Uranium in metamorphic rocks

The distribution of U has been studied in two metamorphic rock-series with a gradient of regional metamorphism. One series ranges from the lowest greenschist to amphibolite facies and the other one shows increasing metamorphic grade from amphibolite to granulite facies. Several medium and high pressure granulitic inclusions from alkali basalts were also analyzed. The abundances of U in the rocks do not appear to be affected by metamorphism below the granulite facies grade. Granulites are depleted in U in comparison with equivalent rocks of amphibolite facies grade. There are also differences in their U distribution, as the bulk of U in amphibolite facies rocks is located along the fractures and cleavage planes of ferro-magnesian minerals and in U-rich accessories, while in granulites, most of the U resides in accessory minerals. It seems that the depletion of U in granulites is due to a loss of U which is not located in accessory minerals or in the crystal structure of rock-forming minerals and may also be related to a migration of hydrous fluids, perhaps during dehydration.     

Uranium in spinel peridotite inclusions in basalts from Sardinia

The uranium distribution in spinel peridotite inclusions and their host basalt from Sardinia, Italy, was determined by fission-track mapping. Whole-rock U concentrations range from 14 to 55 ppb. Although the partitioning of U among major silicate phases of the inclusions — olivine, orthopyroxene and clinopyroxene — remains roughly constant, the U content in the minerals is highly variable, e.g. ranging from 27 ppb to 177 ppb in clinopyroxene. The U variation in the minerals shows no apparent correlation with their major element chemistry. Liquid which equilibrated with the assemblages of inclusions with high U content, had U concentrations higher than those found in basaltic rocks. It is suggested that the inclusions were contaminated with a phase strongly enriched in U and subsequently recrystallized. The available data show that spinel peridotite inclusions of basaltic rocks frequently have complex multistage evolution and thus cannot provide a representative picture of the upper mantle radioactivity.     

Lead isotope and trace element composition of K-feldspars from peraluminous granitoids of the Late Devonian South Mountain Batholith (Nova Scotia, Canada): implications for petrogenesis and tectonic reconstruction

The South Mountain Batholith (SMB) of southwestern Nova Scotia (Canada) is a Late Devonian (~375 Ma) composite intrusion, which crops over an area of about 7,300 km². This peraluminous granitoid body consists of rocks ranging from granodiorite through monzogranite and leucomonzogranite to leucogranite that locally host greisen tin-base metal mineralization. K-feldspar displays large compositional variations of trace elements and Pb isotopic ratios, particularly in the highly fractionated rocks. Many variations are consistent with processes of fractional crystallization, but a distinct enrichment of Rb, Li and Cs accompanied by low K/Rb, Ba/Rb, Eu/Eu* and K/Cs ratios point to the role of fluids during the late stages of magmatic evolution. The correlation of Pb isotopic ratios with the enriched elements and their ratios implies that the isotopic variations are an integral part of the evolution of the SMB. Together with well-defined isochronal relationships of Pb systems in the feldspars, the correlation suggests that fractional crystallization accompanied in the late stages by fluid fractionation led to the formation of Li–F-rich leucogranites. Internally derived U-rich fluids fractionated U/Pb ratios, which in turn produced distinct variations of ²⁰⁶Pb/²⁰⁴Pb and ²³⁸U/²⁰⁴Pb ratios in K-feldspars. This implies that the Pb isotopic values of K-feldspar, which have traditionally been used for tectonic reconstructions, might have been modified in many granitic rocks. Thus, only early magmatic K-feldspars, which show no discernible effects of fluid fractionation yield the initial Pb isotopic compositions of the parental granitic magmas and their sources. The data also show that the geochemical characteristics of the leucogranites are the results of magmatic evolution rather than a distinctive source.     

The relation between the heat flow field and the distribution ofP n -wave velocities for the European continent

Summary The dependence of P_n-wave velocities on the heat flow, temperature at the crustmantle boundary and the thickness of the Earth's crust in Europe was investigated in relation to the problem of lateral inhomogeneities in the upper mantle. A map was constructed of the distribution of P_n-wave velocities on the territory of Europe. The relations these investigations yielded, were compared with the results of laboratory experiments and all the results are discussed from the physical point of view. The conclusion drawn is that that temperature and pressure effect provide a sufficient explanation of the observed regional changes of P_n-wave velocities for the European continent.

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On the problem of frequency calibration of induction variometers with large air-core loops

Zusammenfassung Es wird eine Methode für experimentelle Untersuchung der Frequenzkennlinien von Induktionsvariometern mit Aufnahmeschleifen nichttraditioneller Ausmasse beschrieben. Die Grundlage des beschriebenen Verfahrens bildet eine genaue Bestimmung jenes Teils des magnetischen Kraftflusses, der durch die Aufnahmeschleife durchgeht.     

Statistical-dynamical downscaling of wind roses over the Czech Republic

The present study describes a new method for statistical-dynamical downscaling that combines two different approaches, namely, a set of patterns simulated with a numerical flow model and a transformation function used to process both calculated data and measurements at a reference station. The combined method produces wind roses and wind speed histograms at an arbitrary location in the model domain. The inflow wind direction represented the key parameter to define a set of wind field simulations. The other two inflow parameters, namely, thermal stratification and geostrophic wind speed, were derived from corresponding averaged soundings. The results showed that in the Czech Republic, there are areas where wind roses are deformed by the surrounding terrain. The deformations occur in relatively shallow and wide valleys, and they are more sensitive to the inflow wind direction. Calculated wind roses are compared to corresponding observations at 22 synoptic stations. The most frequent wind direction sector in simulations agreed with measurements at 17 stations. The resulting error in frequency in that sector was under 5 % at 10 stations. In general, the main features of the wind roses are modelled well, even at a relatively large distance from the reference station. However, better performance was achieved for smaller distances between reference station and the site. In further studies, a more extensive set of flow patterns with reduced intervals of thermal stratification and wind speed will likely improve calculated wind roses.     

Collapse of loess upon wetting

Feda, J., 1988. Collapse of loess upon wetting. Eng. Geol., 25: 263–269.

The results of a series of tests conducted on loess samples from one locality, tested under the condition of confined and hydrostatic compression are presented and analyzed. The samples are of different water content and saturation and display different degrees of collapse upon wetting.

Based on the experimental results, a collapse surface is depicted and the phenomenon hypothetically generalized for other types of collapse. The structural collapse causes the mechanical behaviour of samples to be more uniform.

The effect of the hydrostatic stress conditions is reflected in the tendency of samples to deform isotropically, although, originally, they are anisotropic. The phenomenon of collapse cannot be explained by the principle of effective stresses.