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   

Period variations of the Chandler wobble   总被引：1，自引：0，他引：1  

H. Jochmann 《Journal of Geodesy》2003,77(7-8):454-458

Variations in the period of the Chandler wobble have been discussed since its discovery by Chandler in 1892. Various authors engaged in the investigation of polar motion time series suggest both a variable and an invariable period. It cannot be resolved by the analysis of time series whether the Chandler period is variable. By studying the influence of mass redistributions on the Chandler period it has been found that it is in fact variable, but the magnitude of such variation is much smaller than that found by polar motion time series analysis. For the currently available time series of polar motion, it is sufficient to assume an invariable Chandler period. AcknowledgmentsUseful discussions with Dr. F. Barthelmes and Dr. K. Fleming are gratefully appreciated.  相似文献   

1303年山西洪洞8级大地震的时间有序性特征   总被引：5，自引：0，他引：5  

徐道一 《山西地震》2003,(3):34-36

1303年山西洪洞地震是我国历史记录中被确认的第一个8级大地震。引入有序系列和有序组合的含义,对1303年山西洪洞地震和1556年陕西华县地震分别形成的2个有序系列进行了研究,认为2个8级地震的发震时间有一个时间差(τ)。2个τ值之差用△τ来表示。若2个τ值相差不大,则4个地震(有时可以是3个地震)组成一个有序组合。2个有序系列可有7个有序组合。7个有序组合的τ值在100a～450a范围变化,但它们的△τ值仅在10d～2400d范围内变化,表示了2个有序序列之间的密切联系。震例表明,1303年洪洞大地震与其他8级地震之间的间隔的形成机制可能与沙罗周期有关。  相似文献   

The distribution of inselbergs and their relationship to geomorphological, structural and lithological controls in Southern Zimbabwe     

Wolfgang Rmer 《Geomorphology》2005,72(1-4):156-176

The gneissic-granitic basement of southern Zimbabwe is characterized by a wide variety of inselbergs, preferentially developed on the granitoid rocks. However, there are significant differences in the frequency of inselbergs and most inselbergs occur in the younger granitoid rocks, particularly in rocks with microcline as the dominant K-feldspar, but their distribution is not uniform. Completely isolated inselbergs are rare and most inselbergs are arranged in clusters or are associated with plateaus or they occur as the detached ends of spurs and ridges.Chemical and mineralogical investigations indicate significant differences in the composition of the older and younger granitoid rocks. The latter are characterized by a higher content of alkali feldspars and a lower content of plagioclase and mafic minerals.The influences of texture, fabric and fracture characteristics on the resistance of the rocks vary. In the southern part of the study area the majority of rock domes is associated with porphyritic granites and fine-grained granites, whilst inselbergs of the large batholith complexes in the northern part of the study area show virtually no relationships to the grain-size of the rocks.Thin-sections analysis indicate, that the rocks of the terrains with a higher density of inselbergs are characterized by an intense intergrowth of minerals and a higher number of contacts between quartz and alkali feldspars. Particularly in the case of the porphyritic granites the influence of texture on the frequency of rock domes is linked with two factors. These are a high content of microcline minerals that have filled the interstices of the surrounding mineral framework and enclosed the surrounding minerals. Overgrowths and replacement micro-structures indicate a long lasting crystallization, which appears to be responsible for a lower density of cooling fractures. Enclosure of the more vulnerable minerals in the more resistant microcline megacrysts retards the loosening of the rock constituents.The marked differences in the lithological and structural characteristics of the various granitoid rocks influence the weathering behaviour of the rocks and illustrate that the divergent weathering characteristics of the rocks are strongly dependent on lithological and structural factors.  相似文献   

Australian Rock Coasts: review and prospects     

Wayne J. Stephenson  Lukar E. Thornton 《The Australian geographer》2005,36(1):95-115

Studies of Australian rock coasts (except carbonate reefs) are reviewed and considered in view of recent process and morphological studies. The unique nature of the Australian coast, its geographical distribution and relative stability mean that it is a productive environment in which to research fundamental questions concerning rock coasts. Future research directions are identified, specifically in the areas of processes, morphology and modelling.  相似文献   

Localized Weathering: Implications for Theoretical and Applied Studies     

Steven J. Gordon  Ronald I. Dorn 《The Professional geographer》2005,57(1):28-43

In situ quantification of localized weathering processes on basalt flows in New Mexico and Hawaii demonstrates that small‐area factors can be more important than other more readily observable factors. Further, it demonstrates that the factorial concept of the Pope Boundary‐Layer weathering model is partially solvable, that organic weathering can accentuate glass weathering (with implications for climate models and storage of nuclear waste), and that silica coatings are not a simple solution for the preservation of stone monuments. Enhancement of glass weathering by lichens on the McCartys flow, El Malpais National Monument, New Mexico, remains restricted to a half‐millimeter directly underneath the lichen‐covered surface. In contrast, although the inorganic rock coating of silica glaze reduces weathering directly underneath the coating by up to nine times rates found in uncoated locales, silica glaze can almost double variability in weathering along its margins.  相似文献   

安徽梅雨年际变化特征研究   总被引：7，自引：5，他引：7       下载免费PDF全文

刘勇  徐敏  朱红芳  郑启康 《气象科学》2004,24(4):488-494

本文对安徽省1951～2002年52a的入梅日期、出梅日期、梅雨日数、梅雨期降水总量等数据进行了统计。反映梅雨期年际变化特征的分析结果表明：安徽省入梅日期主要集中在6月的第2候和第4候，出梅日期主要集中在7月第2候；入梅日期的早晚与梅雨期天气形势、梅雨日数、梅雨期总降水量有着一定的对应关系。文中揭示的有关梅雨期年际变化特征，对于做好入梅日期、梅雨日数、梅雨期总降水量的预报，进而做好防汛抗旱的服务工作具有一定的参考意义。  相似文献   

Estimation of fundamental period for structures supported on pile foundations     

Sanjeev Kumar  Shamsher Prakash 《Geotechnical and Geological Engineering》2004,22(3):375-389

One of the significant effects of considering soil-structure interaction in the analysis of structures is the increase in the fundamental natural period compared to the fundamental natural period of a similar structure, fixed at the base. Applied Technology Council (ATC) originally set forth some provisions to calculate the fundamental natural period of flexible based structures using the period of a similar structure, fixed at the base, and lateral and rocking stiffness coefficients of the foundation. These provisions became the basis of current soil-structure interaction recommendations in several building codes. The fundamental natural periods of structures founded on different types of foundations computed using recommendations of the ATC are compared with those computed using a simplified model to perform soil-structure interaction of shear-type structures. Results show that the provisions given in ATC may be used for structures supported on shallow footings but may not be applicable for structures supported on pile foundations or foundations having the ratio of lateral to rotational stiffness coefficients different from those of shallow foundations. An equation, similar to the equation recommended by ATC, is presented to estimate the fundamental natural period of structures supported on pile foundations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

草盛期不同类型高寒草甸CO2释放速率的比较研究     

胡启武  曹广民  吴琴  LI Dong  WANG Yuesi 《地理学报(英文版)》2004,14(2):67-176

Potentilla fruticosa scrub, Kobresia humilis meadow and Kobresia tibetica meadow are widely distributed on the Qinghai-Tibet Plateau. During the grass exuberance period from 3 July to 4 September, based on close chamber-GC method, a study on CO2 emissions from different treatments was conducted in these meadows at Haibei research station, CAS. Results indicated that mean CO2 emission rates from various treatments were 672.09±152.37 mgm^-2h^-1 for FC (grass treatment); 425.41±191.99 mgm^-2h^-1 for FJ (grass exclusion treatment); 280.36±174.83 mgm^-2h^-1 for FL (grass and roots exclusion treatment); 838.95±237.02 mgm^-2h^-1 for GG (scrub+grass treatment); 528.48±205.67 mgm^-2h^-1 for GC (grass treatment); 268.97±99.72 mgm^-2h^-1 for GL (grass and roots exclusion treatment); and 659.20±94.83 mgm^-2h^-1 for LC (grass treatment), respectively (FC, FJ, FL, GG, GC, GL, LC were the Chinese abbreviation for various treatments). Furthermore, Kobresia humilis meadow, Potentilla fruticosa scrub meadow and Kobresia tibetica meadow differed greatly in average CO2 emission rate of soil-plant system, in the order of GG>FC>LC>GC. Moreover, in Kobresia hurnilis meadow,heterotrophic and autotrophic respiration accounted for 42% and 58% of the total respiration of soil-plant system respectively, whereas, in Potentilla fruticosa scrub meadow, heterotrophic and autotrophic respiration accounted for 32% and 68% of total system respiration from GG; 49% and 51% from GC. In addition, root respiration from Kobresia humilis meadow approximated 145 mgCO2m^-2h^-1,contributed 34% to soil respiration. During the experiment period, Kobresia humilis meadow and Potentilla fruticosa scrub meadow had a net carbon fixation of 111.11 gm^-2 and 243.89 gm^-2 respectively. Results also showed that soil temperature was the main factor which influenced CO2 emission from alpine meadow ecosystem, significant correlations were found between soil temperature at 5 cm depth and CO2 emission from GG, GC, FC and FJ treatments. In addition, soil moisture maybe the inhibitory factor of CO2 emission from Kobresia tibetica meadow, and more detailed analyses should be done in further research  相似文献   

Osmium isotope geochemistry in the Mackenzie River basin     

Youngsook Huh  Jean-Louis Birck 《Earth and Planetary Science Letters》2004,222(1):115-129

The Cenozoic marine osmium isotope record is largely driven by changes in the continental input. We aid its interpretation by supplying direct measurements of present day riverine Os in known geological and environmental settings. We analyzed Os concentrations and isotopic ratios in the dissolved, suspended, and bed materials of the Mackenzie River in Canada and smaller rivers draining the Western Cordillera into the Pacific Ocean. Rhenium content was measured for suspended and bed materials to provide further constraint. Dissolved ¹⁸⁷Os/¹⁸⁸Os ratios range from 0.74 to 4.5 and are controlled to first order by age and lithology of the bedrock. The rivers draining Jurassic volcanic rocks are unradiogenic, as low as 0.74, and those draining the Precambrian Canadian Shield are radiogenic, as high as 3.5. The headwaters of the Mackenzie left bank tributaries draining metamorphic carbonates in the Eastern Cordillera and Paleozoic black and gray shales in the Transition zone and the Interior Platform are especially radiogenic (3.0-4.5) with relatively high concentrations of Os. These latter rivers are responsible for the Mackenzie being above world average in Os concentration and yield (mol Os/km²/year) as well as in ¹⁸⁷Os/¹⁸⁸Os. The dissolved load is more radiogenic than the suspended or bed loads and constitutes a significant fraction of total fluvial Os.  相似文献