Mineral inclusions in diamonds from the Sputnik kimberlite pipe, Yakutia

The Sputnik kimberlite pipe is a small “satellite” of the larger Mir pipe in central Yakutia (Sakha), Russia. Study of 38 large diamonds (0.7-4.9 carats) showed that nine contain inclusions of the eclogitic paragenesis, while the remainder contain inclusions of the peridotitic paragenesis, or of uncertain paragenesis. The peridotitic inclusion suite comprises olivine, enstatite, Cr-diopside, chromite, Cr-pyrope garnet (both lherzolitic and harzburgitic), ilmenite, Ni-rich sulfide and a Ti-Cr-Fe-Mg-Sr-K phase of the lindsleyite-mathiasite (LIMA) series. The eclogitic inclusion suite comprises omphacite, garnet, Ni-poor sulfide, phlogopite and rutile. Peridotitic ilmenite inclusions have high Mg, Cr and Ni contents and high Nb/Zr ratios; they may be related to metasomatic ilmenites known from peridotite xenoliths in kimberlite. Eclogitic phlogopite is intergrown with omphacite, coexists with garnet, and has an unusually high TiO₂ content. Comparison with inclusions in diamonds from Mir shows general similarities, but differences in details of trace-element patterns. Large compositional variations among inclusions of one phase (olivine, garnet, chromite) within single diamonds indicate that the chemical environment of diamond crystallisation changed rapidly relative to diamond growth rates in many cases. P-T conditions of formation were calculated from multiphase inclusions and from trace element geothermobarometry of single inclusions. The geotherm at the time of diamond formation was near a 35 mW/m² conductive model; that is indistinguishable from the Paleozoic geotherm derived by studies of xenoliths and concentrate minerals from Mir. A range of Ni temperatures between garnet inclusions in single diamonds from both Mir and Sputnik suggests that many of the diamonds grew during thermal events affecting a relatively narrow depth range of the lithosphere, within the diamond stability field. The minor differences between inclusions in Mir and Sputnik may reflect lateral heterogeneity in the upper mantle.     

Fluid inclusion study of the Ballinglen W-Sn-sulphide mineralization, SE Ireland

Scheelite-mineralized microtonalite sheets occur on the SE margin of the end-Caledonian Leinster Granite in SE Ireland. Scheelite, polymetallic sulphides and minor cassiterite occur in veins in the microtonalites, disseminated throughout the greisened microtonalite sheets and in the adjacent wallrocks. Two major mineralized vein types occur in the microtonalite sheets: (1) Scheelite ± arsenopyrite ± pyrrhotite occur in quartz-fluorite veins, generally without a muscovite selvage; (2) Sphalerite ± chalcopyrite ± pyrite ± galena ± cassiterite ± stannite occur in quartz + fluorite veins with a coarse muscovite selvage and are often intergrown with the muscovite. Quartz-hosted fluid inclusions were examined from representative samples of both vein types using petrographic, microthermometric and laser Raman spectroscopic techniques. Three distinct types of fluid inclusions have been recognized. Primary, vapour rich Type 1 inclusions in quartz from the scheelite-mineralized veins are of H₂O-CO₂-CH₄-N₂ ± H₂S ± NaCl composition and formed between 360–530 °C. Primary and secondary, liquid-rich Type 2 fluid inclusions in the base metal sulphide-mineralized veins are of H₂O-CH₄-N₂ ± H₂S-NaCl composition and formed between 340–480 °C. They also occur as pseudosecondary and secondary inclusions in scheelite-mineralized veins. Late dilute, low temperature H₂O-NaCl + KCl fluid inclusions may be related to late-Caledonian convection of meteoric waters around the cooling Leinster Granite batholith. Received: 4 September 1996 / Accepted: 23 May 1997     

Whole-rock and sulfide lead-isotope data from the hydrothermal JADE field in the Okinawa back-arc trough

The mineralization of the active hydrothermal JADE field resembles in many aspects the Kuroko-type mineralization. The JADE field is located in a back-arc graben and is associated with a bimodal volcanism. Lead isotope data from igneous rocks, sediments, and ores further emphasize the similarities with the Kuroko ores and suggest that both sediments and volcanic rocks contributed comparable amounts of lead to the deposit. When compared to the sediments, a much larger volume of volcanic rocks must have contributed lead to the deposit, because of the considerably lower lead concentration of volcanic rocks. In contrast to the crustal type lead of the JADE field and the Kuroko-type sulfide deposits the lead isotope signatures of VMS-type deposits at mid-ocean ridges is distinctly different. In the absence of a sedimentary cover it reflects the composition of the mantle source, whereas in the presence of a sedimentary cover it is either a mixture of mantle and sedimentary lead or it may even be completely dominated by the latter. Received: 5 October 1995 / Accepted: 10 May 1996     

Ophiolite remnants at the eastern margin of the Bohemian Massif and their bearing on the tectonic evolution

Summary Amphibolites are widespread in the eastern part of the Bohemian Massif, east of the South Bohemian Pluton. Based on their geological situation, their metamorphic evolution and their geochemistry, they were separated into three genetically different units: the Rehberg ophiolite, the Buschandlwand amphibolite and the Raabs group. The metamorphic Rehberg ophiolite consists of a ultramafic to mafic plutonic sequence overlain by a gabbro/dike complex and a volcanic section with basaltic, andesitic and rhyolitic volcanics associated with pelitic to psammitic sediments. The entire ophiolite underwent amphibolite facies metamorphism. Rock/MORB normalisation plots and other element ratio plots, such as Ti vs. V or Ta/Yb vs. Th/Yb argue for a supra-subduction zone environment as site of the origin of the Rehberg ophiolite. The Letovice ophiolite in Moravia is structured in a similar way. Geochemically it shows a more MORB like composition but also a distinct tholeiitic island arc group. Although there is no age data for the protolith of both ophiolites, it is believed that they have formed in an oceanic basin separating the Brunovistulian-Moravian block to the east and the Moldanubian block to the west. Possible traces of the continuation of the ophiolites towards the north can be found in the Stare Mesto ophiolites and the ophiolites surrounding the Sowie Gory block in the Sudetes.

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Ophiolitrelikte am ostrand der Böhmischen Masse und ihre bedeutung für die tektonische entwicklung

Zusammenfassung Amphibolite sind in der Böhmischen Masse, östlich des Südböhmischen Plutons weit verbreitet. Ausgehend von ihrer geologischen Position, ihrer metamorphen Entwick lung und ihrer Geochemie lassen sie sich in drei genetisch unterschiedliche Einheiten teilen: den Rehberg Ophiolith, den Buschandlwand Amphibolit und die Raabser Gruppe. Der metamorphe Rehberg Ophiolith besteht aus einer ultramatischen bis mafischen plutonischen Abfolge, die von einem Gabbro/Gangkomplex überlagert wird und einer vulkanischen Folge mit Basalten, Andesiten and Rhyoliten, die mit tonigen und sandigen Sedimenten verknüpft sind. Der gesamte Ophiolithkörper wurde unter amphibolitfaziellen Bedingungen metamorph überprägt. Rock/MORB Diagramme und andere Elementdarstellungen, wie z.B. das Ti vs. V, oder das Ta/Yb vs. Th/Yb Diagramm sprechen für eine Entstehung des Rehberg Ophioliths in einer Suprasubduction Zone. Der Letovice Ophiolith in Mähren weist eine ähnliche Struktur auf. Geochemisch zeigt er stärkere Ähnlichkeiten mit MORB, enthält aber auch Elemente von tholeiitischen Inselbogenbasalten. Auch wenn es für beide Ophiolithe noch keine Protolith-Altersdaten gibt, scheint es dennoch wahrscheinlich, daß sie in einem Ozeanbecken, das den Brunovistulisch-Moravischen Kontinentalblock im Osten vom Moldanubischen Kontinent im Westen trennt, gebildet wurden. Die mögliche Fortsetzung beider Ophiolithe könnten im Norden der Stare Mesto Ophiolith und die Ophiolithe rund um den Sowie Gory Block in den Sudeten darstellen.

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With 7 Figures     

Texture and mineralogy of sediments from the Ganges-Brahmaputra-Meghna river system in the Bengal Basin, Bangladesh and their environmental implications

 The Bengal basin, Bangladesh, represents one of the most densely populated recent floodplains of the world. The sediment flux through the basin is one of the highest on a global scale. A significant portion of this sediment load find its sink in the basin itself because of its lower elevation and frequent flooding. The textural, mineralogical and chemical nature of the sediments thus have an important bearing on the environmental quality of the basin as well as for the Bay of Bengal. The sediment load of the Ganges-Brahmaputra-Meghna (GBM) river system consists exclusively of fine sand, silt and clay at their lower reaches within the Bengal basin, Bangladesh, and is deposited under uniformly fluctuating, unidirectional energy conditions. The sediments have a close simitarity in grain size with the sediments of the surrounding floodplain. The mineral assemblage is dominated by quartz and feldspars. Illite and kaolinite are the major clay minerals, and occur in almost equal proportion in bed sediments. The heavy mineral assemblage is dominated by unstable minerals which are mostly derived from high-rank metamorphic rocks. The characteristic smaller grain-size, i.e. having large surface-to-mass ratios, and the mineralogy of sediments suggests that they are susceptible to large chemical adsorptive reactions and thus could serve as a potential trap for contaminants. However, the sediments of the GBM river system in the Bengal basin, Bangladesh, shows lower concentration of Pb, Hg and As, and a marginally higher value for Cd as compared to that of standard shale. Considering population density and extensive agricultural practice in the basin, the sediments can in the long run become contaminated. Received: 9 November 1994 · Accepted: 18 June 1996     

Political polarization at the national and the intra-urban levels: the role of Moscow in Russian politics and socio-political cleavages within the city

The results of the 1993–1996 national elections in Moscow by administrative districts municipal areas and wards are considered. The author identifies and explains the origins of the principal electoral patterns in the largest and relatively the most prosperous Russian city and interprets them in terms of the relationship between the processes of social and political polarization at the national and the inter-urban levels. He determines the peculiarities of the political views of specific social groups and of residents of various types of housing. Stability and dynamics of the electoral geography is also examined.     

SMLTM simulations of the diurnal tide: comparison with UARS observations

Wind and temperature observations in the mesosphere and lower thermosphere (MLT) from the Upper Atmosphere Research Satellite (UARS) reveal strong seasonal variations of tides, a dominant component of the MLT dynamics. Simulations with the Spectral mesosphere/lower thermosphere model (SMLTM) for equinox and solstice conditions are presented and compared with the observations. The diurnal tide is generated by forcing specified at the model lower boundary and by in situ absorption of solar radiation. The model incorporates realistic parameter-izations of physical processes including various dissipation processes important for propagation of tidal waves in the MLT. A discrete multi-component gravity-wave parameterization has been modified to account for seasonal variations of the background temperature. Eddy diffusion is calculated depending on the gravitywave energy deposition rate and stability of the background flow. It is shown that seasonal variations of the diurnal-tide amplitudes are consistent with observed variations of gravity-wave sources in the lower atmosphere.     

Afternoon mid-latitude current system and low-latitude geomagnetic field asymmetry during geomagnetic storms

For four geomagnetic storms of middle intensity the relationship between the low-latitude magnetic field asymmetry using ASY indices and the intensity of the auroral eastward and westward electro-jet was considered. It was asked whether there exists a connection between ASY and the eastward electrojet. To answer this question equivalent current systems were estimated in mid-latitudes. It was found that the observations obviously show no correlative relationship between the low-latitude magnetic-field asymmetry and the eastward electrojet, whereas one exists between ASY and the westward electrojet. To explain the generally accepted common three-dimensional current system between the partial ring current and the eastward electrojet, a condensor model of the three-dimensional current system was developed. It could be shown that the short periodic variations of the partial ring current are shielded by the condensor and cannot influence the eastward-electrojet current.     

Effect of class-interval size on entropy

The value of Shannon entropy for a given set of data depends on the class interval chosen to compute the relative frequency of each class. For three data sets, expressed in dimensional as well as nondimensional form, the entropy value was computed for different class-interval sizes. Entropy was found to decrease with increasing class interval as well as with increasing sampling interval. It is suggested that these intervals should be selected with care.