Alkali ion migration in albite and K-feldspar

As part of a study of ion migration mechanisms in feldspars, the dynamical behaviour of the alkali metal cations ions in albite and K-feldspar has been investigated using a combination of dielectric spectroscopy and atomistic computer simulation techniques. The low-frequency dielectric properties of these minerals have been studied from room temperature to 1100 K. At each temperature, the dielectric constant, conductivity and dielectric loss were determined over a range of frequencies from 100 Hz to 10 MHz. At high temperatures a distinct Debye-type relaxation in the dielectric loss spectra was observed for both albite and K-feldspar; the activation energy for these processes was determined to be 1.33 eV in both albite and K–feldspar. Atomistic simulation techniques were used to elucidate the mechanism and energetics of the cation migration processes. Mechanisms involving the conventional hopping of Na⁺ and K⁺ ions between cation sites in the (010) plane were found to give calculated energy barriers in good agreement with the experimentally determined activation energies. These results assist in understanding the nature of the processes responsible for the observed dielectric behaviour.     

Challenges of calculating dunefield mobility over the 21st century

Attention has been directed towards both the impacts of future climate change on environmental systems and dunefield activity in the past, but there has been relatively little consideration of potential dune mobility in a future and possibly warmer world. This paper considers the use and limitations of four Global Circulation Models (GCMs) (Hadcm3, Hadcm2, CSIRO-mk2b and CGCM1), in combination with simple dune mobility indices to predict the activity of the Kalahari dunefield. It is clear that uncertainties surround GCM resolution and accuracy, mobility index robustness for the calculation of intra-annual dune mobility and data collection for mobility index calibration. Macro-scale studies that look at large areas of the world over long time scales are well suited to GCM and mobility index use, but dune mobility can be variable within a dunefield, and it is the extreme sand transporting events, occurring at high temporal resolutions, that are the most important for short term studies. To investigate intra-annual changes in dune mobility over a specific dunefield techniques such as downscaling, weather generators and probability curve fitting can help provide climate predictions for smaller areas over shorter time frames. However, these methods introduce uncertainty of their own, and they often rely on the accuracy of original GCM predictions or the climate parameter relationships observed at present. Analysis of intra-annual changes also requires mobility indices that can model monthly mobility patterns well, although existing indices have only been used for calculating annual dune mobility potential. When they are used for intra-annual predictions, the lack of lag response between precipitation decreases and the assumed vegetation dieback leads to an exaggerated amplitude pattern of dune mobility throughout the year. Calibration of dune mobility indices to dune mobility observed on the ground is therefore important but is hampered by a lack of observed measurements for individual months. Solutions are available to overcome some of the outlined problems, but they can provide their own set of uncertainties, which combine to further reduce the confidence given to future dune mobility predictions.     

Mobility of a remobilised parabolic dune in Kennemerland, The Netherlands

A parabolic dune in the Netherlands was remobilised in December 1998 by removing vegetation and soil. The main aim of the experiment was ecological: to investigate whether permanent rejuvenation at the landscape scale is possible by restoration of natural processes. If processes can be reactivated at coarse scale, periodic rejuvenation of the landscape over the long term is possible, without the need for managers to interfere further. The experiment provides the opportunity to address another important question: can large parabolic dunes in the Netherlands be mobile in the present climate? Mobility of the dune is investigated by means of erosion pins, aerial photography and measurement of cross sections. Activity indices are derived from erosion pin recordings and correlated to weather conditions. From 1999 to 2001, displacement of the dune ranged from 0 to 12 m in east–northeasterly direction. Activity of the dune is related to wind conditions, but the relationship is strongly influenced by precipitation and therefore differs for wet and dry periods. Periods with extreme wind speeds resulted in much less geomorphic change than expected.     

首尔都市区的人口迁居及对中国的启示

中国目前已进入快速的工业化和城市化时期,人口迁居在我国大都市区显得越来越重要。韩国在1960年代开始大量的乡村人口迁移到城市地区,进入1970年代,出现了郊区化现象。首先分析了韩国人口迁居的一般特征,接着从就业机会、住房供给和区域政策三方面分析了影响韩国人口迁居的因素,最后针对我国的具体实际,结合韩国的研究提出了几点建议。     

Correlation of rhyolitic pyroclastic eruptive units from the Taupo volcanic zone by Fe–Ti oxide compositional data

Grain-specific analyses of Fe–Ti oxides and estimates of eruption temperature (T) and oxygen fugacity (fO₂) have been used to fingerprint rhyolitic fall and flow deposits that are important for tephrostratigraphic studies in and around the Taupo volcanic zone of North Island, New Zealand. The analysed Fe–Ti oxides commonly occur in the rims of orthopyroxene crystals and appear to reflect equilibrium immediately prior to eruption because of geochemical correlation with the co-existing glass phase. The composition of the spinel phase is particularly diagnostic of eruptive centre for post-65 ka events and can be used to distinguish many tephra beds from the same volcano. The 29 different units examined were erupted over a wide range in T (690–990°C) and Δ log fO₂ (–0.1 to 2.0). These parameters are closely related to the mafic mineral assemblage, with hydrous mineral-bearing units displaying higher fO₂. Such trends are superimposed on larger differences in fO₂ that are related to eruptive centre. At any given temperature, all post-65 ka Okataina centre tephra have higher fO₂ values than post-65 ka Taupo centre tephra. This provides a useful criterion for identifying the volcanic source. There are no temporal T and fO₂ trends in the tephra record; over intervals >20 ka, however, tephra sequences from Taupo centre form characteristic T-fO₂ buffer trends mirroring the glass chemistry. Individual eruptive events display uniform spinel and rhombohedral phase compositions and thus narrow ranges in T (± <20°C) and log fO₂ (± <0.5), allowing these features to identify individual magma batches. These criteria can help distinguish tephra deposits of similar bulk or glass composition that originated from the same volcano. Distal fall deposits record the same T-fO₂ conditions as the proximal ignimbrite and enable distal–proximal correlation. Lateral and vertical compositional and T-fO₂ variability displayed in large volume (>100 km³) ignimbrites, such as the Oruanui, Rotoiti and Ongatiti, is similar to that found in a single pumice clast and thus mainly reflects analytical error; however, thermal gradients of ca. 50°C may occur in some units. Received: 6 April 1998 / Accepted: 16 June 1998     

地电化学提取法的理论与实验研究

根据离子溶液电化学的基本性质和稳定电流场的基本理论,通过理论计算和物理模拟实验,指出：离子在外电场作用下,由所在地点迁移至接收电极所需时间与多种因素有关,当外界条件一定时,加大供电电流强度可减少接收时间;离子淌度值很小,由实测时量曲线计算出的ｕｉ值,一般不超过几个ｃｍ２·ｈ－１·Ｖ－１单位,因此欲提取深部离子,即使在最有利条件下也是非常困难的;由不同供电电流强度测出的时量曲线,计算得到的淌度值是相等的,因此改变供电电流强度并不能改变离子淌度值,但当围岩介质的颗粒度较大时,可使离子淌度值变大;离子的迁移质量与供电电量Ｑ＝Ｉ·ｔ成正比,因此在供电电流强度不变的条件下,采用间断供电方式可取得与连续供电相同的结果;通过浅部已存在的离子晕,用电提取法可以发现深部隐伏矿体。     

AMERICAN ROADS,ROADSIDE AMERICA*

ABSTRACT. Federal support for planning and building roads provided an opportunity to create a new kind of place, the American roadside. The roadside grew up beside the public road as a distinct private space, yet the two were linked as road travelers came to depend on the services provided by people who lived at the road's edge. Federal road-improvement legislation brought discipline to the surveying, construction, and configuration of roads. But roadside structures remained largely the creation of local people, who built a vernacular landscape that was undisciplined and in strong contrast to the road's regimentation. The roadside became a new kind of space occupying the unstable zone between the discipline of the road and the informality of the countryside, a spatial contradiction that gave license to a new, free-wheeling, mercantile logic, an improvisational departure from the staid formality of Main Street.     

黑云母温度计能否用于估计花岗质侵入岩的结晶温度？

为了探讨黑云母温度计是否适用于估计花岗质侵入岩的结晶温度,汇编了国内外典型花岗质侵入体的岩石化学和矿物化学数据,利用Henry等(2005)的黑云母Ti饱和温度计、Li 和Zhang (2022)的黑云母全组分温度计估算了岩浆温度,并与Shao等(2020)的锆饱和温度计估算结果进行了对比。结果表明,黑云母Ti饱和温度计估算的温度比锆饱和温度计和黑云母全组分温度计低50~200℃,因此认为黑云母Ti饱和温度计并不适用于估算花岗质侵入岩的结晶温度,而黑云母全组分温度计可以复现S型和I型花岗岩的锆饱和温度计结果。     

Uranium pollution of South African streams – An overview of the situation in gold mining areas of the Witwatersrand

During more than a century of gold mining in South Africa large amounts of tailings were produced, which now cover vast areas in densely populated regions. These dumps contain elevated levels of uranium and other toxic heavy metals associated with gold in the mined ore. Large-scale extraction of uranium from auriferous ore only took place during the cold war, leaving tailings with high uranium concentrations that were deposited before and after this period. Recent studies found elevated levels of the radioactive heavy metal in groundwater and streams, mainly attributed to the discharge of contaminated water from mines. In this paper the contribution of seepage from slimes dams to the uranium pollution of adjacent streams is analysed. Based on geochemical analyses of samples, field observations and long-term in situ measurements of hydraulic and hydrochemical parameters at selected mining sites across the Witwatersrand goldfields, the extent, mechanisms and dynamics of diffuse stream contamination by tailings seepage is characterised. Temporal and spatial variations of the process and the associated hazard potential are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Current state of research on flow failure considering void redistribution in liquefied deposits

In liquefied ground, lateral flow is sometimes much larger than surface settlement and may exceed several meters even in a gentle slope of less than a few percent. It occurs not only during but also after earthquake shaking. Conventional laboratory soil tests using uniform sand cannot reproduce this phenomenon. Its mechanism is still poorly understood. In this paper, there is a major focus on the mechanism involving void redistribution or water film effects in layered sand deposits using recent findings obtained by different researchers on void redistribution and the associated lateral flow movement that potentially occurs in layered sand deposits. 1G shake table tests, 1D tube tests, torsional simple shear tests, in situ soil investigations, case history studies, etc. are used to develop an understanding of the lateral flow mechanism during liquefaction. Some of the major findings are; sand deposits in the field consist of sublayers with different particle sizes and permeability and readily develop water films by post-liquefaction void redistribution at sublayer boundaries. The water films may have served as sliding surfaces for large flow during the 1964 Niigata earthquake without the constraint of the dilatancy effect because the water films serve as shear stress isolators. The potential of this type of flow failure will be high for loose sand with relative density around 40% or less.