Thermodynamic properties of Zn(Al,Cr)2O4 spinels at high temperatures and pressures

Three Al-Cr exchange isotherms between Zn(Al, Cr)₂O₄ spinel and (Al, Cr)₂O₃ corundum crystalline solutions have been studied experimentally at 900°, 1100°, and 1300° C, at a total pressure of 25 kbar. Employing data on the equation of state of corundum (Chatterjee et al. 1982), the experimental results were evaluated thermodynamically. It was found that the thermodynamic mixing properties of Zn(Al, Cr)₂O₄ spinels are best described in terms of a symmetric Margules equation. The T- and P- dependence of the Margules Parameter, W _G ^Sp , and of ΔG^* of the exchange reaction, 1/2 ZnAl₂O₄ + 1/2 Cr₂O₃ = 1/2 ZnCr₂O₄+1/2 A1₂O₃, are found to be ΔG ^*=1493?2.869·T+0.0081·P and W _G ^Sp (J/mol)=23456+0.0386·P, with T given in K and P in bar.     

A proposed new approach for groundwater resources assessment in India

Assessment of groundwater resources in India is guided by National Water Policy (1987, 2002) which states that groundwater resources can be exploited only up to its recharge limit. The methodology for groundwater resources assessment in India is broadly based on Ground Water Resources Estimation Methodology, 1997 and it involves assessment of annual replenishable groundwater resources (recharge), annual groundwater draft (utilization) and the percentage of utilization with respect to recharge (stage of development). The assessment units (blocks/watersheds) are categorized based on stage of groundwater development (utilization) and the long term water level trend. The present methodology though useful in identification and prioritization of areas for groundwater management, falls short of addressing several critical issues like spatial and temporal variation of groundwater availability within the aquifer, accessibility of groundwater resources and quality of groundwater. This paper introduces a new categorisation scheme considering the above issues. The proposed scheme takes into account four criteria, viz. (i) stage of exploitation, (ii) extractability factor, (iii) temporal availability factor and (iv) quality factor. In comparison to the existing method used for categorisation, the proposed approach is more inclusive. The methodology is also equally suitable for both alluvial and hard rock terrain since it takes into consideration the variable characteristics of different types of aquifers and convergence of quantitative and qualitative assessment. The categorisation proposed here involves GIS based integration of different parameters/ themes. This allows better representation of spatial variability. The proposed methodology is demonstrated in this paper taking a case study from a hard rock terrain in central India.     

Propagation of love waves in a medium containing a heterogeneous layer lying over a heterogeneous half space

Summary Propagation and the dispersion equation of love waves for a few generalised models of heterogeneous crust over a heterogeneous mantle have been investigated. Dispersion equations obtained by a few earlier authors have been shown to be the special cases of the above results.     

On the disturbances of cylindrical origin in a non-homogeneous isotropic elastic medium

Summary The paper deals with the investigation of disturbances in an infinite non-homogeneous isotropic elastic medium produced by a source operating on the inner surface of a cylindrical hole.     

Time and place of progressive regional metamorphism: A discussion

That in areas of regional metamorphism thermal fronts surging from the depths invade the geosynclinal prism in the waning stage of its deformation and bring about re- and neocrystallization oftener than not outdating the penetrative movements, have been demonstrated time and again from metamorphic terrains of all ages and continents. In the present issue of this journal Dr. K.Naha describes a case from a polymetamorphic complex of Eastern Indian Precambrians, where the metamorphism is pictured to have taken place syn- to posttectonically with reference to the folding movements, regional thrusting following subsequently. It is pointed out that compelling evidence, leading to the conclusion that folding and metamorphism on the one hand and thrusting on the other belong to one and the same cycle of orogeny in his area, is yet to be presented. Such a proof, the onus of which lies withNaha, is indispensable before this unique sequence of regional metamorphism prior to diastrophic paroxysm may be claimed to have been established.

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Zusammenfassung Studien in den verschiedensten Gebieten mit Regionalmetamorphose zeigen immer wieder, daß die metamorphe Kristallisation mit den Durchbewegungen beginnt und sie meist überdauert.Naha (in diesem Heft) beschreibt aus einem polymetamorphen Komplex einen Fall von — bezogen auf die Faltung — synbis posttektonischer Metamorphose, welcher eine regionale Überschiebung folgt. Damit ist aber noch nicht bewiesen, daß alle diese Vorgänge ein und demselben orogenen Zyklus angehören. Eine solche Beweisführung ist unerläßlich, um eine Metamorphose, die vor der Hauptphase der Tektonik stattfindet, glaubhaft erscheinen zu lassen.

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Résumé Des recherches dans les schistes lustrés de la région du Simplon indiquent que de grandes déformations ont suivi la formation des nappes penniques. En même temps que ces déformations, apparaït une métamorphose (recristallisation et néocristallisation) qui dure plus longtemps que les processus tectoniques. Ceci confirme les observations faites dans d'autres régions alpines.Remarques critiques sur le travail deNaha (paru dans ce tome).

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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.     

Pollution of limestone aquifer due to urban waste disposal around Raipur,Madhya Pradesh,India

During the rainy season deterioration in the quality of water, supplied through dug wells and tube wells, near an abandoned limestone quarry was reported. The abandoned quarry is now being used as an urban waste disposal site. The problem was further complicated by hospitalization of several inhabitants who were using this water for domestic purposes. Looking into the consequences, chemical analysis of water from the quarry, dug wells and tube wells was carried out. The water was found to be contaminated. The transportation of pollutants from the quarry to the groundwater system was facilitated by karst features. Furthermore, four major sources—domestic waste disposal, water conservation structures, landfills, and water wells—contributing to pollution were identified. This case study is an attempt to provide an understanding of how the karst features facilitate groundwater contamination. It will help us answer a few questions such as why karst hydrogeology deserves special attention in urban expansion and what protective measures should be planned in view of rapid urbanization.     

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.     

Groundwater arsenic contamination and its health effects in India

During a 28-year field survey in India (1988–2016), groundwater arsenic contamination and its health effects were registered in the states of West Bengal, Jharkhand, Bihar and Uttar Pradesh in the Ganga River flood plain, and the states of Assam and Manipur in the flood plain of Brahamaputra and Imphal rivers. Groundwater of Rajnandgaon village in Chhattisgarh state, which is not in a flood plain, is also arsenic contaminated. More than 170,000 tubewell water samples from the affected states were analyzed and half of the samples had arsenic >10 μg/L (maximum concentration 3,700 μg/L). Chronic exposure to arsenic through drinking water causes various health problems, like dermal, neurological, reproductive and pregnancy effects, cardiovascular effects, diabetes mellitus, diseases of the respiratory and gastrointestinal systems, and cancers, typically involving the skin, lungs, liver, bladder, etc. About 4.5% of the 8,000 children from arsenic-affected villages of affected states were registered with mild to moderate arsenical skin lesions. In the preliminary survey, more than 10,000 patients were registered with different types of arsenic-related signs and symptoms, out of more than 100,000 people screened from affected states. Elevated levels of arsenic were also found in biological samples (urine, hair, nails) of the people living in affected states. The study reveals that the population who had severe arsenical skin lesions may suffer from multiple Bowens/cancers in the long term. Some unusual symptoms, such as burning sensation, skin itching and watering of eyes in the presence of sun light, were also noticed in arsenicosis patients.