Mössbauer study of a California desert celadonite and its pedogenically-related smectite

Celadonite from the northwestern Mojave Desert area of California was examined by detailed Mössbauer spectroscopy at temperatures from 10 K to 400 K. In addition to the predominant Fe³⁺ doublet with isomer shift 0.4 mm s^–1 and quadrupole splitting 0.4 mm s^–1, another Fe³⁺ doublet with 0.4, 1.2 mm/s and two Fe²⁺ doublets with 1.1, 1.7, 2.7 mm s^–1 at 300 K were distinguished. The minor Fe³⁺ component is ascribed to dehydroxylated surface sites. Most of the remaining Fe(90%) is M2 cis-OH octahedral in an ordered M⁺–M²⁺ array. However, about 10% is M1 trans-OH Fe²⁺. Isomer shift vs. T gives Debye temperatures of 570 K for Fe³⁺ in M2 and 380 K for both Fe²⁺ sites, indicating greater vibrational freedom for Fe²⁺. Quadrupole splitting vs. T for Fe²⁺ gives a valence electronic energy splitting of 760 cm^–1 between the ground and first excited state for M2. The M1 sites have a more drastic variation in vs. T which indicates not only a lower first excited state but a rhombic distortion at these sites. A proposed explanation is a neighboring M2 site vacancy. The soil clay formed from this celadonite, which is mostly Fe-rich smectite, was also studied by Mössbauer spectroscopy. About half the Fe²⁺ has been oxidized in the clay, but the isomer shifts and quadrupole splittings are essentially the same as in the original celadonite. A texture orientation in the clay absorber was detected by measuring the absorber at 55° to the source radiation. This texture effect produces asymmetric doublets in the usual 90° measurement.     

Thrust tectonics in the south central pyrenees

Surface structural data and published stratigraphies are combined to construct two balanced and restored sections through the Nogueras Zone of the south central Pyrenees. The allochthonous Nogueras Zone units are interpreted as the foreland-dipping margin of a major antiformal stack in the Palaeozoic rocks of the Pyrenean Axial Zone. Their structural evolution is summarized in a hangingwall sequence diagram. This reinterpretation of the Nogueras Zone is incorporated into a new NS balanced and restored section from the centre of the Pyrenean Axial Zone to the Ebro Basin. A classical ‘Rocky Mountains’ piggy-back thrust model is employed and the resulting section is a significant departure from those previously published. It is argued that ‘gravity gliding’ has never been an important mechanism in the Alpine Pyrenees. Section restoration casts doubt on the correlation of the surface expression of the North Pyrenean Fault and the seismically detected Moho step beneath it.     

Constraints and Categories of Vadose Zone Monitoring Devices

Traditional monitoring methods using chemical analysis of ground water samples to detect pollutant migration are being superseded or used in conjunction with innovative approaches. A need to detect pollutants before they reach the water table has drawn interest to vadose (unsaturated) zone monitoring and brought together hydrogeologists, soil scientists and agricultural engineers who have been working on this subject for years.
Recent studies have identified over 50 different types of vadose zone monitoring devices and methods that have optimum utility in varying hydrogeologic settings. In general, measurements made in the vadose zone are trying to define storage, transmission of liquid waste in terms of flux and velocity, and pollutant mobility.
Criteria for the selection of alternative vadose zone monitoring methods are important for the development of site-specific systems. These criteria include: type of site; applicability to new, active, and abandoned sites; power requirements; depth limitations; multiple use capability; type of data collection system; reliability and life expectancy; degree of operational complexity; direct versus indirect methods; applicability to alternate media; effect on flow regime; and effect of hazardous waste on sampling or measurements. Application of the selection criteria is discussed in Everett et al. (1982a).     

Gossan profiles developed above stratabound sulphide mineralization

Gossan formation is the product of complex interactions of weathering history, present climate, geomorphology, type of mineralization and nature of host rocks. The resultant structure, texture, mineralogy and geochemistry of surface gossans differ markedly even within the one outcrop. Extensive research since 1970 has delineated techniques for evaluating gossans related to nickel mineralization in the Yilgarn Block of Western Australia using these properties. Until recently, similar techniques were not well developed for the search for copper, lead and zinc mineralization.     

Public participation in policy making: the state-of-the-art in Canada

This paper critically reviews the current status of public participation in Canada. Postulating that public participation implies an open, democratic form of planning and policy making, the paper examines factors which have influenced the attainment of meaningful public input in practice. Public participation in Canada has evolved greatly in the past 15 years but several key issues remain unresolved: provisions for participation remain, in large part, discretionary; procedures for the funding of intervenors require further development; and the emphasis in many jurisdictions remains upon the operational level involvement of the lay public, with a public hearing as the final arbiter of public opinion. More attention to the formal evaluation of participatory exercises is essential to the resolution of these concerns. In particular, more attention should be given to the context within which participation occurs. Moreover, greater consideration should be given to public involvement at the normative and strategic levels of planning. The paper concludes by briefly exploring the implications for practice that the concept of ‘normative participation’ might have in Canada.     

Interpretation of vector magnetograph data including magneto-optic effects

In this paper, the presence of Faraday rotation in measurements of the orientation of a sunspot's transverse magnetic field is investigated. Using observations obtained with the Marshall Space Flight Center's (MSFC) vector magnetograph, the derived vector magnetic field of a simple, symmetric sunspot is used to calculate the degree of Faraday rotation in the azimuth of the transverse field as a function of wavelength from analytical expressions for the Stokes parameters. These results are then compared with the observed rotation of the field's azimuth which is derived from observations at different wavelengths within the Fei 5250 Å spectral line. From these comparisons, we find: the observed rotation of the azimuth is simulated to a reasonable degree by the theoretical formulations if the line-formation parameter η _o is varied over the sunspot; these variations in η _o are substantiated by the line-intensity data; for the MSFC system, Faraday rotation can be neglected for field strengths less than 1800 G and field inclinations greater than 45°; to minimize the effects of Faraday rotation in sunspot umbrae, MSFC magnetograph measurements must be made in the far wings of the Zeeman-sensitive spectral line.     

Photometry and polarimetry of Jupiter at large phase angles: I. Analysis of imaging data of a prominent belt and a zone from pioneer 10

Limb-darkening curves are derived from Pioneer 10 imaging data for Jupiter's STrZ (?18 to ?21° latitude) and SEBn (?5 to ?8° latitude) in red and blue light at phase angles of 12, 23, 34, 109, 120, 127, and 150°. Inhomogeneous scattering models are computed and compared with the data to constrain the vertical structure and the single-scattering phase functions of the belt and the zone in each color. The very high brightness observed at a 150° phase angle seems to require the presence of at lleast a thin layer of reasonably bright and strongly forward-scattering haze particles at pressure levelsof about 100 mbar or less above both belts and zones. Marginally successful models have been constructed in which a moderate optical thickness (τ ≥ 0.5) of haze particles was uniformly distributed in the upper 25 km-amagats of H₂. Excellent fits to the data were obtained with models having a thin (optical depths of a few tenths) haze conentraated above most of the gas. Following recent spectrospcopicanalyses, we have placed the main “cloud” layer or layers beneath about 25 km-amagats of H₂, although successful fits to our continuum data probably could be achieved also if the clouds were permitted to extend all the way up to the thin haze layer. Similarly, below the haze level our data cannot distinguish between models having two clouds separated by a clear space as suggested by R. E. Danielson and M. G. Tomasko and models with a single extensive diffuse cloud having an H₂ abundance of a few kilometer-amagats per scattering mean free path as described by W. D. Cochran. In either case, the relative brightness of the planet at each phase angle primarily serves to constrain the single-scattering phase functions of the Jovian clouds at the corresponding scattering angles. The clouds in these models are characterized by single-scattering phase functions having strong forward peaks and modest backward-scattering peaks, indicating cloud particles with dimensions larger than about 0.6 μm. In our models, a lower single-scattering albedo of the cloud particles in the belt relative to the zone accounts for the contrast between these regions. If an increased abundance of absorbing dust above uniformly bright clouds is used to explain the contrast between belts and zones at visible wavelengths, the limb darkening is steeper than that observed for the SEBn in blue light at small phase angles. The phase integral for the planet calculated for either the belt or the zone model in either color lies in the range 1.2 to 1.3. If a value of 1.25 is used with D.J. Taylor's bolometric geometric albedo of 0.28, the planet emits 2.25 or 1.7 times the energy it absorbs from the Sun if it effective temperature is 134 or 125°K, respectively—roughly as expected from current theories of the cooling of Jupiter's interior.     

A Re–Os isotope and PGE study of kimberlite-derived peridotite xenoliths from Somerset Island and a comparison to the Slave and Kaapvaal cratons

The concentrations of platinum-group elements (PGE; Os, Ir, Ru, Pd and Pt) and Re, and the Os isotopic compositions were determined for 33 lithospheric mantle peridotite xenoliths from the Somerset Island kimberlite field. The Os isotopic compositions are exclusively less radiogenic than estimates of bulk-earth (¹⁸⁷Os/¹⁸⁸Os as low as 0.1084) and require a long-term evolution in a low Re–Os environment. Re depletion model ages (T_RD) indicate that the cratonic lithosphere of Somerset Island stabilised by at least 2.8 Ga, i.e. in the Neoarchean and survived into the Mesozoic to be sampled by Cretaceous kimberlite magmatism. An Archean origin also is supported by thermobarometry (Archean lithospheric keels are characterised by >150 km thick lithosphere), modal mineralogy and mineral chemistry observations. The oldest ages recorded in the lithospheric mantle beneath Somerset Island are younger than the Mesoarchean (>3 Ga) ages recorded in the Slave craton lithospheric mantle to the southwest [Irvine, G.J., et al., 1999. Age of the lithospheric mantle beneath and around the Slave craton: a Rhenium–Osmium isotopic study of peridotite xenoliths from the Jericho and Somerset Island kimberlites. Ninth Annual V.M. Goldschmidt Conf., LPI Cont., 971: 134–135; Irvine, G.J., et al., 2001. The age of two cratons: a PGE and Os-Isotopic study of peridotite xenoliths from the Jericho kimberlite (Slave craton) and the Somerset Island kimberlite field (Churchill Province). The Slave–Kaapvaal Workshop, Merrickville, Ontario, Canada]. Younger, Paleoproterozoic, T_RD model ages for Somerset Island samples are generally interpreted as the result of open system behaviour during metasomatic and/or magmatic processes, with possibly the addition of new lithospheric material during tectono-thermal events related to the Taltson–Thelon orogen. PGE patterns highly depleted in Pt and Pd generally correspond to older Archean T_RD model ages indicating closed system behaviour since the time of initial melt extraction. Younger Proterozoic T_RD model ages generally correspond to more complex PGE patterns, indicating open system behaviour with possible sulfide or melt addition. There is no correlation between the age of the lithosphere and depth, at Somerset Island.     

Particle orientation and its influence on the mechanical behaviour of isotropically consolidated reconstituted clay

The behaviour of naturally occurring geological materials such as clay and sand depends on many factors. For example, stresses, strains, previous stress history, mineralogy and the depositional environment all contribute in some degree to a characteristic that all natural soils share, namely “structure”. The structure of clay, or more generally, the microstructure of microscopically sized clay mineral particles, is just as important as the many other parameters that are used to quantify the performance of clays. This paper examines the microstructure that results from the particle arrangement brought about during reconstitution in the laboratory and considers its relevance to the resulting stress–strain behaviour.

Samples of reconstituted kaolin clay were produced using two different procedures. In the first series of tests, kaolin slurry was simply isotropically compressed in one increment. In the second series, the slurry was first isotropically compressed to a low pressure and then completely remoulded. This was followed by isotropic compression to the same pressure as the other series. Specimens were taken from the two series of samples, reconsolidated at various isotropic pressures, and sheared under undrained conditions.

Scanning Electron Microscope (SEM) images indicated that the monotonically compressed samples (Series 1) exhibited an anisotropic microstructure that was distinct from the remoulded (Series 2) samples. Significant differences were also found in the consolidation and stress–strain characteristics of the samples produced in the two series.