Low pressure mineral-melt equilibria in natural anhydrous mafic systems

Contributions to Mineralogy and Petrology - Low pressure phase equilibria for natural mafic systems may be calculated utilizing empirically derived single component distribution coefficients and...     

Uncertainty in Coal Property Valuation in West Virginia: A Case Study

Interpolated grids of coal bed thickness are being considered for use in a proposed method for taxation of coal in the state of West Virginia (United States). To assess the origin and magnitude of possible inaccuracies in calculated coal tonnage, we used conditional simulation to generate equiprobable realizations of net coal thickness for two coals on a 7 min topographic quadrangle, and a third coal in a second quadrangle. Coals differed in average thickness and proportion of original coal that had been removed by erosion; all three coals crop out in the study area. Coal tonnage was calculated for each realization and for each interpolated grid for actual and artificial property parcels, and differences were summarized as graphs of percent difference between tonnage calculated from the grid and average tonnage from simulations. Coal in individual parcels was considered minable for valuation purposes if average thickness in each parcel exceeded 30 inches. Results of this study show that over 75% of the parcels are classified correctly as minable or unminable based on interpolation grids of coal bed thickness. Although between 80 and 90% of the tonnages differ by less than 20% between interpolated values and simulated values, a nonlinear conditional bias might exist in estimation of coal tonnage from interpolated thickness, such that tonnage is underestimated where coal is thin, and overestimated where coal is thick. The largest percent differences occur for parcels that are small in area, although because of the small quantities of coal in question, bias is small on an absolute scale for these parcels. For a given parcel size, maximum apparent overestimation of coal tonnage occurs in parcels with an average coal bed thickness near the minable cutoff of 30 in. Conditional bias in tonnage for parcels having a coal thickness exceeding the cutoff by 10 in. or more is constant for two of the three coals studied, and increases slightly with average thickness for the third coal.     

Investigation of NaCl deliquescence in porous substrates using RH-XRD

We report on the use of X-ray diffractometry under controlled conditions of temperature and relative humidity (RH-XRD) for the investigation of NaCl deliquescence in the pore space of glass filter frits, which were used as model substrates. The study confirms that RH-XRD is an appropriate experimental technique for the in situ observation of phase transformation in porous materials. It is used for an investigation of both the deliquescence kinetics and the deliquescence humidity within pores of different median pore diameter. Several major influences affecting deliquescence rates in the pore space close to the surface of a porous material are discussed. It appears that quite short-term variation of ambient relative humidity, e.g., typical daily fluctuations, might induce damaging deliquescence–crystallization cycles within the pore space of building materials. In agreement with theoretical considerations it was found that confinement of NaCl crystals in pores with median diameters in the range 1.4–70 μm does not affect the deliquescence humidity of the salt.     

Inverse groundwater modelling in the Willunga Basin,South Australia

A new inverse technique for modelling groundwater flow, based on a functional minimization technique, has been used to calibrate a groundwater flow model of a subregion of the Port Willunga aquifer within the Willunga Basin in South Australia. The Willunga Basin is the location of extensive viticulture, irrigated primarily by groundwater, the levels and quality of which have declined significantly over the last 40 years. The new method is able to generate estimates of transmissivity, storativity and groundwater recharge over the whole subregion as a time-varying continuous surface; previous methods estimate local discrete parameter values at specific times. The new method has also been shown to produce accurate head values for the subregion and very good estimates of groundwater recharge. Its ultimate goal will be to provide a new and invaluable tool for significantly improved groundwater resource management. Supported in part by US National Science Foundation grants, DMS-0107492 and DMS-0079478.     

<Superscript>57</Superscript>Fe Mössbauer spectroscopy,X-ray single-crystal diffractometry,and electronic structure calculations on natural alexandrite

Natural alexandrite Al₂BeO₄:Cr from Malyshevo near Terem Tschanka, Sverdlovsk, Ural, Russia, has been characterized by ⁵⁷Fe Mössbauer spectroscopy, electron microprobe, X-ray single-crystal diffractometry and by electronic structure calculations in order to determine oxidation state and location of iron. The sample contains 0.3 wt% of total iron oxide. The ⁵⁷Fe Mössbauer spectrum can be resolved into three doublets. Two of them with hyperfine parameters typical for octahedrally coordinated high-spin Fe³⁺ and Fe²⁺, respectively, are assigned to iron substituting for Al in the octahedral M2-site. The third doublet is attributed to Fe³⁺ in hematite. Electronic structure calculations in the local spin density approximation are in reasonable agreement with experimental data provided that expansion and/or distortion of the coordination octahedra are presumed upon iron substitution. The calculated hyperfine parameters of Fe³⁺ are almost identical for the M1 and M2 positions, but the calculated ligand-field splitting is by far too large for high-spin Fe³⁺ on M1.     

Identification of buried sinkholes using refraction tomography at Ft. Campbell Army Airfield,Kentucky

Karst aquifers are highly susceptible to contamination, with numerous points of entry for contaminants through recharge features such as sinkholes, swallow holes and solutionally enlarged fractures. These recharge features may be filled or obscured at the surface, requiring the use of geophysical or remote sensing techniques for their identification. This study uses seismic refraction data collected at the Ft. Campbell Army Airfield (CAAF), Kentucky, USA, to test the hypothesis that refraction tomography is a useful tool for imaging bedrock depressions beneath thick overburden (greater than 20 m of unconsolidated sediment). Southeast of the main taxiway of CAAF seismic velocity tomograms imaged a bedrock low, possibly a closed depression, at a depth of 25 m that had been earlier identified through delay-time analysis of the same refraction data. Tomography suggests the bedrock low is about 250-m wide by 10-m deep at its widest point. High rates of contaminant vapor extraction over the western extension of this feature suggest a high concentration of contaminants above, and within, this filled bedrock low, the base of which may contain solutionally enlarged fractures (i.e. karst conduits) that could funnel these contaminants to the upper or lower bedrock aquifers. This study thus demonstrates the viability of seismic refraction tomography as a tool for identification of filled sinkholes and bedrock depressions in karst areas.     

A numerically calibrated reference level (MP28) for the terrestrial mammal-based biozonation of the European Upper Oligocene

The fauna of the Enspel (Westerwald) and the neighbouring Kärlich (Neuwied basin) fossil deposits correspond to the Upper Oligocene Mammal Paleogene (MP) reference level 28 and 28–30, respectively. Basaltic flows and a trachyte tuff terminating and predating the fossil deposit sedimentation allow to numerically calibrate the MP reference levels by radioisotope dating. Laser fusion ⁴⁰Ar/³⁹Ar step heating on volcanic feldspars yield a time interval of 24.9–24.5 Ma for reference level MP28 at Enspel and a maximum age of 25.5 Ma for the time interval MP28–MP30 at Kärlich. Interpolation between the time intervals determined for the Enspel reference level MP28 and the age of the global Oligocene/Miocene boundary of 24.0 ± 0.1 Ma taken from literature results in time intervals of 24.5–24.2 Ma and 24.2–23.9 Ma for the younger reference levels MP29 and MP30, respectively. These intervals of ≤ 0.4 m.y. for MP reference levels of the latest Oligocene are short relative to older Oligocene MP reference levels 21–27 between 34 and 25 Ma. Since subdivision into MP reference levels essentially is based on assemblages of mammal taxa and on evolutionary changes in tooth morphology of mammals short MP time intervals during the latest Oligocene indicate a rapid evolutionary change relative to the early Oligocene.     

Migrants, markets and multinationals: competition among world cities for the highly skilled

Urban areas compete with one another for people, goods, capital, ideas and other inputs of economic activity. Under the rubric of globalization, instead of only maintaining or improving the initial stock of assets in a city, the power of a place to attract outside flows of economic activity from elsewhere is increasingly important to economic development. Similarly, global or world cities are characterized as the command and control points through which these global economic flows operate. In response to the heightened mobility of highly-skilled labor across national borders, research has begun to examine the role of international human capital as an economic flow. This paper will examine the role of places in determining where the highly-skilled go in the global economy by viewing global city command and control functions as requiring unique labor flows. By reviewing the evidence found in the literature, we can better understand the potential for urban areas to compete for highly-skilled labor in the global economy. Known indicators of place attractiveness are assessed to examine the relationship between the economic trajectories of cities and their labor requirements. Cities are situated between firms and states as the key place-based actors which influence the mobility of highly-skilled labor. Finally, the paper also examines measurement issues and methodological problems in creating indices of world cities as well as explores possibilities for new research.     

Initiation and growth of salt-based thrust belts on passive margins: results from physical models

Scaled sandbox models simulated primary controls on the kinematics of the early structural evolution of salt‐detached, gravity‐driven thrust belts on passive margins. Models had a neutral‐density, brittle overburden overlying a viscous décollement layer. Deformation created linked extension–translation–shortening systems. The location of initial brittle failure of the overburden was sensitive to perturbations at the base of the salt. Salt pinch‐out determined the seaward limit of the thrust belt. The thrust belts were dominated by pop‐up structures or detachment folds cut by break thrusts. Pop‐ups were separated by flat‐bottomed synclines that were partially overthrust. Above a uniformly dipping basement, thrusts initiated at the salt pinch‐out then consistently broke landward. In contrast, thrust belts above a seaward‐flattening hinged basement nucleated above the hinge and then spread both seaward and landward. The seaward‐dipping taper of these thrust belts was much lower than typical, frictional, Coulomb‐wedge models. Towards the salt pinch‐out, frictional resistance increased, thrusts verged strongly seawards and the dip of the taper reversed as the leading thrust overrode this pinch‐out. We attribute the geometry of these thrust belts to several causes. (1) Low friction of the basal décollement favours near‐symmetric pop‐ups. (2) Mobile salt migrates away from local loads created by overthrusting, which reduces the seaward taper of the thrust belt. (3) In this gravity‐driven system, shortening quickly spreads to form wide thrust belts, in which most of the strain overlapped in time.