Influence of the Load Wavelength on the Permeability of a Viscosity Interface in the Mantle

Assuming a radially stratified Newtonian mantle in a steady-state approximation, we demonstrate that the permeability of a viscosity interface at 660-km depth strongly depends on the wavelength of buoyancy forces driving the flow. The flow induced by long-wavelength loads penetrates through the boundary freely even if the viscosity increases by two orders. In contrast, the boundary is practically impermeable for short-wavelength loads located in the upper mantle. Thus, a stepwise increase of viscosity is a significant obstacle for small descending features in the upper mantle, but huge upper mantle downwellings, or upwellings formed in the-lower mantle can overcome it easily. This indicates that certain care is necessary in interpreting the seismic structure of the mantle by means of flow models. The global tomographic image includes only the first few degrees of the harmonic series and, consequently, its interpretation in terms of a present-day flow field results in a predominantly whole-mantle circulation even for extreme viscosity contrasts.     

Remote sensing detection of atmospheric pollutants by differential absorption LIDAR 510M/SODAR PA2 mobile system

Summary Air pollution problem in the Czech Republic is very complex due to large number of factors as turbulent dispersion and chemical reactions concurring in the status of the PBL. For this 3D distribution of pollutants is a key information that cannot be given by conventional monitoring stations. Combined use of DIAL lidar and sodar can give access to such information. Case studies of air pollutants transport are presented using 3D concentration fields of NO₂ and ozone measured by lidar and meteorological conditions monitored by Doppler Sodar.     

Geochemical characteristics of mineral air particles emitted inside a clay atomisation plant which introduces waste recycling processes

The objective of this work is to assess the concentrations of three factions of air particles (settable particles, TSP and PM10) and the levels of several toxic elements in a clay atomisation industry through aerosol sampling at several points inside an industrial plant. Mechanical activities, which produce diffuse emissions, are the main process of discharge of particles in both indoor and outdoor workplace environments in the atomisation plant. The levels of As, Cd, Pb, Zn, Ba and Ni increase in the zones with higher concentrations of particles and lower ventilation. The concentrations of As and F are not influenced by the recycling processes. The levels of Cd and Pb do not show great enrichment in air particles collected inside the atomisation plant although the content of both elements is associated with ceramic muck recycling. Finally, the content of B in waste water is mainly transferred in gaseous phase to the atmosphere during the process of drying by atomisation.     

Zircon M127 – A Homogeneous Reference Material for SIMS U–Pb Geochronology Combined with Hafnium,Oxygen and,Potentially, Lithium Isotope Analysis

In this article, we document a detailed analytical characterisation of zircon M127, a homogeneous 12.7 carat gemstone from Ratnapura, Sri Lanka. Zircon M127 has TIMS‐determined mean U–Pb radiogenic isotopic ratios of 0.084743 ± 0.000027 for ²⁰⁶Pb/²³⁸U and 0.67676 ± 0.00023 for ²⁰⁷Pb/²³⁵U (weighted means, 2s uncertainties). Its ²⁰⁶Pb/²³⁸U age of 524.36 ± 0.16 Ma (95% confidence uncertainty) is concordant within the uncertainties of decay constants. The δ¹⁸O value (determined by laser fluorination) is 8.26 ± 0.06‰ VSMOW (2s), and the mean ¹⁷⁶Hf/¹⁷⁷Hf ratio (determined by solution ICP‐MS) is 0.282396 ± 0.000004 (2s). The SIMS‐determined δ⁷Li value is ?0.6 ± 0.9‰ (2s), with a mean mass fraction of 1.0 ± 0.1 μg g^?1 Li (2s). Zircon M127 contains ~ 923 μg g^?1 U. The moderate degree of radiation damage corresponds well with the time‐integrated self‐irradiation dose of 1.82 × 10¹⁸ alpha events per gram. This observation, and the (U–Th)/He age of 426 ± 7 Ma (2s), which is typical of unheated Sri Lankan zircon, enable us to exclude any thermal treatment. Zircon M127 is proposed as a reference material for the determination of zircon U–Pb ages by means of SIMS in combination with hafnium and stable isotope (oxygen and potentially also lithium) determination.     

Reduction of surface subsidence risk by fly ash exploitation as filling material in deep mining areas

The possibility of filling empty underground spaces, which exist owing to the extraction of mineral raw materials, with fly ash and cement fly ash mixes has been studied for the purpose of reducing the impact of deep mining on the surface. The method of physical modelling was used to study the behaviour of fly ash mixes deposited in extracted mine spaces. The models were constructed for two different geometries of underground extracted mine spaces: into cavities of the type of large slits created in the course of mining in steeply lode deposits without subsequently filling the empty space and in vertical shafts of rectangular or circular cross-section with horizontal side headings that have partly caved in due to mine shocks or other seismic events.     

Metamorphic kyanite eclogites in the lufilian arc of Zambia

Eclogites formed by the Lufilian (post-Katanga) metamorphism of gabbros intruded into rocks of the Katanga System (Upper Proterozoic) occur in the Central Province of Zambia. Typical constituents of these rocks are omphacite, almandine garnet with significant contents of the pyrope and grossular components, kyanite and rutile. Eclogites from some localities display well preserved, relict ophitic texture inherited from the original gabbro. Hornblende-scapolite metagabbro and coronite metagabbro often accompany the eclogites, and metalherzolite and serpentinite occur at a few localities. The Zambian eclogites are broadly associated with a variety of relatively high-pressure, kyanite-bearing mineral assemblages some of which are possibly in the eclogite facies. It is suggested that, in addition to temperature and load pressure, fluid pressure, fluid composition (H₂O, CO₂, Cl, SO₃) and permeability of the gabbro due to deformation were important factors for the transformation of gabbro to eclogite in the environment of the Lufilian Arc.     

The study of metal contamination in urban topsoils of Mexico City using GIS

This research presents and discusses information concerning the spatial distribution of heavy metals (Pb, Cu, Zn, Ba, Co, Cr, Ni and V) in the urban environments of Mexico City using geographical information system and statistical analysis. Superficial soil samples (n = 146) were analyzed. The highest contamination indices were found in the north and center zone of the metropolitan area. In contrast, the surrounding rural fields show a lower impact grade. The higher concentrations of Pb, Cu, Zn and Ba were observed as being related to high vehicular traffic, nevertheless other elements such as Co, Cr, Ni and V do not show anthropogenic influence and their content can be attributed to the parental rock. The results are compared with previous surveys carried out in 2003 in order to evaluate temporal deposition trends. No changes were found on reported concentrations except for Cu and Zn, whose concentration has increased in later years. The results suggest that spatial distribution analysis and results in comparison with previous studies could be useful for the management and sustainable development of the metropolitan area of Mexico City.     

The infrared dielectric properties of maghemite, γ-Fe2O3, from reflectance measurement on pressed powders

The infrared complex permittivity functions of three varieties of maghemite, γ-Fe₂O₃, having different degrees of vacancy ordering, have been determined from their IR reflectance spectra, measured at near to normal incidence on pressed powder pellets. The optical constants therefrom obtained have been verified by using them in the simulation of the corresponding absorption spectra for KBr-diluted pellets, and these are in excellent agreement with the experimental spectra. All calculations are based on a procedure for the estimation of the effective dielectric function of a mixture, which incorporates percolation features, recently developed by the authors.