Evolution of Mayurbhanj Granite Pluton, eastern Singhbhum, India: a case study of petrogenesis of an A-type granite in bimodal association     

Saumitra Misra  Subha Sankar Sarkar  Sambhunath Ghosh 《Journal of Asian Earth Sciences》2002,20(8)

The A-type Mayurbhanj Granite Pluton (3.09 Ga), occurring along the eastern margin of the Singhbhum-Orissa Craton, eastern India, represents the final phase of acid plutonism in this crustal block of Archean age. The granite shows a bimodal association with a voluminous gabbroid body, exposed mainly along its western margin, and is associated with the Singhbhum Shear zone. The granite pluton is composed mainly of a coarse ferrohastingsite–biotite granite phase, with an early fine-grained granophyric microgranitic phase and a late biotite aplogranitic phase. Petrogenetic models of partial melting, fractional crystallisation and magma mixing have been advocated for the evolution of this pluton. New data, combined with earlier information, suggest that two igneous processes were responsible for the evolution of the Mayurbhanj Granite Pluton: partial melting of the Singhbhum Granite; followed by limited amount of mixing of acid and basic magmas in an anorogenic extensional setting. The necessary heat for partial melting was provided by the voluminous basaltic magma, now represented by the gabbroid body, emplaced at a shallow crustal level and showing a bimodal association with the Mayurbhanj Granite Pluton. The Singhbhum Shear Zone provided a possible channel way for the emplacement of the basic magma during crustal extension. It is concluded that all three phases of the Mayurbhanj Granite Pluton were derived from the same parent magma, generated by batch partial melting of the Singhbhum Granite at relatively high temperatures (980 °C) and low pressures (4 to <2 kbar) under anhydrous conditions. The coarse ferrohastingsite biotite granite phase shows evidence of limited and heterogeneous assimilation of country rock metasediments. However, the early microgranite phase and late aplogranite phase have not assimilated any metasediments. Compositional irregularities observed along the western margin of the Mayurbhanj Granite Pluton in contact with the gabbro body including a continuous fractionating sequence from quartz diorite to alkali-feldspar granite in the Notopahar area. Gradational contacts between the gabbro and the Mayurbhanj Granite Pluton in the Gorumahisani area etc., may be attributed to a limited amount of mixing between the gabbroid magma and the newly generated Mayurbhanj Granite magma. The mixing was mainly of liquid–liquid diffusive type, with a subordinate amount of mixing of solid–liquid type. Although A-type granites are commonly described as having high total REE (e.g. 270–400 ppm), studies on the late aplogranite phase of the Mayurbhanj Granite show that total REE values (100 ppm) are low. This low REE abundance may be attributed to the progressive residual nature of the Singhbhum Granite source during continued partial melting, when the magmas of the microgranite and coarse granite phases had already been removed from the source region.  相似文献   

Modulation of ionospheric conductivities during high-power wave propagation     

S. S. De  B. K. Sarkar  B. Ghosh  A. C. Sen  S. Bandyopadhyay  S. K. Adhikari 《Earth, Moon, and Planets》1991,53(1):1-10

Enhancement of conductivity tensor modification within the ionospheric plasma by electron density modulation through the temperature dependence of the recombination rates of different ionspecies caused due to electron temperature modulation during high-power wave propagation is studied. Variation of Hall and Pedersen conductivities of the ionosphere has been investigated in the height range between 85 km to 250 km. The generation of waves at the modulation frequency and its harmonics in the ELF, VLF bands in the process is discussed.  相似文献   

Simulating Solar Cycles in Northern and Southern Hemispheres by Assimilating Magnetic Data into a Calibrated Flux-Transport Dynamo     

Mausumi Dikpati  Peter A. Gilman  Giuliana de Toma  Siddhartha S. Ghosh 《Solar physics》2007,245(1):1-17

We use the flux-transport dynamo prediction scheme introduced by Dikpati, de Toma, and Gilman (Geophys. Res. Lett. 33, L05102, 2006) to make separate simulations and predictions of sunspot cycle peaks for northern and southern hemispheres. Despite the division of the data, the skill level achieved is only slightly lower than that achieved for the sum of both hemispheres. The model shows skill at simulating and predicting the difference in peaks between North and South, provided that difference is more than a few percent. The simulation and prediction skill is achieved without adjustment to any parameters of the model that were used when peaks for the sum of North and South sunspot areas was simulated. The results are also very insensitive to the averaging length applied to the input data, provided the simulations and predictions are for peaks defined by averaging the observations over at least 13 rotations. However, in its present form, the model is not capable of skillfully simulating or predicting short-time-scale features of individual solar cycles.  相似文献   

Geochemistry of some banded iron-formations of the Archean supracrustals,Jharkhand-Orissa region,India     

H. N. Bhattacharya  Indranil Chakraborty  Kaushik K. Ghosh 《Journal of Earth System Science》2007,116(3):245-259

Banded iron-formations (BIF) form an important part of the Archean supracrustal belts of the Jharkhand-Orissa region, India. Major, trace and REE chemistry of the banded iron-formation of the Gandhamardan, Deo Nala, Gorumahisani and Noamundi sections of the Jharkhand-Orissa region are utilized to explore the source of metals and to address the thermal regime of the basin floor and the redox conditions of the archean sea. Hydrothermal fluids of variable temperatures might have contributed the major part of the Fe and other trace elements to the studied banded iron-formations. Diagenetic fluids from the sea floor sediments and river water might have played a subdued role in supplying the Fe and other elements for the banded iron-formations.  相似文献   

Remote sensing based sedimentation study of maithon reservoir     

Pankaj Mani  Biswajit Chakravorty 《Journal of the Indian Society of Remote Sensing》2007,35(1):117-120

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Hydro-geochemical controls on removal of Cr(VI) from contaminated groundwater by anion exchange     

Biswajit Mukhopadhyay  Jon Sundquist  Eric White 《Applied Geochemistry》2007

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Probes of cosmic star formation history     

Pranab Ghosh 《Journal of Astrophysics and Astronomy》2002,23(1-2):107-113

I summarize X-ray diagnostic studies of cosmic star formation history in terms of evolutionary schemes for X-ray binary evolution in normal galaxies with evolving star formation. Deep X-ray imaging studies byChandra andXMM-Newton are now beginning to constrain both the X-ray luminosity evolution of galaxies and the logN- logS diagnostics of the X-ray background. I discuss these in the above context, summarizing current understanding and future prospects.  相似文献   

C-O bonds in carbonate minerals: A new kind of paleothermometer     

Prosenjit Ghosh  Jess Adkins  Brian Balta  Edwin A. Schauble  John M. Eiler 《Geochimica et cosmochimica acta》2006,70(6):1439-1456

The abundance of the doubly substituted CO₂ isotopologue, ¹³C¹⁸O¹⁶O, in CO₂ produced by phosphoric acid digestion of synthetic, inorganic calcite and natural, biogenic aragonite is proportional to the concentration of ¹³C-¹⁸O bonds in reactant carbonate, and the concentration of these bonds is a function of the temperature of carbonate growth. This proportionality can be described between 1 and 50 °C by the function: Δ₄₇ = 0.0592 · 10⁶ · T⁻² − 0.02, where Δ₄₇ is the enrichment, in per mil, of ¹³C¹⁸O¹⁶O in CO₂ relative to the amount expected for a stochastic (random) distribution of isotopes among all CO₂ isotopologues, and T is the temperature in Kelvin. This relationship can be used for a new kind of carbonate paleothermometry, where the temperature-dependent property of interest is the state of ordering of ¹³C and ¹⁸O in the carbonate lattice (i.e., bound together vs. separated into different CO₃²⁻ units), and not the bulk δ¹⁸O or δ¹³C values. Current analytical methods limit precision of this thermometer to ca. ± 2 °C, 1σ. A key feature of this thermometer is that it is thermodynamically based, like the traditional carbonate-water paleothermometer, and so is suitable for interpolation and even modest extrapolation, yet is rigorously independent of the δ¹⁸O of water and δ¹³C of DIC from which carbonate grew. Thus, this technique can be applied to parts of the geological record where the stable isotope compositions of waters are unknown. Moreover, simultaneous determinations of Δ₄₇ and δ¹⁸O for carbonates will constrain the δ¹⁸O of water from which they grew.  相似文献   

Combined effects of water pH and alkalinity on the accumulation of lead, cadmium and chromium to Labeo rohita (Hamilton)     

S. Adhikari Ph.D.  L. Ghosh Ph.D.  S. Ayyappan Ph.D. 《International Journal of Environmental Science and Technology》2006,3(3):289-296

Influence of pH (5.5, 7.0 and 8.5) and alkalinity (40 to 200 mg/L as CaCO₃) on the accumulation of Pb (NO₃)₂ CdCl₂, H₂O and K₂Cr₂O₇ to Labeo rohita (Hamilton) was investigated in the laboratory. Highest accumulation of Pb and Cr in whole fish occurred at pH 5.5 and at alkalinity level of 40 to 46 mg/L as CaCO₃ compared to 7.0 and 8.5. In case of Cd maximum accumulation occurred at pH 7.0 and at alkalinity of 100 mg/L as CaCO₃ than that of pH 5.5 and 8.5 and alkalinity 42 and 156 mg/L as CaCO₃. Maximum accumulation of lead and chromium occurred at total alkalinity level of 40 and 46 mg/L as CaCO₃, respectively while maximum accumulation of cadmium occurred at an alkalinity level of 200 mg/L as CaCO₃. A significant (p<0.05) linear relationship was demonstrated between increasing pH/ alkalinity and decreasing accumulation in Pb and Cr treatment at all exposure period while for Cd there was no significant linear relationship established.  相似文献   

Far-infrared brightness temperature of Saturn's disk and rings     

R.R. Daniel  S.K. Ghosh  K.V.K. Iyengar  T.N. Rengarajan  S.N. Tandon  R.P. Verma 《Icarus》1982,49(2):205-212

We present far-infrared observations of Saturn in the wavelength band 76–116 μm, using a balloon-borne 75-cm telescope launched on 10 December 1980 from Hyderabad, India, when B′, the Saturnicentric latitude of the Sun, was 4°.3. Normalizing with respect to Jupiter, we find the average brightness temperature of the disk-ring system to be 90 ± 3° K. Correcting for the contribution from rings using experimental information on the brightness temperature of rings at 20 μm, we find T_D, the brightness temperature of the disk, to be 96.9 ± 3.5° K. The systematic errors and the correction for the ring contribution are small for our observations. We, therefore, make use of our estimate of T_D and earlier observations of Saturn when contribution from the rings was large and find that for wavelengths greater than 50 μm, there is a small reduction in the ring brightness temperature as compared to that at 20 μm.  相似文献