Anisotropy of magnetic susceptibility analysis of deformed kaolinite: implications for evaluating landslides     

Manish A. Mamtani  Aniruddha Sengupta 《International Journal of Earth Sciences》2009,98(7):1721-1725

Plane strain tests were performed on seven kaolinite blocks, each of which developed shear bands. Anisotropy of magnetic susceptibility (AMS) analysis of the kaolinite reveals a threshold degree of magnetic anisotropy (P′) exceeding which shear bands develop. Since P′ is a strain-intensity gauge and soils are known to develop shear bands prior to landsliding, it is concluded that soil in every landslide-prone region must have its unique threshold P′ exceeding which it develops shear bands before failing. Therefore, AMS monitoring of soil in landslide prone regions is proposed as a potential tool in the management of natural hazard zones.  相似文献   

Dynamic Behavior of Small Scale Nailed Soil Slopes     

Debabrata Giri  Aniruddha Sengupta 《Geotechnical and Geological Engineering》2009,27(6):687-698

The shaking table tests are conducted on small scale nailed embankment slopes to study their behavior under dynamic conditions. Medium grained local sand with a water content of 3% is used in the study. The embankment slope is constructed using the controlled-volume compaction method. Three slope angles, 30°, 35° and 40° with a constant slope height of 18 cm are considered for the embankment. Each slope is reinforced with six number of hollow aluminum nails in two rows. The ratio of the length of nail to slope height (0.82) is same for all model slopes. The nails are inserted at three different inclinations. Three strain gauges are glued to each nail to obtain local strains during shaking. The accelerations at the base and the crest of the model slopes are monitored to find the acceleration responses of the embankments during the input ground motions. The numerical simulation of the model tests is performed by a commercial program called FLAC. The results of the numerical analyses are found to be reasonably close to the corresponding experimental results.  相似文献   

Fractal analysis of major faults in India on a regional scale     

P. Sengupta  S. K. Nath  K. K. S. Thingbaijam  S. Mistri 《Journal of the Geological Society of India》2011,78(3):226-232

The seismicity of a region is implicit of the causal faulting mechanisms and geodynamic diversity of the subsurface regime nucleating earthquakes of different magnitudes, several of which may be as devastating as ones historically reported in global perspective of tectonic complexity as in the case of India. Fractal analysis using box-counting method for the major fault networks across the country estimates fractal dimension, D_f, values to be varying between 0.88 and 1.36. The fault segments in parts of northwest Himalayas, northeast India and Indo-Gangetic plains, are observed to be associated with higher D_f values implicating high seismicity rates. On the other hand, low D_f values in the peninsular India indicate isolated pattern of the underlying faults. The fractal dimension is observed to be indicative of predominant faulting types — higher values conforming to thrust faulting mechanism while lower to strike slip tectonism.  相似文献   

Significance of mineral chemistry of syenites and associated rocks of Elagiri complex,Southern Granulite Terrane of the Indian shield     

Sarmistha Mukhopadhyay  Jyotisankar Ray  Basab Chattopadhyay  Shyamal Sengupta  Biswajit Ghosh  Subrata Mukhopadhyay 《Journal of the Geological Society of India》2011,77(2):113-129

The Elagiri complex (12°31′ N: 78°35′ E) represents one of the important silica — oversaturated syenite plutons of the Southern Granulite Terrane of the Indian shield. This article for the first time reports the mineral chemistry of the Elagiri complex and brings out important petrogenetic significance. The litho-members of Elagiri complex are intrusive into high grade country rocks viz. granite gneiss, amphibolite and pyroxene granulite. The country rocks are foliated bearing evidences of multiple folding and deformation. On the other hand, the constituent litho members of the Elagiri complex (syenites, gabbro and later intrusives marked by lamprophyre and carbonatite) show preservation of igneous layering in terms of discernible parallelism of the constituent minerals. The Elagiri complex shows presence of sharp contacts among litho members and marked absence of chilled facies peripheral to the margin. Electron microprobe data have been critically used to systematize the constituent mineral-phases of the different lithomembers of the complex. Geothermobarometric data indicate a temperature of equilibration in the range of ∼700° to 500°C at ∼2.0 to 5.2 kb which corresponds to shallow level (cf. 18.2 km) equilibration-depth of the complex. Field observations and mineral chemistry data suggest that liquid immiscibility plays an important role during the evolution of the Elagiri complex.  相似文献   

Petrology of the mafic sill of Narshingpur-Lakhnadon section,Eastern Deccan volcanic province     

Piyali Sengupta  Jyotisankar Ray 《Journal of the Geological Society of India》2011,77(4):309-327

Deccan volcanism with a tremendous burst of volcanic activity marks a unique episode in Indian geological history and covers nearly two third of Peninsular India. Occurrences of mafic sill in the continental basalts are rather rare throughout the flood basalt provinces and only few sporadic reports have been described from different Continental Flood Basalts of the world. In the present article, petrology of mafic sill from the Narshingpur-Lakhnadon section of Eastern Deccan province of India has been presented. The mafic sill in the field is found to occur in a relatively deep valley amidst Gondwana rocks, which occur as the basement of the extrusion. The sill is spatially associated with three initial flows viz. flow I, II and III of adjacent Narshingpur-Harrai-Amarwara section. The sill in its central part is a medium grained rock and petrographically corresponds to dolerite containing augite, plagioclase and rare olivine grains; the chilled facies of the sill is characterized by phenocrysts of olivine, plagioclase and augite that are set in groundmass consisting predominantly of plagioclase, olivine and glass. Mineral chemistry indicates that olivine phenocrystal phase is magnesian (Fo61). Plagioclase phenocrystal composition ranges from An 51 to An 71 whereas the same variation of the groundmass plagioclase composition corresponds to An 31 to An 62. The overlap in the compositions for groundmass and phenocrystal plagioclase may be explained due to fluctuating PH2O condition. The pyroxene compositions (both groundmass and phenocryst) in majority of the cases are clubbed well within the augite field, however, in a few cases, groundmass compositions are found to fall in the sub-calcic augite and pigeonite field. Some zoned pyroxene phenocrysts, characteristically display different types of zoning patterns. Opaque minerals in the mafic sill are found to be magnetite and ilmenite and this coexisting iron-oxide composition helps to constrain the prevalent fO2 condition in the parent magma. The geochemistry of the mafic sill and associated basaltic lava flows indicates close genetic link amongst them. Critical consideration of trace elements indicates a distinct enriched mantle source (EM-I/EM-II/HIMU) for the parental magma. Trace element modeling indicates that equilibrium batch-melting of plume source followed by fractionation of olivine, clinopyroxene and plagioclase and subsequent heterogeneous mixing of melt and settled crystals can very well explain the genesis of the mafic sill and the associated basaltic flows.  相似文献   

Crossover of cation partitioning in olivines: a combination of ab initio and Monte Carlo study     

Swastika Chatterjee  Sirshendu Bhattacharyya  Surajit Sengupta  Tanusri Saha-Dasgupta 《Physics and Chemistry of Minerals》2011,38(4):259-265

We report studies based on a combination of ab initio electronic structure and Monte Carlo (MC) technique on the problem of cation partitioning among inequivalent octahedral sites, M1 and M2 in mixed olivines containing Mg²⁺ and Fe²⁺ ions. Our MC scheme uses interactions derived out of ab initio, density functional calculations carried out on measured crystal structure data. Our results show that there is no reversal of the preference of Fe for M1 over M2 as a function of temperature. Our findings do not agree with the experimental findings of Redfern et al. (Phys Chem Miner 27:630–637, 2000), but are in agreement with those of Heinemann et al. (Eur J Mineral 18:673–689, 2006) and Morozov et al. (Eur J Mineral 17:495–500, 2005).  相似文献   

Patterns of foliation drag near walls of reoriented dykes     

Sudipta Sengupta 《Journal of Earth System Science》1995,104(3):433-446

Drag patterns of foliation are graphically constructed around very competent dykes under bulk strain of pure shear, simple shear and a combination of pure shear and simple shear. Four different types of drag patterns may be produced, depending on the nature of the bulk deformation and the initial orientations of the dyke and the foliation. The drag pattern can be symmetric or asymmetric, inward curving or outward curving. Both the magnitude and the sense of drag may vary along a dyke wall. A uniform sense of drag develops all along a dyke wall only in certain special situations. The type of foliation drag near a dyke may give us a rough idea of the nature of bulk deformation and the relative orientations of the dyke and the foliation with respect to the bulk strain axes.  相似文献   

Tectonics of the ophiolite belt from Naga Hills and Andaman Islands,India   总被引：1，自引：0，他引：1  

S. K. Acharyya  K. K. Ray  S. Sengupta 《Journal of Earth System Science》1990,99(2):187-199

The ophiolitic rocks of Naga Hills-Andaman belt occur as rootless slices, gently dipping over the Paleogene flyschoid sediments, the presence of blue-schists in ophiolite melange indicates an involvement of the subduction process. Subduction was initiated prior to mid-Eocene as proved by the contemporaneous lower age limit of ophiolite-derived cover sediment as against the accreted ophiolites and olistostromal trench sediment. During the late Oligocene terminal collision between the Indian and Sino-Burmese blocks, basement slivers from the Sino-Burmese block, accreted ophiolites and trench sediments from the subduction zone were thrust westward as nappe and emplaced over the down-going Indian plate. The geometry of the ophiolites and the presence of a narrow negative gravity anomaly flanking their map extent, run counter to the conventional view that the Naga-Andaman belt marks the location of the suture. The root-zone of the ophiolite nappe representing the suture is marked by a partially-exposed eastern ophiolite belt of the same age and gravity-high zone, passing through central Burma-Sumatra-Java. The ophiolites of the Andaman and Naga Hills are also conventionally linked with the subduction activity, west of Andaman islands. This activity began only in late Miocene, much later than onland emplacement of the ophiolites; it further developed west of the suture in its southern part. Post-collisional northward movement of the Indian plate subparallel to the suture, also developed leaky dextral transcurrent faults close to the suture and caused Neogene-Quatemary volcanism in central Burma and elsewhere.  相似文献   

Groundwater arsenic contamination in Ganga–Meghna–Brahmaputra plain, its health effects and an approach for mitigation     

Dipankar Chakraborti  Mohammad Mahmudur Rahman  Bhaskar Das  Bishwajit Nayak  Arup Pal  Mrinal Kumar Sengupta  Md. Amir Hossain  Sad Ahamed  Manabendranath Sahu  Kshitish Chandra Saha  Subhash Chandra Mukherjee  Shyamapada Pati  Rathindra Nath Dutta  Quazi Quamruzzaman 《Environmental Earth Sciences》2013,70(5):1993-2008

The authors’ survey of the Ganga–Meghna–Brahmaputra (GMB) plain (area 569,749 km²; population >500 million) over the past 20 years and analysis of more than 220,000 hand tube-well water samples revealed groundwater arsenic contamination in the floodplains of the Ganga–Brahmaputra river (Uttar Pradesh, Bihar, Jharkhand, West Bengal, and Assam) in India and the Padma–Meghna–Brahmaputra river in Bangladesh. On average, 50 % of the water samples contain arsenic above the World Health Organization guideline value of 10 μg/L in India and Bangladesh. More than 100 million people in the GMB plain are potentially at risk. The authors’ medical team screened around 155,000 people from the affected villages and registered 16,000 patients with different types of arsenical skin lesions. Arsenic neuropathy and adverse pregnancy outcomes have been recorded. Infants and children drinking arsenic-contaminated water are believed to be at high risk. About 45,000 biological samples analyzed from arsenic-affected villages of the GMB plain revealed an elevated level of arsenic present in patients as well as non-patients, indicating that many are sub-clinically affected. In West Bengal and Bangladesh, there are huge surface water in rivers, wetlands, and flooded river basins. In the arsenic-affected GMB plain, the crisis is not over water scarcity but about managing the available water resources.  相似文献   

The Lambert <Emphasis Type="Italic">W</Emphasis> function and solutions to Kepler’s equation     

Prasenjit Sengupta 《Celestial Mechanics and Dynamical Astronomy》2007,99(1):13-22

This paper presents a method for the truncation of infinite Fourier–Bessel representations for functions requiring a solution to Kepler’s equation. Use is made of the Lambert W function to solve for the desired index that bounds the remainder terms of the series, within the prescribed tolerance. The enforcement of a maximum on the number of Bessel functions is also useful in truncating the Bessel functions themselves, resulting in an analytical representation of the solution to a desired tolerance, without the use of infinite series.  相似文献