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41.
Ria Mukherjee Sisir K. Mondal Minik T. Rosing Robert Frei 《Contributions to Mineralogy and Petrology》2010,160(6):865-885
The chromite deposits in the Archean Nuggihalli schist belt are part of a layered ultramafic–mafic sequence within the Western
Dharwar Craton of the Indian shield. The 3.1-Ga ultramafic–mafic units occur as sill-like intrusions within the volcano-sedimentary
sequences of the Nuggihalli greenstone belt that are surrounded by the tonalite–trondhjemite–granodiorite (TTG) suite of rocks.
The entire succession is exposed in the Tagdur mining district. The succession has been divided into the lower and the upper
ultramafic units, separated by a middle gabbro unit. The ultramafic units comprise of deformed massive chromitite bodies that
are hosted within chromite-bearing serpentinites. The chromitite bodies occur in the form of pods and elongated lenses (~60–500 m
by ~15 m). Detailed electron microprobe studies reveal intense compositional variability of the chromite grains in silicate-rich
chromitite (~50% modal chromite) and serpentinite (~2% modal chromite) throughout the entire ultramafic sequence. However,
the primary composition of chromite is preserved in the massive chromitites (~60–75% modal chromite) from the Byrapur and
the Bhaktarhalli mining district of the Nuggihalli schist belt. These are characterized by high Cr-ratios (Cr/(Cr + Al) = 0.78–0.86)
and moderate Mg-ratios (Mg/(Mg + Fe2+) = 0.38–0.58). The compositional variability occurs due to sub-solidus re-equilibration in the accessory chromite in the
serpentinite (Mg-ratio = 0.01–0.38; Cr-ratio = 0.02–0.99) and in silicate-rich chromitite (Mg-ratio = 0.06–0.48; Cr-ratio = 0.60–0.99).
In the massive chromitites, the sub-solidus re-equilibration for chromite is less or absent. However, the re-equilibration
is prominent in the co-existing interstitial and included olivine (Fo96–98) and pyroxene grains (Mg-numbers = 97–99). Compositional variability on the scale of a single chromite grain occurs in the
form of zoning, and it is common in the accessory chromite grains in serpentinite and in the altered grains in chromitite.
In the zoned grains, the composition of the core is modified and the rim is ferritchromit. In general, ferritchromit occurs
as irregular patches along the grain boundaries and fractures of the zoned grains. In this case, ferritchromit formation is
not very extensive. This indicates a secondary low temperature hydrothermal origin of ferritchromit during serpentinization.
In some occurrences, the ferritchromit rim is very well developed, and only a small relict core appears to remain in the chromite
grain. However, complete alteration of the chromite grains to ferritchromit without any remnant core is also present. The
regular, well-developed and continuous occurrence of ferritchromit rims around the chromite grain boundaries, the complete
alteration of the chromite grains and the modification of the core composition indicate the alteration in the Nuggihalli schist
belt to be intense, pervasive and affected by later low-grade metamorphism. The primary composition of chromite has been used
to compute the nature of the parental melt. The parental melt calculations indicate derivation from a high-Mg komatiitic basalt
that is similar to the composition of the komatiitic rocks reported from the greenstone sequences of the Western Dharwar Craton.
Tectonic discrimination diagrams using the primary composition of chromites indicate a supra-subduction zone setting (SSZ)
for the Archean chromitites of Nuggihalli and derivation from a boninitic magma. The composition of the komatiitic basalts
resembles those of boninites that occur in subduction zones and back-arc rift settings. Formation of the massive chromitites
in Nuggihalli may be due to magma mixing process involving hydrous high-Mg magmas or may be related to intrusions of chromite
crystal laden magma; however, there is little scope to test these models because the host rocks are highly altered, serpentinized
and deformed. The present configurations of the chromitite bodies are related to the multistage deformation processes that
are common in Archean greenstone belts. 相似文献
42.
The overexploitation of groundwater in some parts of the country induces water quality degradation. The untreated industrial effluents discharged on the surface causes severe groundwater pollution in the industrial belt of the country. This poses a problem of supply of hazard free drinking water in the rural parts of the country. There are about 80 tanneries operating in and around Dindigul town in upper Kodaganar river basin, Tamilnadu, India. The untreated effluents from the tanneries have considerably affected the quality of groundwater in this area. To assess the extent of groundwater deterioration, a detailed analysis of groundwater quality data has been carried out. The concentration of cations such as Calcium (Ca2+), Magnesium (Mg2+), Sodium (Na+) and Potassium (K+), and anions such as Bicarbonate (HCO3–), Sulphate (SO42–), Chloride (Cl–) and Nitrate (NO3–) in the groundwater have been studied. Apart from these constituents, pH, electrical conductivity (EC), total dissolved solid and total hardness (TH as CaCO3) were also studied. The correlation of these constituents with the EC has been carried out. The highest correlation is observed between EC and chloride with a correlation coefficient of 0.99. Progressive reduction in correlation coefficients for Mg2+, (Na+ + K+), Ca2+ and SO42– are observed as 0.91, 0.87, 0.86 and 0.56, respectively. It is found that the quality of groundwater in the area under investigation is deteriorated mainly due to extensive use of salt in the leather industries. 相似文献
43.
Abhay Kumar Singh G. C. Mondal P. K. Singh S. Singh T. B. Singh B. K. Tewary 《Environmental Geology》2005,48(8):1014-1028
Water samples collected from the six reservoirs of Damodar River basin in pre- and post-monsoon, have been analysed, to study
the major ion chemistry and the weathering and geochemical processes controlling the water composition. Ca, Na and HCO3 dominate the chemical composition of the reservoir water. The seasonal data shows a minimum concentration of most of the
ions in post-monsoon and a maximum concentration in pre-monsoon seasons, reflecting the concentrating effects due to elevated
temperature and increased evaporation during the low water level period of the pre-monsoon season. Water chemistry of the
reservoirs strongly reflects the dominance of continental weathering aided by atmospheric and anthropogenic activities in
the catchment area. Higher concentration of SO4 and TDS in Panchet, Durgapur and Tenughat reservoirs indicate mining and anthropogenic impact on water quality. The high
contribution of (Ca+Mg) to the total cations, high concentration of dissolved silica, relatively high (Na+K)/TZ+ ratio (0.3) and low equivalent ratio of (Ca+Mg)/(Na+K) suggests combined influence of carbonate and silicate weathering.
Kaolinite is the possible mineral that is in equilibrium with the water, implying that the chemistry of reservoir water favours
kaolinite formation. The calculated values of SAR, RSC and sodium percentage indicate the ‘excellent to good quality’ of water
for irrigation uses. 相似文献
44.
The rare earth element patterns of the gneisses of Bastar and Bundelkhand are marked by LREE enrichment and HREE depletion
with or without Eu anomaly. The spidergram patterns for the gneisses are characterized by marked enrichment in LILE with negative
anomalies for Ba, P and Ti. The geochemical characteristics exhibited by the gneisses are generally interpreted as melts generated
by partial melting of a subducting slab. The style of subduction was flat subduction, which was most common in the Archean.
The rare earth patterns and the multi-element diagrams with marked enrichment in LILE and negative anomalies for Ba, P and
Ti of the granitoids of both the cratons indicate interaction between slab derived melts and the mantle wedge. The subduction
angle was high in the Proterozoic. Considering the age of emplacement of the gneisses and granitoids that differs by ∼ 1 Ga,
it can be assumed that these are linked to two independent subduction events: one during Archaean (flat subduction) that generated
the precursor melts for the gneisses and the other during the Proterozoic (high angle subduction) that produced the melts
for the granitoids. The high values of Mg #, Ni, Cr, Sr and low values of SiO2 in the granitoids of Bastar and Bundelkhand cratons compared to the gneisses of both the cratons indicate melt-mantle interaction
in the generation of the granitoids. The low values of Mg#, Ni, Cr, Sr and high values of SiO2 in the gneisses in turn overrules such melt-mantle interaction. 相似文献
45.
Sisir K. Mondal 《Journal of the Geological Society of India》2011,78(4):390-391
News and Notes
National Seminar on Orissa’s Mineral, Environment and Geosciences Assessment — 2011 (OMEGA-2011) and Golden Jubilee of Geological Survey of India, Orissa — M. Mohanty and K. C. Sahoo (Email: manoranjanmoha@gmail.com) 相似文献46.
47.
48.
Saurodeep Chatterjee Supriya Mondal Debesh Gain Tapan Kr Baidya Dipanjan Mazumdar 《Journal of Earth System Science》2018,127(6):89
The present work deals with the generations of Fe–Ti oxides and the variation in magnetic fabrics of the Dalma lavas and associated meta-sediments of the Singhbhum Mobile Belt (SMB) in relation to tectonics. Generations of the Fe–Ti oxides are different in meta-sediments and volcanics, the former preserving upliftment related oxidised grains, whereas the latter contains fresh grains prompting towards their upliftment due to plume upwelling before the volcanic eruption. In the meta-sediments, the magnetic fabric has close accordance with \(\hbox {D}_{2}/\hbox {F}_{2}\) event revealing synchronous development with \(\hbox {D}_{2}\). The Dalma thrust developed a sudden break in the homogeneity of the magnetic fabrics of the rocks where the magnetic foliations are all parallel to the Dalma thrust. This also causes \(P_{j}\) to be highest in this sector. The magnetic fabrics of volcanic rocks are different from the meta-sediments and record no signature of deformation. The pattern of distribution of susceptibility axes are in accordance with the subaerial lava flows. However, their \(\hbox {K}_{1}\) and \(\hbox {K}_{2}\) dispersed throughout the periphery with \(\hbox {K}_{3}\) clustering at the centre. This infers towards the fact that although the volcanism took place in a subaerial environment, calm aqueous environment was locally present where the oblate grains settled on the eruption surface with their \(\hbox {K}_{3}\) vertical. 相似文献
49.
North-eastern Himalaya is said to be one of the world most complex geological set-up with different kinds of seismotectonic systems. Region has experienced two of the world’s strongest earthquakes, such as Shillong earthquake of 1897 known as Assam earthquake and subsequent 1950 earthquake in Arunachal Pradesh, both of with magnitude of 8.7, and also several other strong earthquakes. Various techniques have been applied to understand the past strong earthquake mechanism as well as hazard estimation carried out for future earthquake. Fractal correlation dimension (D c) is being used in this study with the seismicity for the period 1961 to recent for understanding the pattern of seismic hazard. The entire area has been divided into four major tectonic blocks, and each block event was divided into consecutive fifty events window for seeing spatiotemporal patterns. After comparing the patterns, we have identified that Block of Eastern Himalaya near Main Central Thrust, Main Boundary Thrust, north of Kopili lineament and Block of Shillong plateau near Dauki fault are having relatively intense clustering of events in recent times, which may be identified as the zones of most potential to have a strong event. 相似文献
50.
B. Das N. K. Mondal R. Bhaumik P. Roy 《International Journal of Environmental Science and Technology》2014,11(4):1101-1114
In the present study, adsorption of lead (II) ions from aqueous solution by alluvial soil of Bhagirathi River was investigated under batch mode. The influence of solution pH, sorbent dose, initial lead (II) concentration, contact time, stirring rate and temperature on the removal process were investigated. The lead adsorption was favored with maximum adsorption at pH 6.0. Sorption equilibrium time was observed in 60 min. The equilibrium adsorption data were analyzed by the Freundlich, Langmuir, Dubinin–Radushkevich and Temkin adsorption isotherm models. The kinetics of lead (II) ion was discussed by pseudo first-order, pseudo second-order, intra-particle diffusion, and surface mass transfer models. It was shown that the adsorption of lead ions could be described by the pseudo second-order kinetic model. The activation energy of the adsorption process (E a) was found to be ?38.33 kJ mol?1 using the Arrhenius equation, indicating exothermic nature of lead adsorption onto alluvial soil. Thermodynamic parameters, such as Gibbs free energy (?G 0), the enthalpy (?H 0), and the entropy change of sorption (?S 0) have also been evaluated and it has been found that the adsorption process was spontaneous, feasible, and exothermic in nature. The results indicated that alluvial soil of Bhagirathi River can be used as an effective and low cost adsorbent to remove lead ions from aqueous solutions. 相似文献