Cation diffusion in aluminosilicate garnets: experimental determination in spessartine-almandine diffusion couples,evaluation of effective binary diffusion coefficients,and applications   总被引：9，自引：1，他引：8  

Sumit Chakraborty  Jibamitra Ganguly 《Contributions to Mineralogy and Petrology》1992,111(1):74-86

We present new experimental data on diffusion of divalent cations in almandine-spessartine diffusion couples in graphite capsules in the P-T range of 14–35 kb, 1100–1200° C. The tracer diffusion coefficients of the major divalent cations, viz. Fe, Mg and Mn, retrieved from the multicomponent diffusion profiles, have been combined with earlier data from our laboratory at 29–43 kb, 1300–1480° C (Loomis et al. 1985) to derive expressions of the P-T dependence of the diffusion coefficients at fO₂ approximately corresponding to that defined by equilibrium in the system graphite-O₂. We review the conditions, discussed earlier by Cooper, under which the flux of a component in a multicomponent system becomes proportional to its concentration gradient (Fickian diffusion), as if the entire solvent matrix behaves as a single component, and also suggest a method of incorporating the thermodynamic effect on diffusion in the same spirit. Regardless of the magnitude or sign of the off-diagonal terms of the D matrix, it is always possible to define an effective binary diffusion coefficient (EBDC) of a component in a semi-infinite multicomponent diffusion-couple experiment such that it has the property of the Fickian diffusion coefficient, provided that there is no inflection on the diffusion profiles. It is shown that the success of Elphick et al. in fitting the experimental diffusion profiles of all components over a limited concentration range by a single diffusion coefficient is due to fortuitous similarity of the EBDCs of the components (Fe, Mg, Mn and Ca) in their diffusion couple experiments. In common metapelitic garnets showing compositional zoning, the EBDCs of the divalent cations do not differ from each other by more than a factor of 2.5. However, the EBDC of a component changes from core to rim by a factor of 3 to 12, depending on the composition. We suggest a method of volume averaging of the EBDC which should prove useful in approximate calculations of diffusion flux during relaxation of compositional zoning. The EBDC of Mn is found to reduce essentially to D _MnMn, the main diagonal term of the D matrix, and consequently can be calculated quite easily. Evaluation of EBDC of Fe, Mg and Mn in garnets from a prograde Barrovian sequence did not reveal any significant dependence on the extent of relaxation of garnet. The diffusion data have been applied to calculate the cooling rate of natural biotite-garnet diffusion couple from eastern Finland and diffusional modification of growth zoning in garnet in early Proterozoic Wopmay orogen, Canada. The results are in good agreement with geochronological and other independent constraints.Symbols and abbreviations a Radius of a spherical garnet crystal - BSE Back-scattered electron imaging - C Column vector of (n-1) independent components - D Diffusion coefficient matrix - D _ij An element of the diffusion matrix on the i th row and j th column - D _* ⁱ Tracer diffusion coefficient of component i - D(i) Effective interdiffusion coefficient (EIC) of various components in a multicomponent solution rich in the component i - D(i-j) Interdiffusion coefficient of components i and j in a binary solution - D _i (EB) Effective binary diffusion coefficient of component i in a multicomponent solution - D _i (EB:Ideal) D _i (EB) under condition of ideal thermodynamic mixing of the diffusing species - D _i (EB:thermo) Thermodynamic component of D _i(EB) - D _O ^A Interdiffusion coefficient at peak temperature T ₀ in the phase A - D ₀ Pre-exponential factor in an Arrhenius relation - EBDC Effective binary diffusion coefficient between a solute and a multicomponent solvent matrix - FEC Fixed edge composition model - EIC Effective interdiffusion coefficient - f _i Fugacity of component i - HM Hematite-magnetite oxygen fugacity buffer - kb Kilobars - P Pressure - Q Activation energy (enthalpy) of diffusion - Extent of relaxation defined as the difference between core and rim compositions normalized to the same difference in the initial zoning profile - R Gas constant - s Cooling rate - T ₀, T _Ch Peak temperature and characteristic temperature, respectively - t Time - VEC Variable edge composition model - V ⁺ Activation volume - W _ij Simple mixture interaction parameter between i and j - W _i(EB) Effective simple mixture interaction parameter of a component i in a multicomponent solution - _ij Margules interaction parameter between i and j - X _i Mole fraction of component i - _i Activity coefficient of component i - A dimensionless variable =D t/a ² - _ij Kronecker delta (i=j, _ij =1; ij, _ij =0) - Z_i Charge on the ion i  相似文献   

Characterization of agroecosystem based on land utilization indices using remote sensing and GIS     

Indrani Choudhury  M. Chakraborty  S. C. Santra  J. S. Parihar 《Journal of the Indian Society of Remote Sensing》2006,34(1):23-37

Information on various agricultural resource parameters at various levels is essential for proper management and efficient resource allocation for sustainable agricultural development. Limitations in ground-based method have encouraged the use of satellite data coupled with geographical information system (GIS) in providing spatial as well as temporal information over large and inaccessible areas. In the present study, an attempt has been made to generate raster maps using remote sensing and GIS techniques to characterize the agroecosystem of South 24 Paraganas district of West Bengal, based on land utilization indices. Information on multi-season landcover derived from the analysis of the multi-temporal RADARSAT-1 SAR and IRS-ID LISS III data as well as other ancillary information in GIS environment are the basic inputs used in the study. The present analysis shows that northern and northwestern parts are more diverse in terms of agricultural intensification as compared to the southern and northeastern parts whereas the central parts show moderate density. In terms of carrying capacity, the high carrying capacity has been observed in the southern to northeastern parts whereas the northwestern and central parts show moderate and northern parts show low carrying capacity. Overall, the characterization of agroecosystem using land utilization indices can be identified as major input to formulate a management plan for sustainable agriculture with concerns for the environment.  相似文献   

Influence of rock types and structures in the development of drainage network in hard rock area   总被引：6，自引：0，他引：6  

S K Nag  Surajit Chakraborty 《Journal of the Indian Society of Remote Sensing》2003,31(1):25-35

Remote sensing techniques has proved to be an extremely useful tool in morphometric analysis and groundwater studies. Remote sensing techniques with an emphasis on lineament identifications can play a great role in groundwater prospecting in semi-arid hard rock areas of Purulia district. In the present study, morphometric analysis using remote sensing technique has been carried out in parts of Baghmundi block, Purulia district, West Bengal. The parameters worked out include Bifurcation ratio (R_b), Stream length (L_u), Form factor (R_c), Circulatory ratio (R_c), and Drainage density (D). The morphometric analysis suggests that fractured, resistant, permeable rocks cover the area, the drainage network not so affected by tectonic disturbances. Using satellite imageries of two dates of IRS, different hydrogeomorphological units have been delineated. Among different hydrogeomorphic units (i) very shallow weathered pediment and (ii) Structural hills/ residual hills/inselbergs have very poor ground water prospects, while moderately weathered pediplains and valley fills are good prospective zones for groundwater exploration.  相似文献   

Numerical simulation by a stretched-coordinate Ocean General Circulation Model: A preliminary results     

Arun Chakraborty  H. C. Upadhyaya  O. P. Sharma  Divya Jaisawal  S. K. Deb 《Meteorology and Atmospheric Physics》2003,83(3-4):197-220

Summary ?A three-dimensional Ocean General Circulation Model has been developed in stretched coordinate from scratch. The same model has been used to perform some numerical experiments to simulate the basic circulation pattern and the model variability to atmospheric forcing. For numerical simulations 72 × 25 grid points in the horizontal directions and nine (10, 30, 75, 250, 500, 1000, 1500, 2000 and 3000 m) vertical levels are considered. The lateral boundaries are set at 60° N and 60° S. The basic focus of the paper is on the demonstration of the performance of the model and its assessment by employing appropriate forcing from the outputs of an atmospheric general circulation model. Hence, the model was forced with the forcing (wind and thermodynamic) derived from the ECMWF runs from the AMIP archives. The preliminary results show the realistic simulation of basic pattern of different fields. The model simulations show that the model is able to reproduce some of the general features of the ocean, such as surface currents, surface temperature and salinity, mass transport and meridional heat transport. It is also to be noted that the model is capable to capture the El-Ni?o and La-Ni?a type events. Received April 3, 2002; revised June 6, 2002; accepted July 24, 2002 Published online: February 20, 2003  相似文献   

Multiple forecasts of kharif rice in orissa state-four year experience of fasal pilot study     

N. K. Patel  M. Chakraborty  S. Dutta  C. Patnaik  J. S. Parihar  S. C. Moharana  A. Das  B. K. Sarangi  G. Behera 《Journal of the Indian Society of Remote Sensing》2004,32(2):125-143

Considering the requirement of multiple pre-harvest crop forecasts, the concept of Forecasting Agricultural output using Space, Agrometeorology and Land based observations (FASAL) has been formulated. Development of procedure and demonstration of this technique for four in-season forecasts for kharif rice has been carried out as a pilot study in Orissa State since 1998. As the availability of cloud-free optical remote sensing data during kharif season is very poor for Orissa state, multi-date RADARSAT SCANSAR data were used for acreage estimation of kharif rice. Meteorological models have been developed for early assessment of acreage and prediction of yield at mid and late crop growth season. Four in-season forecasts were made during four kharif seasons (1998-2001); the first forecast of zone level rice acreage at the beginning of kharif crop season using meteorological models, second forecast of district level acreage at mid growth season using two-date RADARSAT SCANSAR data and yield using meteorological models, third forecast at late growth season of district level acreage using three-date RADARSAT SCANSAR data and yield using meteorological models and revised forecast incorporating field observations at maturity. The results of multiple forecasts have shown rice acreage estimation and yield prediction with deviation up to 14 and 11 per cent respectively. This study has demonstrated the potential of FASAL concept to provide inseason multiple forecasts using data of remote sensing, meteorology and land based observations.  相似文献   

Epeiric Sea Formation on Neoproterozoic Supercontinent Break-up: A Distinctive Signature in Coastal Storm Bed Amalgamation     

Subir Sarkar  Patrick G. Eriksson  Snehasis Chakraborty 《Gondwana Research》2004,7(2):313-322

Literature review underlines uncertainty in the configuration of the Neoproterozoic supercontinent, (with Rodinia and Palaeopangaea reconstructions enjoying wide support), that stems primarily from inadequate palaeomagnetic data. Nonetheless, breakup of this supercontinent at ca. 0.65 Ga was conducive for epeiric sea formation globally. In the Vindhyan basin, India, a carbonate depositing sea developed over a fluvial-aeolian plain, at approximately 0.6 Ga. The top part of the Vindhyan Supergroup, the Upper Bhander Sandstone, was, however, able to prograde because of a decline in the rate of relative sea level rise. Within this general setting, temporal increases in this rate caused storm deposition at the coastline, largely in a supralittoral setting. Bizarre amalgamation of these storm beds without erosion likely owes its origin to severe curtailment of the velocity of the downwelling flow on the very gentle, muddy coastal slopes, and is thought to be a hallmark of deposition in an open epeiric setting. The storm domination in the Bhander embayment shelf is compatible with the Palaeopangaea supercontinental configuration.  相似文献   

Orbits of a Charged Particle in a Skew Uniform Magnetic Field on Kerr Back Ground Geometry     

K.N. Mishra  D.K. Chakraborty 《Astrophysics and Space Science》1998,260(4):441-454

In this paper we discuss the particle trajectories in a uniform magnetic field superimposed on Kerr geometry. The rotation axis of the Kerr black hole makes an angle with the asymptotic magnetic field. We find that the particle is trapped for suitable initial conditions.  相似文献   

A new method of material balance evaluation in metamorphic differentiated systems     

K. R. Chakraborty 《Contributions to Mineralogy and Petrology》1977,65(1):101-110

The methods used by earlier workers for evaluating material balance in core-mantle-matrix type differentiated systems are examined in detail. It is demonstrated that these methods can be successfully employed only when the true core-mantle volume ratio is known. On geometric grounds, it is rarely possible to have a reliable estimate of this ratio from natural specimen. Consequently, the scope of balance evaluation by these methods is severely restricted. From theoretical consideration of mass transfer relations in differentiated systems, a new computational method is proposed that can be effectively employed for quantitative balance evaluation without any prior knowledge of the core-mantle volume ratio provided the chemical analyses of the core, mantle and matrix are available. This method involves the application of the following mass balance equation: $$m_1 x_1^i + m_2 x_2^i = m_0 x_0^i {\text{ (}}i = {\text{1,2}}...{\text{,}}n{\text{)}}$$ where m ₁ and m ₂ are the mass of the core and mantle respectively, m ₀ is the mass of the matrix involved in differentiation, and x ₁ ⁱ , x ₂ ⁱ , x ₀ ⁱ are the weight fractions of the component i in the core, mantle and matrix respectively. This method would also permit a quantitative estimation of the materials added to or removed from the system. Three differentiated systems previously investigated by Mehnert (1951, 1968), Loberg (1963) and Kretz (1966) are selected for balance evaluation by the proposed method and the results are compared with the published balance analyses.  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   

An unusual diagenetic structure in the Precambrian banded iron formation (BIF) of Orissa,India, and its interpretation     

K. L. Chakraborty  T. Majumder 《Mineralium Deposita》1992,27(1):55-57

An unusual type of late diagenetic tectonic and compaction structure simulating boudinage phenomena is described and documented from the Precambrian banded iron formation (BIF) of Orissa, India. The structure was seemingly initiated by the development of tension cracks in the hydroplastic stage followed by rotation and imbrication of the segments of the iron (magnetite) bands. The tension cracks were subsequently filled up by finely crystalline diagenetic quartz veins.  相似文献