Trace element geochemistry of scheelite and rutile from metaturbidite-hosted quartz vein gold deposits, Meguma Terrane, Nova Scotia, Canada: genetic implications

Scheelite and rutile from several metaturbidite-hosted gold-bearing quartz vein deposits of the Meguma Terrane of Nova Scotia were analyzed for trace elements including rare earth elements, niobium and tantalum. Scheelites have high concentrations of Sr, Nb, Y and rare earth elements (REE) with bell-shaped chondrite-normalized REE patterns accompanied by both positive and negative Eu anomalies. They also have high Nb/Ta ratios (80–300). Three distinct trace element types of the scheelites are interpreted to reflect chemical differences in the pulses of hydrothermal fluids. Hydrothermal rutiles have high contents of W (up to 4.2 wt.% WO₃), are rich in Ta compared to Nb and have a very low Nb/Ta ratio (~0.3). Hydrothermal fluids which produced both scheelite with a high Nb/Ta and rutile with a low Nb/Ta ratio are an efficient medium for fractionation of this ratio although these two minerals play an important role during the process.     

The Alpine metamorphism in the Simplon area,Switzerland and Italy

The metamorphic rocks of Mesozoic age, found sandwiched between the Pennine nappes of Simplon area, were subjected to a detailed structural-petrological investigation with a view to clarify the nature of the Alpine metamorphism.Preliminary structural works demonstrated the existence of two B-axes — B₁ and B₂ — both being younger than the regional folding and thrusting movements. Of these two, B₁ is restricted to the northernmost belt of the present area and has been imprinted uniformly on the older crystalline rocks of the Aar-Gotthard massif as well as on their Mesozoic sedimentary cover. The B₁-axis, with its usually steeply plunging habit, can be traced southwards upto the northernmost fringe of the Pennine Mesozoic metamorphites. The subhorizontal to weakly plunging B₂-lineation overprints B₁ in the northernmost sector of the region under consideration. Further southwards, it gains rapidly in prominence and becomes the sole linear fabric element. For the most part, B₂ coincides roughly with the axes of the regional large scale folds B₀; but at places the two may deviate from each other appreciably. The overall behaviour of the B-axes is to be seen in the structural map, in which only the statistical maximum of numerous measurements from each locality has been plotted.Zones of progressive regional metamorphism could be roughly delineated over the whole region. The metamorphic grade rises from low greenschist facies in the NW to middle almandine amphibolite facies to the SE. Although the delineation of the metamorphic facies boundaries is only tentative and it is to be expected that future work would refine them, it is firmly believed that the outline of the pattern would not be necessarily modified thereby. By correlating the individual zones of metamorphic facies of underground exposures of Simplon tunnel with the corresponding ones on the facies map, it was possible to determine approximately the lie of the facies boundary surfaces. They transgress cleanly the regional large scale structures in three dimensions in space, proving thereby that the metamorphism took place after the regional folding and thrusting movements died off. Ancillary evidences on this point were derived through a systematic study of oriented thin sections and intensive petrofabric analysis. It was established that the metamorphic recrystallisation and the post-thrusting penetrative movements leading to the origin of the secondary planar and linear fabric elements went on hand in hand, with the former process ultimately outlasting the latter. In fact, the recrystallisation continued long afterwards under a completely static condition and almost all the porphyroblasts were found to have grown at this stage. The regional metamorphism of this area is therefore independent of the penetrative movements due to Alpine orogenesis and owes its origin to the late plutonic actions.Comparison with other areas shows that the Simplon area could be regarded simply as a prototype of the usual case of regional metamorphism. It is concluded that the regional metamorphism in its ideal form is a complex overprinting of an area of previous dislocation metamorphism by a subsequent phase of plutonic metamorphism. Although deformation does not appear to have played an essential rÔle in bringing about appreciable amount of recrystallisation in regional metamorphic rocks, it ought to be regarded as a conditio sine qua non for the same. Indeed, dislocation metamorphism seems to have paved the path to be trodden over later by plutonic metamorphism — the result being crystalline schists, the products of the so called regional metamorphism. The time-honoured term regional metamorphism has got today the sole advantage of being universally understood.     

Palaeocurrent and environmental implications from anisotropy of magnetic susceptibility (AMS): a case study from Talchir and Barakar formations,Raniganj Basin,West Bengal,India

Oriented cylindrical cores of rock samples were collected from the Talchir and Barakar formations of the Lower Gondwana Supergroup of the Raniganj Basin exposed in and around Kalyaneshwari and Maithon areas. The cores (2.54 cm diameter and 2.2 cm height) were studied in the low field anisotropy of magnetic susceptibility (AMS) measurement to determine the nature of magnetic fabrics, to correlate it with the sedimentological characteristics and to determine the palaeocurrent patterns. The results derived from the statistical parameters (especially the q-factor), the shapes of the susceptibility ellipsoids and directional data of the AMS indicate that the magnetic fabrics within the studied units are primary (depositional) and are correlatable form the palaeoenvironmental features. The orientation of the maximum (K₁), intermediate (K₂) and minimum (K₃) susceptibility axes is dispersed on the lower hemisphere equal area diagram rather than strong clusters which is not because of secondary (tectonic) influence but due to the moderate to high-energy environment of deposition of the sediments in the studied units. Based on the q-factor (which is 0.581 for Barakar Formation and 0.565 for Talchir Formation which are both <?0.7), it is suggested the AMS indicates that the imbrication of the K₁ axis is the indicator of palaeocurrent. Also, the magnetic foliation (average value?=?1.255) exceeds the magnetic lineation (average value?=?1.107) and the shape parameter exceeds 0 in most cases pointing towards an oblate fabric. The palaeocurrent in the present study as indicated by the K₁ axis imbrication is very similar in both the units under study and is due SW. However, apart from this precise palaeocurrent direction, there exists a certain degree of randomness of the susceptibility axes which are very clear indication of corresponding depositional environments.     

Fine mode aerosol chemistry over a tropical urban atmosphere: characterization of ionic and carbonaceous species

An extensive aerosol sampling program was conducted during January-December 2006 over Kolkata (22o33?? N and 88o20?? E), a mega-city in eastern India in order to understand the sources, distributions and properties of atmospheric fine mode aerosol (PM_2.5). The primary focus of this study is to determine the relative contribution of natural and anthropogenic as well as local and transported components to the total fine mode aerosol loading and their seasonal distributions over the metropolis. The average concentrations of fine mode aerosol was found to be 71.2?±?25.2???gm^-3 varying between 34.5???gm^-3 in monsoon and 112.6???gm^-3 in winter. The formation pathways of major secondary aerosol components like nitrate and sulphate in different seasons are discussed. A long range transport of dust aerosol from arid and semi-arid regions of western India and beyond was observed during pre-monsoon which significantly enriched the total aerosol concentration. Vehicular emissions, biomass burning and transported dust particles were the major sources of PM_2.5 from local and continental regions whereas sea-salt aerosol was the major source of PM_2.5 from marine source regions.     

Exotic bulk viscosity and its influence on neutron star r-modes

We investigate the effect of exotic matter in particular, hyperon matter on neutron star properties such as equation of state (EoS), mass-radius relationship and bulk viscosity. Here we construct equations of state within the framework of a relativistic field theoretical model. As hyperons are produced abundantly in dense matter, hyperon–hyperon interaction becomes important and is included in this model. Hyperon–hyperon interaction gives rise to a softer EoS which results in a smaller maximum mass neutron star compared with the case without the interaction. Next we compute the coefficient of bulk viscosity and the corresponding damping time scale due to the non-leptonic weak process including Λ hyperons. Further, we investigate the role of the bulk viscosity on gravitational radiation driven r-mode instability in a neutron star of given mass and temperature and find that the instability is effectively suppressed.      

A machine learning forecasting model for COVID-19 pandemic in India

Stochastic Environmental Research and Risk Assessment - Coronavirus disease (COVID-19) is an inflammation disease from a new virus. The disease causes respiratory ailment (like influenza) with...     

Post-stack seismic inversion and attribute analysis in shallow offshore of Krishna-Godavari basin,India

Seismic attributes such as: amplitude envelope, instantaneous phase and cosine of instantaneous phase of 2D post-stack seismic data facilitates structural and stratigraphic interpretation of shallow marine offshore, Krishna-Godavari basin. Two seismic sections namely, X and Y oriented N-S passing through wells W-1 andW-2 respectively are considered for seismic attribute analysis and porosity prediction. The gamma ray log trend indicates deposition of cleaning upward sediment. Coarsening upward, clayey-silty-sandy bodies, making a series of about 50-60 m thickness, have been evidenced from the gamma ray log. An extensional structural style comprising growth faults is associated with the progradational style of deposition. Four seismic zones have been distinguished. These zones differ in amplitude, frequency and continuity of the reflectors. Channel sands of Cretaceous age of Raghavapuram shale are identified in well log, seismic section and its acoustic impedance section. Major stratigraphic horizons along with faults extending to basement are marked with the help of attribute analysis. Porosity is mapped from transformation of acoustic impedance. The shales/unconsolidated sediments measure a high porosity with low impedance and the more porous sands are in an intermediate range. The predicted impedance and porosity values may be erroneous beyond the drilled depth because of non availability of well log data for calibration.