Nd-Sr isotopic and trace element study of rocks and fluids from the continental deep drilling Project (KTB), Germany

Geochemical analyses were interpreted on the dominant lithological units and on a deep crustal fluid from the Continental Deep Drilling Project (KTB) Pilot Hole, situated at the western margin of the Variscan Bohemian Massif. The biotite gneiss (from 384 m depth) shows a rare earth element pattern very similar to the European shale composite with Nd model ages of 940 Ma (CHUR) and 1.4 Ga (DM). The lamprophyre dike in the upper profile (1549 m), a nepheline and olivine normative basalt, is geochemically and isotopically similar to rocks from the Tertiary Central European Volcanic Province. The lower metabasite sequence (3575–4000 m), with an intrusion age of approximately 500 Ma, is made up primarily of highly metamorphosed subalkalic olivine basalts. The geochemical characteristics of the metabasites are a (La/Yb)_N of 5–10, an La concentration of 20–50 times chondrite as well as (⁸⁷Sr/⁸⁶Sr)_i of 0.7035–0.7038 and _Nd(T) of 4–6. These values suggest a depleted mantle source for the igneous precursors, evolving by assimilation-fractional crystallization processes with up to 25% of upper crust into the ultramafic, basaltic, and intermediate rock types of the metabasite sequence. The strong geochemical and chronological similarities between the KTB metabasites and rocks from the Münchberg Massif suggest that these units belong to the same lithological complex. The high salinity as well as the radiogenic ⁸⁷Sr/⁸⁶Sr ratio of 0.709413 in the KTB fluid from 4000 m depth might be the result of migrating fluids reacting with the regional Permo-Mesozoic evaporite deposits, followed by extensive Sr isotopic exchange with the upper crust.     

STRUCTURE AND ROTATION OF THE SOLAR INTERIOR: INITIAL RESULTS FROM THE MDI MEDIUM-L PROGRAM

The medium-l program of the Michelson Doppler Imager instrument on board SOHO provides continuous observations of oscillation modes of angular degree, l, from 0 to 300. The data for the program are partly processed on board because only about 3% of MDI observations can be transmitted continuously to the ground. The on-board data processing, the main component of which is Gaussian-weighted binning, has been optimized to reduce the negative influence of spatial aliasing of the high-degree oscillation modes. The data processing is completed in a data analysis pipeline at the SOI Stanford Support Center to determine the mean multiplet frequencies and splitting coefficients. The initial results show that the noise in the medium-l oscillation power spectrum is substantially lower than in ground-based measurements. This enables us to detect lower amplitude modes and, thus, to extend the range of measured mode frequencies. This is important for inferring the Sun's internal structure and rotation. The MDI observations also reveal the asymmetry of oscillation spectral lines. The line asymmetries agree with the theory of mode excitation by acoustic sources localized in the upper convective boundary layer. The sound-speed profile inferred from the mean frequencies gives evidence for a sharp variation at the edge of the energy-generating core. The results also confirm the previous finding by the GONG (Gough et al., 1996) that, in a thin layer just beneath the convection zone, helium appears to be less abundant than predicted by theory. Inverting the multiplet frequency splittings from MDI, we detect significant rotational shear in this thin layer. This layer is likely to be the place where the solar dynamo operates. In order to understand how the Sun works, it is extremely important to observe the evolution of this transition layer throughout the 11-year activity cycle.     

The formation of superdense gaseous cores in the nuclei of disk galaxies: II

In a previous paper (hereafter referred to as Paper I) we have tried to show that superdense cores in the nuclei of disk galaxies can be formed by accretion of gas ejected by the evolved stars which populate the central bulge of these galaxies. Solving the equations for radial flow of a magnetized gas, we found that the accretion of an explodable mass at the core can be achieved over a time-scale ranging from a few times 10⁷ and a few times 10⁸ yr. It was shown, however, that the accretion process is seriously inhibited if the gas possesses sufficient rotational velocity but lacks any dissipative, mechanism within the system. Since rotational velocity is an observed parameter of the stars which shed the gas to be accreted, one must consider the existence of some dissipative force in it in order that the accretion process may be efficient. In the present paper, therefore, we have solved the problem of the flow of a rotating, viscous (variable), magnetized gas. With plausible assumptions regarding some of the parameters involved, the time-scale for the accretion of an explodable mass (10⁹ M ) at the core again turns out to be ranging between a few times 10⁷ and a few times 10⁸yr. Such time-scale has been proposed by several authors as that for repeated explosions in nuclei of these galaxies. It has also been proposed by many authors that the spiral arms are generated and destroyed in disk galaxies over the same time-scale. Our solution also yields a nearly linear rotational velocity law which is usually observed in the central regions of these galaxies.     

Gravitational collapse of cosmic gas clouds and formation of star clusters

In this paper the gravitational collapse of cosmic gas clouds and formation of star clusters has been considered. Hoyle's view of successive fragmentation has been taken as the basic mechanim in the present work. The initial masses of protostars have been estimated as the function of their distances from the centre of the cluster and the intensity of the magnetic field of the medium. It has been shown that the fragmentation process is greatly inhibited by the presence of a strong magnetic field. A model has been constructed showing how a protostar grows in mass by accretion from the surrounding medium, on the basis of the assumption that as the star moves at random in the cluster it picks up a fraction of the material through which it passes. It has been estimated that a protostar of initial mass of about 0.1M grows to one of 1.0M in a time period which ranges from a few multiples of 10⁵ to a few multiples of 10⁷ yr, depending on the parameters involved in the accretion process. The number of stars per unit mass range has also been estimated; it is found to be proportional tom ^–3.3,m being the mass of the star.     

Changing levels of disparity in material well being: highlighting rural urban differentials in West Bengal,India

This study assesses the disparity in the level of material wellbeing between the rural and urban areas of various districts of West Bengal. To measure the level of material wellbeing three broad domains comprising of Housing index (HI), Basic Amenities Index (BAI) and Asset Index (AI) following which a composite index (Material Wellbeing Indexi.e. MWI) was computed for the urban and the rural areas for all the districts between the time frame of 2001–2011. A set of 14 sub-indicators were selected for the analysis. This paper takes into account the differentials between the urban and the rural areas of the state. The data was subjected to correlation analysis, ANOVA and PCA, intra-zonal analysis was also performed. The results show the presence of widespread levels of disparity between the various districts as well as within the districts. Over the course of the years this disparity has increased in case of the northern zone however intra and inter zonal disparity runs high. Among the different sub-indicators, BAI has recorded the highest decrease in the differentials whereas the AI has recorded the highest increase in the differentials. Among the districts eight of them have recorded a net increase in the differentials in MWI among which Maldah has recorded the highest decrease in the differentials whereas Dakshin Dinajpur has recorded the highest increase in the differentials.

     

Impact of SARAL/AltiKa-Derived Sea Level Anomaly in a Data Assimilative Ocean Prediction System for the Indian Ocean

The impact of SARAL/AltiKa derived sea level anomaly (SLA) has been studied by assimilating it along with Jason-2 and Cryosat-2 SLA in the Princeton Ocean model (POM) using ensemble optimal interpolation (EnOI) technique. For isolating the extra benefit brought by SARAKL/Altika, a parallel run with assimilation of only Jason-2 and Cryosat-2 SLA has also been conducted. The importance of SARAL SLA in a data assimilative ocean prediction system has been evaluated with special emphasis on the improvement in thermocline depth, depth of the 20° isotherm, subsurface temperature and currents. Comparison with RAMA buoy has shown a positive impact of up to 13% for 20°C isotherm and up to 17% for thermocline depth after assimilating SARAL SLA. An overall improvement in temperature profile is also observed when compared with analogous profiles from RAMA buoys and Argo floats. Improvement in zonal currents away from the equator has also been noticed.     

Interpreting Helioseismic Structure Inversion Results of Solar Active Regions

Helioseismic techniques such as ring-diagram analysis have often been used to determine the subsurface structural differences between solar active and quiet regions. Results obtained by inverting the frequency differences between the regions are usually interpreted as the sound-speed differences between them. These in turn are used as a measure of temperature and magnetic-field strength differences between the two regions. In this paper we first show that the “sound-speed” difference obtained from inversions is actually a combination of sound-speed difference and a magnetic component. Hence, the inversion result is not directly related to the thermal structure. Next, using solar models that include magnetic fields, we develop a formulation to use the inversion results to infer the differences in the magnetic and thermal structures between active and quiet regions. We then apply our technique to existing structure inversion results for different pairs of active and quiet regions. We find that the effect of magnetic fields is strongest in a shallow region above 0.985R _⊙ and that the strengths of magnetic-field effects at the surface and in the deeper (r<0.98R _⊙) layers are inversely related (i.e., the stronger the surface magnetic field the smaller the magnetic effects in the deeper layers, and vice versa). We also find that the magnetic effects in the deeper layers are the strongest in the quiet regions, consistent with the fact that these are basically regions with weakest magnetic fields at the surface. Because the quiet regions were selected to precede or follow their companion active regions, the results could have implications about the evolution of magnetic fields under active regions.     

Occurrence of Proterozoic black shale-hosted uranium mineralisation in Tal Group,Sirmour district,Himachal Pradesh

Black shale type uranium deposits, though of low grade (<0.001 to 0.05% U₃O₈), contain large uranium resources because of their immense volume. The Neoproterozoic-Cambrian Krol-Tal Himalayan sequence covering a cumulative area of about 1000 sq km in five different synclinal basins from Sirmour district, Himachal Pradesh in the west to Nainital district, Uttar Pradesh in east contain such black shale horizons. The uranium mineralisation found in black shale in the Nigalidhar syncline of Himachal Pradesh and its implication of being an indicator for search of such uranium deposits in Himalayas is discussed.