地幔富硅交代与大陆岩石圈的演化   总被引：4，自引：0，他引：4  

陈立辉  周新华 《地学前缘》2001,8(3):141-146

富硅交代是弧下地幔中熔体岩石相互作用的主要表现形式 ,是造成古老克拉通陆下岩石圈地幔富硅的主要机制。在弧下地幔捕掳体中 ,橄榄岩被来自俯冲洋壳物质部分熔融生成的含水富硅熔体交代后 ,斜方辉石含量的增加使全岩富集SiO2 ,斜方辉石显示异常低的Al2 O3和Cr2 O3,微量元素上表现为强烈富集LILE ,强烈亏损Nb ,Ta和Ti。在古老克拉通地幔岩样品中 ,方辉橄榄岩具过剩的斜方辉石 ,橄榄石的Ni含量与斜方辉石的组成含量成正比 ,而和橄榄石的x(Mg) /x(Mg +Fe2 +)值没有正比关系 ,被解释为亏损的地幔橄榄岩和来自俯冲板片的富硅熔体相互作用的结果。熔体岩石相互作用最终导致了陆下岩石圈地幔富集SiO2 ,这种被含水富硅熔体改造后的地幔岩石的部分熔融可能是造成陆壳富硅富镁的主要原因。含水富硅熔体对岩石圈地幔的影响程度也可能是大陆岩石圈增生或裂解、增厚或减薄的关键因素之一。  相似文献   

硅灰石合成多孔二氧化硅 ——工艺条件与产物性质研究   总被引：4，自引：1，他引：4  

陈庆春  王廷吉  周萍华  彭人勇  CHEN Qing-chun  WANG　Ting-ji  ZHOU Ping-hua  PENG Ren-yong 《华东地质学院学报》2001,24(1):64-66

在一系列硅灰石酸处理实验基础上，研究了产物性质与反应速度、反应时间、中和最终pH值等工艺条件的关系。结果表明，工艺条件不同，物理性质也大不相同。  相似文献   

Geochemical processes controlling silica concentrations in groundwaters of the Salado River drainage basin, Argentina   总被引：1，自引：0，他引：1  

P. Miretzky  V. Conzonno  A. Fernndez Cirelli 《Journal of Geochemical Exploration》2001,73(3)

Chemical analyses of dissolved silica in the shallow groundwater of the lower part of the Salado River drainage basin indicate that silica values averaged 60 ppm. The groundwaters are oversaturated in relation to quartz, Na-plagioclase, K-feldspar, and the weathering of quartz and aluminosilicates appear to have little control on silica concentrations in solution. Groundwater is undersaturated with respect to amorphous silica present in the loessic sediments, and these sediments are specially important in the control of the groundwater composition. The sources of amorphous silica are volcanic glass shards and biogenic silica derived from plant (silicophytoliths, diatom frustules) or animal remains (sponge spicules) also present in the Pampean loess. Silicophytoliths and diatoms have also been reported in A soil horizon samples. The dissolution of amorphous silica most likely controls the high dissolved silica concentrations in groundwater.  相似文献   

Rapid formation of rock varnish and other rock coatings on slag deposits near Fontana,California     

Ronald I. Dorn  Norman Meek 《地球表面变化过程与地形》1995,20(6):547-560

Manganiferous rock varnish, silica glaze and iron skins have formed on 20- to 40-year-old slag piles near Fontana, southern California. Rapid rock-varnish formation is associated with an unidentified cocci bacterium that grows rapidly in culturing experiments, combined with the likelihood that Mn-rich solutions flow over slag surfaces. A new model is proposed for the formation of silica glaze, involving soluble Al-Si complexes and the nature of wetting films. Iron skins occur where runoff is concentrated, and where iron bacteria grow. Observations indicate: (i) substrate can be important in supplying Mn, as well as maintaining a stable surface and channelling runoff to microspots where varnish grows; (ii) ignorance of boundary layer pH/Eh conditions makes chemical-physical models of varnish formation speculative; (iii) the balance between cementation of recently nucleated varnishes and erosional shear stresses is poorly understood, but is probably an important limiting factor on varnish growth rates; and (iv) there must be at least two steps in biotic varnishing-accretion of Mn-Fe in casts, followed by cementation of clays by either in situ cast residue or Mn-Fe remobilized from casts. Varnish accretion may be limited by the rate at which both steps occur. Rapid development of readily distinguishable manganiferous rock varnishes at this post-1952 site highlights the danger of speculation on the ages of landforms based solely on the appearance of rock-varnish coatings.  相似文献   

^29Si,^27Al Magic—Angle—Spinning Nuclear Magnetic Resonance（MAS NMR） Studies of Kaolinite and Its Thermal Transformation Products     

He Hongping  Hu Cheng  Guo Jiugao  Zhang Huifen 《中国地球化学学报》1995,14(1):78-82

²⁷Al,²⁹Si MAS NMR studies of kaolinite and its thermal transformation products show that in the kaolinite-mullite reaction series there is an extensive segregation of Al₂O₃ and SiO₂ and the reaction of Al₂O₃ with SiO₂ to form mullite is the main path of mullite formation. At about 850° C, the peak intensity of A1(V) reaches its maximum and with the further rise of temperature the A1(V) signal completely disappears. At about 950°C, γ-Al₂O₃ accounts for about 71% of the material phases containing Al atoms. In the series there is no obvious presence of Al-Si spinel. The²⁷Al and²⁹Si MAS NMR spectra show that there is an obvious difference between the temperature points for Al-O₂(OH)₄ octahedral sheet collapsing and Si-O₄ tetrahedral sheet breaking down.  相似文献   

Formation of Colloidal Silica and Alumina During Experimental Granodiorite Weathering     

Jiří Faimon 《Aquatic Geochemistry》2003,9(4):305-341

The role of aluminum and silica in the formation of colloids during granodiorite weathering was studied on the basis of long-term experiments in batch reactors. Rock samples were dissolved in un-buffered solutions of initial pH 3.2, 5.4, and 9.9 at ambient conditions for 500 days. During weathering, extremely high supersaturation with respect to various secondary solids was attained in the solutions. Consequently, new solids, part of which was conserved in solutions as colloids, condensed. The mean concentrations of colloidal Si reached values of 70, 50, and 48 mol 1^–1 in the alkaline, neutral, and acid solutions, respectively. The mean concentrations of colloidal Al, reached values of 34, 22, and 12 mol 1^–1 in the alkaline, neutral, and acid solutions, respectively. The concentration of colloids gradually decreased after 200-400 days of experiment. This phenomenon was interpreted as being due to the competition between homogeneous nucleation and crystal growth. At the initial stages of the experiments, the colloidal species (predominantly colloidal Al) comprised a large proportion of the total amounts of aqueous species. Their share, however, decreased with time. The molar Al/Si-ratios of colloids were as high as 2–2.5 at the early stages of the experiment. After 250–300 days of experiments, on the other hand, these ratios decreased to values of about 0.5 in both the neutral and alkaline solutions and to a value of 0.15 in the acid solution. The evolution of colloids was consistent with the evolution of secondary solids in the sequence Al-hydroxides – clay minerals (illite, chlorite), in both the neutral and alkaline solutions. In acid solutions, the evolution of Al/Si-colloids was influenced by the presence of sulfate ion and Al-sulfate precipitation. Besides Al and Si, other elements, in particular Ca or Mg as a major component and Na, K, P, S, and Cl as minor components, readily participated in the formation of colloids.  相似文献   

微硅粉(纳米硅)水泥注浆技术在地质灾害防治中的应用          下载免费PDF全文

杜嘉鸿  陈兰云  王杰  王述红 《探矿工程》2005,32(1):35-38

介绍了微硅粉(纳米硅)浆材的基本性能，应用微硅粉浆材处理基础的不均匀沉降等地质灾害，解决了工程实际问题。  相似文献   

Availability of Bauxite Reserves     

Meyer  F. M. 《Natural Resources Research》2004,13(3):161-172

Based upon a large database, this paper analyzes the record of bauxite mine production, exploration success, and resource depletion and evaluates the availability of bauxite reserves in the near future. The record clearly shows that for the past 50 years world bauxite production rose by an annual increase of over 5% while per capita consumption rose during the same period by about 4%. Time trends of the world bauxite reserve life index (RLI); that is, known world reserves of a given year divided by world production of the same year, are episodic and seem to follow bauxite price cycles. The present-day RLI indicates adequate bauxite supply for about 180 years and is the same as it was in 1950. However, if an annual growth rate of 5% is considered, the currently known reserves will be exhausted within the next 20 years and the reserve base will be adequate for not more than 25 years. This scenario is based, of course, on the unrealistic assumption that future exploration efforts fail to discover additional reserves. Evaluation of the quality, in terms of bauxite signatures, and quantity of presently known bauxite prospects that may be mined in future suggests that there is sufficient potential for adequate bauxite supply for the next 20 to 25 years at least. Bauxite signatures cover a wide range of values that allows selection of the most favorable bauxite prospects for future mining, both in economic as well as environmental terms. Although, there is the general believe that the world abundance of bauxite resources will ensure sufficient supply to meet future demands significant additional reserves have to be discovered if exponential growth rates continue. As the question of future bauxite supply is subject to economic and geologic principles one has to take into consideration that increasing exploration maturity in many mineral provinces will make it difficult to locate additional bauxite reserves and that decreasing real commodity prices will influence the level of investment in bauxite exploration.  相似文献   

Diatom Paleolimnological Record of Holocene Climatic and Environmental Change in the Altai Mountains, Siberia     

Karlyn S. Westover  Sherilyn C. Fritz  Tatyana A. Blyakharchuk  Herbert E. Wright 《Journal of Paleolimnology》2006,35(3):519-541

The sedimentary diatom records of three shallow lakes in the Altai Mountains, southern Siberia, were examined to assess the nature and timing of Holocene environmental changes. Few paleoenvironmental records, especially reconstructions not based on pollen, have been reported from this region. The lakes differ in elevation, annual precipitation, and catchment vegetation. Diatom assemblages in all lakes were dominated for the entire period of record by small benthic species of Pseudostaurosira Williams & Round, Staurosira Ehrenberg, and Staurosirella Williams & Round. Planktonic taxa only occur in very low abundances (<5%). The most diverse diatom flora was found in Dzhangyskol, which is situated at the lowest elevation within a forested catchment. A lack of detailed information on the ecological preferences of the dominant taxa and the complexity of environmental drivers make direct interpretation of the diatom record difficult. However, other proxies suggest that dramatic shifts in dominance between Staurosira elliptica and Staurosirella pinnata in Grusha Ozero reflect millennial-scale variability in climate. Together, chironomids and diatoms provide evidence of a cooling possibly correlative to the Younger Dryas Stade and subsequent early-Holocene warming consistent with pollen evidence of afforestation, which also is likely linked to increased humidity. By ~6000 cal year BP, the transition to a cooler, more continental climate had begun. The diatom record of Akkol shows significantly less variation in diatom community composition, but biogenic silica accumulation rates, a proxy for diatom productivity, appear to reflect climatic variability driven by insolation trends over the past 8000 years. Long-term variability in Dzhangyskol is not clearly linked to climate.  相似文献   

Methodologies for amorphous silica analysis   总被引：1，自引：0，他引：1  

L. Saccone  D.J. Conley  D. Sauer   《Journal of Geochemical Exploration》2006,88(1-3):235

Different methodologies have been investigated for their ability to extract amorphous silica (ASi) from soils and plant phytoliths. Methodologies typically used in soil science, including oxalate, acetate and citric extractions, were used in addition to an alkaline digestion technique commonly used in the aquatic sciences. Initial results show that the alkaline technique extracts nearly an order of magnitude greater amount of ASi. The alkaline extraction technique was tested on soil samples with and without acid and peroxide pre-cleaning. Samples, which were not pre-cleaned, showed a poor extraction efficiency of amorphous silica and poor reproducibility, while cleaned soil samples gave better reproducibility and an increase in the amount of Si extracted.  相似文献