PGE distribution in deformed lherzolites of the Udachnaya kimberlite pipe (Yakutia)

The results of the first study of the PGE distribution in deformed lherzolites of the Udachnaya kimberlite pipe (Yakutia) are presented here. The complex character of evolution of the PGE composition in the Deformed lherzolites is assumed to be the result of silicate metasomatism. At the first stage, growth in the amount of clinopyroxene and garnet in the rock is accompanied by a decrease in the concentration of the compatible PGE (Os, Ir). During the final stage, the rock is enriched with incompatible PGE (Pt, Pd) and Re possible due to precipitation of submicron-sized particles of sulfides in the interstitial space of these mantle rocks.     

Is there a fuelwood crisis in rural Mali?

The study takes a conventional supply and demand approach to the study of fuelwood use. It compares estimated wood production in West African bush and forest formations based on an available equation using rainfall data with own collected data on local wood consumption in a village in southern Mali. To allow comparison, data from 49 other villages in the same area are analysed. This study, toget her with an earlier study in northern Mali, indicates that locally induced deforestation caused by fuelwood use does not represent an immediate problem in rural Mali. Local use of fuelwood does not seem to be exceeding forest regeneration. However, where there is external pressure on the forest represented by commercial exploitation of wood for sale in the urban centres, fuelwood depletion might occur.     

The Role of the Magnetic Field in the Ascension of the 22nd and 23rd Cycles of Activity

The first small active regions of the last two new cycles seem to be formed, in its very first, preparatory stage, close to the equator with uncertain magnetic orientation, and as secondary products at the periphery of equatorial `magnetic bubbles' of the new magnetic flux still belonging to the old cycle. At the real beginning of the new cycle, at the periphery of its higher-latitude `magnetic bubbles', the opposite applies to the secondary regions of the ending cycle. It seems that two modes of magnetic flux supply the visible layers of the photosphere during the cycle transition phase: the emergence of the magnetic flux from the depth of the convective zone, and the mutual interaction of the earlier emerging fluxes, or the action of the `local dynamo', giving rise to the new local magnetic field concentrations.     

Carbon-Oxidizing and Sulfate-Reducing Bacteria in Mozhaisk Reservoir Soils

The population and distribution of carbon-oxidizing and sulfate-reducing bacteria in the soils of the Mozhaisk Reservoir are studied.     

Mean crustal velocity: a critical parameter for interpreting crustal structure and crustal growth

Mean crustal velocity is a critical parameter for genesis of continental crystalline crust because it is a function of mean crustal composition and therefore may be used to resolve continental crustal growth in space and time. Although the best values of mean crustal velocity are determined from wide-angle reflection measurements, most studied here necessarily come from vertical averages in crustal refraction determinations. The mode of 158 values of mean crustal velocity is 6.3 km/s, a velocity which corresponds to a mean crustal composition of granodiorite to felsic quartz diorite; Archean crust may be slightly more mafic. Mean crustal velocities range from 5.8 to 7.0 km/s. The lowest values invariably are found in thermally disturbed rift zones and the highest values correspond to velocities in gabbro. Velocities in island arcs may be as low as 6.0 km/s but are typically 6.5–6.9 km/s which corresponds to andesitic composition; estimates of island arc composition are andesitic. If values of mean crustal velocity are not biased, this observation suggests that continental crust did not grow simply by addition of island arc material. Possibilities are that crust formed from fusion of island arcs and was later changed to more felsic composition by addition of material from the mantle or that the late Archean episode of major crustal growth did not involve processes similar to younger island arcs. Some crustal blocks might be changed in composition and thickness by such processes as underplating, interthrusting, necking and sub-crustal erosion. Specially designed experiments are suggested to determine this parameter so critical for understanding genesis of continental crust.     

A Search for a Globular Cluster whose Passage Through the Galactic Disk Could Induce the Formation of the Gould Belt

The distribution of sites where globular clusters have crossed the Galactic disk during the last 100 million years has been analyzed using the most recent kinematic data for 133 globular clusters (GCs). ThreeGCs (NGC 6341, NGC 7078, and ω Cen) whose distances between the positions where they crossed the Galactic disk and trajectories of the Gould Belt are less than 20% of their heliocentric distances at the crossing time (82, 98, and 96 million years ago, respectively) have been identified. For each of the clusters, this was their next to last, rather than their last, crossing of the Galactic disk. The passage of any one of these three GCs through the disk could potentially have initiated the formation of the Gould Belt.     

Stellar Tomography

I review recent progress in the field of stellar surface imaging, with particular reference to advanced methods for mapping surface-brightness inhomogeneities and the surface vector magnetic field on magnetically active late-type stars. New signal enhancement techniques, utilising profile information from hundreds or thousands of photospheric lines simultaneously, allow images to be derived for stars several magnitudes fainter than was previously possible. For brighter stars, the same techniques make it possible to map features as small as two or three degrees in extent on the stellar surface. This opens up whole new areas of research, such as the ability to use starspot tracking to study surface differential rotation patterns on single and binary stars, and to follow the secular evolution of the magnetic field itself. This revised version was published online in July 2006 with corrections to the Cover Date.     

VELOCITY DISPERSION OF SEISMIC WAVES*

In well velocity surveys made to calibrate Sonic (CV) Logs the calibration survey uses frequencies around 50 Hz whereas the Sonic Logging tool uses frequencies around 20 kHz. There thus exists the possibility of making a direct measure of velocity dispersion. In any one survey the disturbing factors, both instrumental and operational, will often mask any dispersive effect that might exist. Consequently this paper reports on a statistical analysis of the velocity differences resulting from calibration surveys and Sonic logs. Only Borehole Compensated Sonic Logs were used. Four areas were investigated: the North Sea, Abu Dhabi, Libya and Alaska. After rejecting logs and calibration records which were obviously in error there remained 424000 feet (about 130 km) of usable log distributed throughout 66 wells. The four areas were analysed separately and in no case was the estimated dispersion significantly different from zero. However, the mean values did correlate with lithology from (? 0.17 ± 0.18)% for the essentially carbonate section in Abu Dhabi to (+ 0.45 ± 0.25)% for the sand-shale section in Alaska, a positive sign meaning that the higher frequencies travelled faster. Except for Alaska the calibration surveys were made with a wall-clamp geophone, and for these areas amplitude measurements were made. After suitable corrections estimates of the absorption parameter Q were obtained. These varied from 20 to 200 with mean values of 63 for Libya, 70 for Abu Dhabi and 88 for the North Sea (excluding the Tertiary). If, as is usually assumed, the absorption mechanism is linear and is described by a Q which is independent of frequency, then these values would necessarily imply dispersion of several percent. As instanced above no such dispersion was observed. It is possible that the expected dispersion was compensated for by invasion of the mud filtrate into the borehole walls, but it is more likely that the absorption mechanism was substantially non-linear.     

Impacts of primary deforestation upon limestone slopes in northern Vancouver Island, British Columbia

Effects of deforestation upon slopes in limestones and in volcanic rocks in the Benson River valley, northern Vancouver Island, have been investigated quantitatively. Postlogging soil erosion and vegetal regeneration success were assessed by measuring soil depth, percent bare rock and moss cover, and the numbers and diversity of trees, shrubs, and plants on 25 sampling sites, each containing ten measuring quadrats selected at random. Sixteen sites were on the Quatsino Formation, a well-karstified limestone, and nine on the Karmutsen Formation of basaltic lavas. Eight sites were of virgin forest, 16 were logged between 1970 and 1983, and one (on limestone) was logged in 1911. Both bedrock types were significantly affected by the cutting. There was greater loss of soil and an increase in bare rock on the limestones. Erosion was increased significantly by burning on the limestones but not on the volcanics. Within-group comparisons on the limestones determined that steeper slopes and harder burned areas suffered the most and are slowest to regenerate. Volume of timber on the 1911 site was 19 percent of that in similar uncut forest sites. It appears that complete recovery on the barren limestone slopes will require at least some centuries.