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341.
江西定南车步钛铁矿田地质特征 总被引:3,自引:0,他引:3
钛是国家重要战略物资。定南车步钛铁矿田,已查明中型矿床1处,发现矿点多处,远景较好,是江西省重要钛矿田。矿田位于两个细板块的接合部,矿床主要赋存于含矿中基性岩风化壳中。 相似文献
342.
川西北中生代特提斯沉积物地球化学特征对陆源风化条件的指示意义 总被引:1,自引:0,他引:1
顾雪祥 《矿物岩石地球化学通报》1996,(1)
川西北中生代特提斯沉积物地球化学特征对陆源风化条件的指示意义顾雪祥(成都理工学院.成都610059)关键词特提斯浊积岩,风化条件,元素分配型式,碱金属-碱土金属,化学变异指数地史时期的物源区现今许多已被剥蚀破坏,因而有关这类物源区的母岩性质、同化条件... 相似文献
343.
Gregory A. Pope 《The Professional geographer》1995,47(4):375-387
Quartz is regarded as one of the minerals most resistant to chemical weathering. Nevertheless, quartz does weather under certain conditions. Several geographic phenomena, including downstream sorting of fluvial sediments, the distribution of loess, and the absence of silica in tropical soils, may be directly or indirectly related to quartz weathering. Weathering may impact the use of quartz in geographic applications of geochronology and paleoenvironmental analysis. This paper defines the molecular-scale mechanisms of chemical weathering in quartz, and presents the first examination of quartz weathering in the terrestrial environment using high resolution transmission electron microscopy (HRTEM). HRTEM images illustrate crystalline disintegration, or amorphization, of exterior surfaces and internal fractures of quartz sand grains collected from tills of the Eastern Sierra Nevada, California. Of several alternative mechanisms, in situ hydration of the crystalline matrix is the most plausible for quartz amorphization. Scale and mineral structure appear to be prominent factors in quartz amorphization; microenvironment and weathering rates may also be significant, but data are insufficient to make more precise generalizations. 相似文献
344.
D. N. Mottershead 《地球表面变化过程与地形》1989,14(5):383-398
Rapid surface lowering of bedrock is taking place in the supratidal zone by salt spray weathering. A seven-year run of data demonstrates a mean rate of lowering of 0·625 mm a?1. Considerable variation exists in annual point lowering values within measurement sites, although between-site variation is not significant. Aggregate year to year variations in surface lowering are not significant. Spatial variation in individual point values may be compensated by temporal variation over an 11-year period. There is a marked summer maximum in surface lowering rate, and this is strongly correlated with monthly air temperature. Spatially and temporally episodic swelling of the rock surface is demonstrated. This does not correlate statistically with any available climatic variable and is deemed to be a real and largely stochastic phenomenon. It is interpreted as rock bursting at the granular scale due to haloclasty. The processes most likely to be responsible for the observed rapid denudation are crystallization and thermal expansion of halite, both of which are enhanced by high summer temperatures. 相似文献
345.
Zheng Lai Ni Su Zhouyang Wu Ergang Lian Chengfan Yang Fangliang Li Shouye Yang 《地球科学进展》1986,35(7):691-703
The new non-traditional stable strontium (Sr) isotope has aroused great attention from academic scholars in terms of the continental weathering and marine Sr cycle. The analytical precision of stable Sr isotope using mass spectrometry is better than 0.03‰. The compiled δ88/ 86Sr values vary from -3.65‰ to 1.68‰ in natural reservoirs. Recent findings indicate that multiple processes can cause stable Sr isotope fractionation in Earth surface, including the incongruent dissolution of primary minerals, the formation and adsorption of secondary minerals, the precipitation of calcium carbonate, and the biological cycling. These processes lead to higher δ88/ 86Sr in the liquid phase and lower δ88/ 86Sr in the solid phase, and thus result in different geochemical behavior of stable Sr isotopes in water and sediment during the weathering processes. The δ88/ 86Sr values of river sediment decrease with the increase of weathering intensity, which has the potential to indicate chemical weathering intensity. Meanwhile, further study on the fractionation mechanisms and constraints of stable Sr isotopes in river water plays an important role in tracing chemical weathering processes within the watershed, which will lead to a better understanding of the global ocean Sr cycle. 相似文献
346.
347.
董兆祥 《吉林大学学报(地球科学版)》1987,(1)
针对风化岩体仍无理想的定量分带方法这一研究现状与工程建筑需要的矛盾,提出了对能够检测工程环境岩体风化程度的各种物理力学、矿物学和声学指标进行方差分析和特殊的“动态方差分析”方法,可对岩体风化带的划分进行定量评价,达到某一试验结果下的最佳分带效果。还结合应用实例讨论了不同地质条件下分带计算过程的相应变化和应用效果。最后指出,工程岩体分类亦可借鉴本文的研究方法。 相似文献
348.
Rock samples belonging to ten lithological types under different stages of weathering, were collected from different stratigraphical
horizons at Bhagalpur. Their densities and porosities were determined experimentally and the data obtained were fitted empirically
in a linear equation for each lithological type. The slopes of the curves, which were negative in each case, showed that the
increase in porosity for the same decrease in density were in the order, white sandstone > ferruginous sandstone > white claystone
> porphyritic gneiss > quartzite > pegmatite > amphibolite ≅ biotite gnejss > basalt ≅ dolerite. A new weathering potential
index based on the density-porosity data was proposed and the values for a specific stage of weathering for all the lithological
types studied fall within the same range. 相似文献
349.
350.
Samira Krimissa Jean-Luc Michelot Lhoussaine Bouchaou Jacques Mudry Youssef Hsissou 《Comptes Rendus Geoscience》2004,336(15):1363-1369
The origin of chloride ions in groundwater from the Chtouka-Massa plain (Morocco) was studied by using chemical and isotopic analyses of water, and petrographic and chemical analyses of rocks. It appears that the schist formation, which forms the basement of the studied aquifer, is the main source of the high Cl? concentrations in groundwater. In these schists, chloride is, for a part, probably contained in biotites, and is released into groundwater through the weathering of these minerals. However, the exceptionally high chloride contents of these schists are difficult to explain if one does not assume that they also contain evaporitic-type minerals. To cite this article: S. Krimissa et al., C. R. Geoscience 336 (2004). 相似文献