariya K. Gopalan V. Balaram 《Journal of Earth System Science》2001,110(2):111-132
Chemical analysis of nine Deccan flow basalts at Anjar, Kutch, western India, indicates that all, except the uppermost flow
F-9, are alkaline. In their major and trace element composition, the alkali basalts resemble Ocean island basalts (OIB). Similarities
of many diagnostic trace element ratios (e.g. Sm/Nd, Ba/Nb,Y/Nb and Zr/Nb) are similar to those found in the Réunion Island
basalts. The uppermost basalt is tholeiitic and chemically resembles the least contaminated Deccan basalt (Ambenali type).
The Anjar basalts have iridium concentration ranging between 2 and 178 pg/g. Some of these values are higher by about an order
of magnitude compared to the Ir concentration in other basalts of the Deccan. A synthesis of chemical, palaeomagnetic and
geochronologic data enables us to construct a chemical and magnetic stratigraphy for these flows.
The three flows below the iridium enriched intertrappean bed (IT III) show normal magnetic polarity whereas all except one
of the upper basalts show reversed magnetic polarity. The sequence seems to have started in polarity zones 31N and probably
continued up to 28R or 27R. The results presented here support the view that Deccan volcanism in Kutch occurred on a time
span of a few million years. 相似文献
953.
Modeling of dioctahedral 2:1 phyllosilicates by means of transferable empirical potentials 总被引:1,自引:0,他引:1
C. I. Sainz-Diaz A. Hernández-Laguna M. T. Dove 《Physics and Chemistry of Minerals》2001,28(2):130-141
Dioctahedral 2:1 phyllosilicates with different interlayer charge have been studied theoretically by using transferable empirical
interatomic potentials. The crystal structures of pyrophyllite, muscovite, margarite, beidellite, montmorillonite, and different
smectites and illites have been simulated. The interatomic potentials were able to reproduce the experimental structure of
phyllosilicates with high, medium and low interlayer charge. The calculated structures are in agreement with experiment for
the main structural features of the crystal lattice. The effect of the cation substitution in the octahedral and tetrahedral
sheets on the structural features has been also studied. Good linear relationships have been found, and the calculated effects
are consistent with experimental results. Some unknown structural features of the crystal structures of clays are predicted
in this work.
Received: 8 March 2000 / Accepted: 19 September 2000 相似文献
954.
Polarized electronic single crystal spectra of natural Fe2+ ion-bearing oxygen-based minerals, in which ferrous ions enter octahedral sites of different symmetry and distortion (olivine,
cordierite, ortho- and clinopyroxene, amphibole), eightfold sites in garnet (almandine) and clinopyroxene (M2), and tetrahedral
sites in spinel, were studied at temperatures from 300 to ca. 600 K. In the minerals studied, the spin-allowed bands of Fe2+ display rather variable temperature behaviour. In most cases, due to the thermal expansion of the Fe2+-bearing polyhedra, bands shift to lower energies upon increasing temperature, though there are some exceptions to this rule:
in cases of other than sixfold octahedral or close to octahedral coordination, in almandine and spinel the bands shift to
higher energies, which can be explained by an increase in distortions of the Fe2+-bearing polyhedra. Splitting of the excited 5
E
g-level of Fe2+ ions usually, but not always, increases with temperature, reflecting thermally induced increase in distortion of the Fe2+-bearing sites in the minerals studied. Integral intensities of the bands in question do not always obey the general rule,
according to which intensity should increase with temperature, when the 3d
N-centred site is centrosymmetric, or should remain unchanged when the 3d
N site lacks an inversion centre. The experimental results show that the response of the characteristics of absorption bands
such as width, intensity and energy caused by dd transitions of Fe2+ in oxygen-based minerals to increasing temperature is not always uniform and is at variance with expectation. This temperature
dependence cannot be used directly to solve band assignment problems, as earlier proposed in the literature.
Received: 22 December 1999 / Accepted: 30 October 2000 相似文献
955.
该种方法利用离子色谱仪的电导检测器与电化学检测器串联 ,十几分钟即可连续完成水中S2 - 、SO2 - 3 、SO2 - 4、S2 O2 - 3 的测定 ,方法具有快速、高效、方便、灵敏、选择性好等特点。方法的检出限分别为 :S2 - 12 5 μg/L ;SO2 - 3 2 2 4 μg/L ;SO2 - 45 0 μg/L ;S2 O2 - 35 0 μg/L。相对标准偏差在 1 5 %~ 6 9%之间 ,能够满足水中S2 - 、SO2 - 3 、SO2 - 4、S2 O2 - 3四种阴离子分析测试的需要。 相似文献
956.
957.
Zhao Wenyu Center of Material Research Analysis Wuhan University of Technology Wuhan Liu Rong Wang QinyanFaculty of Earth Sciences China University of Geosciences Wuhan Peng Changqi Zhang QingjieCenter of Material Research Anal 《中国地质大学学报(英文版)》2001,12(3)
INTRODUCTIONItisanacknowledgedfactthataragonite,ahigh pressurepolymorphofCaCO3 ,occurswidelyasanindexmineralofhigh pressureandlow temperaturemetamorphism (glaucophaneschistfacies)withinthegeodynamiccontextofsubduction obductionandcontinentalcollision (Liou… 相似文献
958.
P. N. Shukla N. Bhandari Anirban Das A. D. Shukla J. S. Ray 《Journal of Earth System Science》2001,110(2):103-110
We report here an unusually high concentration of iridium in some alkali basalts and alkaline rocks of Deccan region having
an age of about 65Ma, similar to the age of the Cretaceous-Tertiary boundary. The alkali basalts of Anjar, in the western
periphery of Deccan province, have iridium concentration as high as 178pg/g whereas the alkaline rocks and basalts associated
with the Amba Dongar carbonatite complex have concentrations ranging between 8 and 80 pg/g. Some of these values are more
than an order of magnitude higher than the concentration in the tholeiitic basalts of Deccan, indicating the significance
of alkaline magmatism in the iridium inventory at the Cretaceous-Tertiary boundary. Despite higher concentration, their contribution
to the global inventory of iridium in the Cretaceous-Tertiary boundary clays remains small. The concentration of iridium in
fluorites from Amba Dongar was found to be <30 pg/g indicating that iridium is not incorporated during their formation in
hydrothermal activity. 相似文献
959.
本文研究时间序列的变点问题。所给出的统计方法可用来推断一个时间序列是否存在变点,存在几个变点以及变点在什么位置。这种统计推断方法可用于气候阶段的划分。 相似文献
960.
中国大陆卫星反演云参数的评估 总被引:29,自引:6,他引:29
该文选取1983年7月和1984年1月份代表夏季和冬季,利用中国地面气象月报的云量资料以及多年平均的地面观测云气修资料,与中国大陆地区ISCCP卫星反演的去量和云状资料进行了对比分析。参照大气环流和云天气气候特征,从卫星得到的从云状是比较合理的,但干旱沙漠地区的高云量的估计不足,低云估计偏多。 相似文献