Grain boundary migration of water and carbon dioxide during uplift of garnet-zone Alpine Schist, New Zealand

Abstract Deformed quartz veins in garnet-zone schist adjacent to the active Alpine Fault, New Zealand, have fluid inclusions trapped along quartz grain boundaries. Textures suggest that the inclusions formed in their present shapes during annealing of the deformed veins. Many of the inclusions are empty, but some contain carbon dioxide with densities that range from 0.16 to 0.80 g cm⁻³. No water, nitrogen or methane was detected. The inclusions are considerably more CO₂-rich than either the primary metamorphic fluid (<5% CO₂) or fluids trapped in fracture-related situations in the same, or related, rocks (<50% CO₂). Enrichment of CO₂ is inferred to have resulted from selective migration (wicking) of saline water from the inclusions along water-wet grain boundaries after cooling-induced immiscibility of a water-CO₂ mixture. Inclusion volumes changed after loss of water. Non-wetting CO₂ remained trapped in the inclusions until further percolation progressively removed CO₂ in solution. This mechanism of fluid migration dominated in ductile quartz-rich rocks near, but below, the brittle-ductile transition. At deeper levels, hydraulic fracturing is also an important mechanism for fluid migration, whereas at shallower levels advection through open fractures dominates the fluid flow regime.     

Arrested charnockite formation at Kottavattam, southern India

Abstract At Kottavattam, southern Kerala (India), late Proterozoic homogeneous leptynitic garnet–biotite gneisses of granitic composition have been transformed on a decimetric scale into coarse-grained massive charnockite sensu stricto along a set of conjugate fractures transecting the gneissic foliation. Charnockitization post-dates the polyphase deformation, regional high-grade metamorphism and anatexis, and evidently occurred at a late stage of the Pan-African tectonothermal history. Geothermobarometric and fluid inclusion data document textural and chemical equilibration of the gneiss and charnockite assemblages at similar P_lith–T conditions (650–700°C, 5–6 kbar) in the presence of carbonic fluids internally buffered by reaction with graphite and opaque mineral phases (X_CO2= 0.7–0.6; X_H2O= 0.2–0.3; X_N2= 0.1; log f_O2= -17.5). Mineralogical zonation indicates that charnockitization of the leptynitic gneiss involved first the breakdown of biotite and oxidation of graphite in narrow, outward-migrating transition zones adjacent to the gneiss, followed by the breakdown of garnet and the neoblastesis of hypersthene in the central charnockite zone. Compared to the host gneiss, the charnockite shows higher concentrations of K, Na, Sr, Ba and Zn and lower concentrations of Mg, Fe, Ti, V, Y, Zr and the HREE, with a complementary pattern in the narrow transition zones of biotite breakdown. The P_lith–T–X_H2O data and chemical zonation patterns indicate charnockitization through subsolidus-dehydration reaction in an open system. Subsequent residence of the carbonic fluids in the charnockite resulted in low-grade alteration causing modification of the syn-charnockitic elemental distribution patterns and the properties of entrapped fluids. We favour an internally controlled process of arrested charnockitization in which, during near-isothermal uplift, the release of carbonic fluids from decrepitating inclusions in the host gneiss into simultaneously developing fracture zones led to a change in the fluid regime from ‘fluid-absent’in the gneiss to ‘fluid-present’in the fracture zones and to the development of an initial fluid-pressure gradient, triggering the dehydration reaction.     

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.     

Re-scaling collective bargaining: union responses to restructuring in the North American auto industry

Historically, political struggles to define the geographical scale at which labour relations and collective bargaining will be conducted have been of crucial significance to the labour movement. Today, workers and their unions face very difficult challenges. In many manufacturing industries changes in the organizational structure of production at different geographical scales have undermined the effectiveness of the organizing and collective bargaining strategies associated with traditional industrial unionism. This paper focuses on collective bargaining strategies developed by North American autoworkers’ unions to respond to the extensive restructuring of the automotive industry that took place during the 1990s. These strategies include innovations in the structure and content of collective bargaining and efforts to redefine the scale at which collective bargaining takes place. Following a brief discussion of the challenge posed by the integration of Mexico into a continent-wide production system, the analysis focuses on the strategies devised by the Canadian Auto Workers (CAW) union during the 1996 and 1999 rounds of collective bargaining to address issues raised by outsourcing and modular manufacturing. With outsourcing, the automakers are not so much eliminating jobs as they are deciding who gets to do them, at what price, and under what working conditions. With modular manufacturing, the organizational boundaries between firms are blurring and the terms and conditions of work in one firm arguably are becoming dependent upon management decisions made in another firm. The CAW’s response has been to develop new collective bargaining strategies including the concepts of ‘work ownership’ and ‘satellite bargaining’ which involves redefining the traditional geographical extent of the bargaining unit. While the empirical focus is on the North American automobile industry, the general issues related to the re-scaling of production, and especially outsourcing and modular manufacturing, are common across a range of manufacturing industries.     

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.     

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.