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81.
Somnath Dasgupta Jürgen Ehl Michael M. Raith Pulak Sengupta Pranesh Sengupta 《Contributions to Mineralogy and Petrology》1997,129(2-3):182-197
Pelitic rocks were thermally metamorphosed at the contact of the Chimakurthy mafic-ultramafic igneous complex, Eastern Ghats
Belt, India. The rocks show progressive change in mineralogy from biotite-sillimanite-quartz-garnet-K-feldspar (association
I, 150 m from the intrusive contact) to garnet-spinel-cordierite-K-feldspar-sillimanite (association II, 20–30 m from the
intrusive contact) to cordierite-K-feldspar-(cordierite-orthopyroxene-K-feldspar symplectite after osumilite)-spinel-FeTiAl
oxides with/without garnet (associations III and IV, 5 m from the intrusive contact), and finally to spinel-orthopyroxene-cordierite-K-feldspar
(association V, xenoliths). Oxide mineral clots in associations III and IV resemble emery-type rocks. Initial mineral reactions
involved biotite-dehydration melting with partial segregation of the melt. Down-temperature mineral reactions were largely
diffusion controlled and preservation of symplectitic and coronitic textures in microdomains is common. Interpretation of
reaction textures in relevant petrogenetic grids for the sytems KFMASH and FMAS and combined with geothermobarometry suggest
that the pelitic rocks were thermally metamorphosed at c. 6 kbar pressure along a heating-cooling trajectory within the temperature interval between c. 750 °C and c. 1000 °C.
Received: 20 October 1996 / Accepted: 17 June 1997 相似文献
82.
The northern fold belt away from the Singhbhum Shear Zone displays a set of folds on bedding. The folds are sub-horizontal
with E-W to ESE striking steep axial surfaces. In contrast, the folds in the Singhbhum Shear Zone developed on a mylonitic
foliation and have a reclined geometry with northerly trending axes. There is a transitional zone between the two, where the
bedding and the cleavage have become parallel by isoclinal folding and two sets of reclined folds have developed by deforming
the bedding—parallel cleavage. Southward from the northern fold belt the intensity of deformation increases, the folds become
tightened and overturned towards the south while the fold hinges are rotated from the sub-horizontal position to a down-dip
attitude. Recognition of the transitional zone and the identification of the overlapping character of deformation in the shear
zone and the northern belt enable the formulation of a bulk kinematic model for the area as a whole. 相似文献
83.
Mixing behavior in quaternary garnet solid solution and an extended Ellis and Green garnet-clinopyroxene geothermometer 总被引:7,自引:0,他引:7
Pulak Sengupta Somnath Dasgupta P. K. Bhattacharya Y. Hariya 《Contributions to Mineralogy and Petrology》1989,103(2):223-227
Applications of the different formulations of garnet-clinopyroxene geothermometers to crustal granulites and particularly to metamorphosed manganese formations show a wide scatter of estimates. This is primarily related to the uncertainty associated with the formulation of the activity-composition relationship in garnet solid solution besides that in the clinopyroxene solid solution. The largest uncertainty appears to have resulted from the adopted Mg-Mn interaction parameter in garnet which is yet to be experimentally determined. A fresh statistical regression of eleven pairs of garnet and clinopyroxene equilibrated at identical P-T conditions from a manganese formation in India yields W
Mg-Mn
Gt
(=WMn-Mg) value of 1600±500 cal/mols. An extension of the Ellis and Green (1979) geothermometer, known to work well in normal granulites, incorporating terms associated with the activity coefficients of the exchangeable cations, now yields consistent temperature estimation from normal granulites as well as from metamorphosed manganese formations. The geothermometer, however, will not work well for garnet having XFe0.65 and clinopyroxenes containing appreciable Na, Al and/or Fe3+. 相似文献
84.
Stable isotope evidence of dual (Arabian Sea and Bay of Bengal) vapour sources in monsoonal precipitation over north India 总被引:2,自引:0,他引:2
High resolution time series data of hydrogen (δD) and oxygen (δ18O) isotope values of precipitation have been generated for the first time at Kolkata, eastern India where the summer monsoon clouds from Bay of Bengal (BOB) commence their journey over India. Use of a Rayleigh cum two component mixing model and comparison of Kolkata data with the International Atomic Energy Agency (IAEA)–Global Network of Isotopes in Precipitation (GNIP) data base of New Delhi suggest that the precipitation at New Delhi cannot be explained by simple continental effect of a BOB vapour source alone, traveling and raining successively along Kolkata–New Delhi route. It is necessary to invoke an admixture of 20% vapour originating from the Arabian sea with the vapour coming from BOB and finally causing summer monsoon rains at New Delhi. The findings have major implications to the regional water vapour budget over India. 相似文献
85.
Natural Hazards - Landslide susceptibility (LSI) modeling of Darjeeling–Sikkim Himalaya is performed by integrating 28 causative factors on 28C28 combinations on Geographical Information... 相似文献
86.
In this paper, we compare the petrological histories of the Kemp Land Coast (east Antarctica), and Gokavaram area (Eastern Ghats), that were supposed to have been juxtaposed. The area around Gokavaram is dominated by different varieties of paragneisses (pelitic, quartzofeldspathic, and calcareous composition) with relatively minor amounts of orthogneisses (mafic, enderbitic, and granitic composition). The rocks were involved in three major phases of deformation, and were finally affected by localised shear movement. On the basis of reaction textures, well preserved in high Mg-Al granulites, and calc-silicate granulites, and geothermobarometric data we deduce a polymetamorphic evolution of the rocks. Following an early M1 metamorphism culminating at 9.2–9.4 kbar, > 950°C, the rocks cooled nearly isobarically down to 850°C. During a subsequent M2 metamorphism, near isothermal decompression to 5–6 kbar occurred. This was followed by near isobaric cooling down to 600–650°C. M3 is a weak amphibolite facies overprint, largely restricted to late shears, which involved hydration as well. Available radiometric data from this area can be interpreted in terms of partial resetting of U-Pb systematics in older sphenes due to M3 metamorphism at ca. 550 Ma. Despite the absence of sufficient isotopic data on the Eastern Ghats granulites, we document a remarkable similarity in the petrological history of the two supposedly erstwhile neighbours. 相似文献
87.
88.
Torsa Sengupta Arati Deshpande Mukherjee Ravi Bhushan F. Ram M. K. Bera Harsh Raj Ankur J. Dabhi R. S. Bisht Y. S. Rawat S. K. Bhattacharya Navin Juyal Anindya Sarkar 《第四纪科学杂志》2020,35(3):382-395
Radiocarbon dating of archaeological carbonates from seven cultural stages of Dholavira, Great Rann of Kachchh (GRK), the largest excavated Harappan settlement in India, suggests the beginning of occupation at ~5500 years BP (pre-Harappan), and continuation until ~3800 years BP (early part of the Late Harappan period). The settlement rapidly expanded under favourable monsoonal climate conditions when architectural elements such as the Citadel, Bailey, Lower and Middle Town were added between the Early and mid-Mature Harappan periods. Abundant local mangroves grew around the GRK sustaining prolific populations of the edible gastropod Terebralia palustris. Oxygen isotope (δ18O) sclerochronology of Early Harappan gastropod shell suggests seasonal mixing of some depleted (δ18O ~ −12‰) river water in summer/monsoon months (through ancient Saraswati and/or Indus distributary channels) with seawater that periodically inundated the GRK. Evaporation from this semi-enclosed water body during the non-monsoon months enriched the δ18O of water/shell carbonates. The humid fluvial landscape possibly changed due to a catastrophic drought driving the final collapse of the settlement of Dholavira exactly at the onset of the Meghalayan (Late Holocene) stage (~4300–4100 years BP ). Indeed, Dholavira presents a classic case for understanding how climate change can increase future drought risk as predicted by the IPCC working group. Copyright © 2019 John Wiley & Sons, Ltd. 相似文献
89.
Identification and mapping of chromium (VI) plume in groundwater for remediation: A case study at Kanpur,Uttar Pradesh 总被引:1,自引:0,他引:1
R. K. Singh B. Sengupta Rameshwar Bali B. P. Shukla V. V. S. Gurunadharao Rajesh Srivatstava 《Journal of the Geological Society of India》2009,74(1):49-57
With only twenty five percent population living in urban areas, India has cities amongst the biggest in the world. Urban growth
in most of Indian cities is concomitant with rise in water demand for community, as well as, for industrial purposes. The
complex situation resulting from indiscriminate disposal of waste and its severe impact on groundwater quality is set for
continuous worsening mainly for want of sustained effort aimed at site-specific remediation.
The study, a prerequisite for actual remediation in an industrial city of Kanpur, India, envisages detailed investigation
about pollutant transport, evaluation of concept of Bio-remediation and a range of other options and finally full scale implementation
of the best suited. Drilling of piezometers and resistivity survey indicates that the area is constituted of alluvial sands,
gravels and their various admixtures. Chemical analysis of water samples collected from piezometers and hand pumps shows the
presence of hexavalent chromium rich horizons at various depths. The alarming concentration of this carcinogenic heavy metal
of the order of 16.3 mg/l against the permissible concentration (of 0.05 mg/l) for drinking water and high concentration within
sediments of the area poses a major threat to the entire ecosystem. The projection of migration contaminant plume of hexavalent
chromium as depicted in the paper is indicative of a concentrated extent of core zone existing in shallow alluvial aquifer,
which may be targeted for interception by remedial measures.
The present work, elaborating on the source, potential and monitoring the migration of the pollutant plume is the first field
scale study of its kind in the country. The findings of these studies are of strong relevance in addressing the ground water
pollution due to indiscriminate disposal practices of hazardous waste in areas located within the alluvial zones. 相似文献
90.
K. C. Joshi S. Sengupta G. C. Kandpal 《Journal of the Geological Society of India》2010,75(2):383-392
An earthquake of magnitude 5.0 with its epicenter in the West Sikkim district occurred on the evening of 20th May 2007. The macroseismic study revealed an ENE-WSW isoseismal pattern indicating a trend conforming to that of the major
tectonic discontinuities in this part of the Himalaya. 相似文献