The energetics of natural garnet solid solution     

Jibamitra Ganguly  George C. Kennedy 《Contributions to Mineralogy and Petrology》1974,48(2):137-148

Approximate mixing properties of the end-member components of the quarternary garnet solid solution, (Fe,Mg,Ca,Mn)₃Al₂Si₃O₁₂, have been derived through theoretical analysis of observational data, combined with certain experimental results and crystal chemical considerations. The results suggest that the mixing of pyrope with grossularite, spessartite, and almandine would involve significant positive excess free energies of mixing leading to the critical mixing temperatures of 694±55, 535±140, and 479±63 °C respectively. Spessartite would mix with almandine nearly ideally, and with grossularite with small positive deviation from ideality. The quarternary solution reduces essentially to a ternary mixture of pyrope, grossularite, and almandine + spessartite. The solid solubility relation, and tie line coordinates in this ternary system has been calculated as a function of temperature; the solid solution is found to be intrinsically stable for practically all ternary compositions at 600 °C.  相似文献   

Reaction texture and Fe-Mg zoning in granulite garnet from SØstrene Island, Antarctica: Modeling and constraint on the time scale of metamorphism during the Pan-African collisional event     

J. Ganguly  B. J. Hensen  W. Cheng 《Journal of Earth System Science》2001,110(4):305-312

Garnets from the S⊍strene island, Antarctica, show reaction textures corresponding to two metamorphic episodes, one at c. 1000 Ma (M1) and the other at c. 500 Ma (M2). The latter is associated with a Pan-African tectono-metamorphic event that has been interpreted to represent a continent-continent collision followed by extensional collapse. Reaction-diffusion modeling of the compositional zoning of garnet associated with the development of reaction texture during M2 yields a time scale of ∼ 5–16 Myr for the duration of the peak of this overprinting metamorphism at ∼ 730 ± 20‡C. The associated velocity of the reaction front is ∼∼ 5.0-1.6Μm/Myr. The inferred duration of peak metamorphism during the Pan-African event seems to be in good agreement with the available U-Pb SHRIMP ages of zircon and monazite that may be interpreted to have formed at the beginning and end stages of crystallization of granite during the metamorphic peak.  相似文献   

Time-temperature relation of mineral isochrons: a thermodynamic model, and illustrative examples for the RbSr system     

Jibamitra Ganguly  Joaquin Ruiz 《Earth and Planetary Science Letters》1987,81(4)

We have developed a thermodynamic model for the determination of the closure temperature (T_C) at which the minerals defining an internal isochron in RbSr, or similar, geochronological system were set with a geochronological clock. It is shown that the equilibrium fractionation of⁸⁷Rb and⁸⁷Sr between a pair of minerals at T_C [K_D(⁸⁷Rb⁸⁷Sr)_C] is given by the ratio of the quantity (⁸⁷Rb/⁸⁶Sr) in the two minerals as measured at the present time. K_D(⁸⁷Rb-⁸⁷Sr), which equals the element distribution coefficient K_D(RbSr) under equilibrium condition, can be calibrated as a function of temperature, and compared with the retrieved value of K_D(⁸⁷Rb⁸⁷Sr)_C in a natural pair to obtain T_C. The various mineral pairs defining an internal isochron will yield concordant or discordant values of T_C depending on whether or not they closed simultaneously with respect to the diffusion of Rb and Sr. Both types of results are expected, and are important in the analyses of the evolutionary history of the host rocks. Preliminary analyses of the published data in the RbSr system suggest a fairly wide range of T_C even for the same mineral pair, reflecting differences in the cooling rates and physico-chemical environments of the host rocks.  相似文献   

Experimental determination of cation diffusivities in aluminosilicate garnets   总被引：1，自引：0，他引：1  

Timothy P. Loomis  Jibamitra Ganguly  Stephen C. Elphick 《Contributions to Mineralogy and Petrology》1985,90(1):45-51

Data from experimentally-induced diffusion profiles at approximately 40 Kbar, 1,300–1,500° C in spessartine-almandine couples and a pyrope-almandine couple at 40 Kbar, 1,440° C, described in Part I, were used to derive tracer diffusion coefficients (D ^*) of Fe, Mn and Mg in garnet. The experimental data were fitted by numerical simulations that model multicomponent, compositionally-dependent difussion, including the effects of nonideal thermodynamic mixing. The simulations use the formalism of irreversible thermodynamics and an eigenvector technique of solution. We were able to fit the asymmetrical spessartine-almandine profiles using constant D ^* and either the Darken/Hartley-Crank or Manning-Lasaga models relating D ^* and interdiffusion coefficients, and both models yielded D _Mg ^* consistent with the direct measurement of D _Mg ^* in by Cygan and Lasaga (1985) at lower temperatures (750–900° C). The results (equations 4.1–4.3 and Table 1) indicate that D _Fe ^* D _Mg ^* <D _Mn ^* and Q _FeQ _Mg>Q _Mn, where Q is the activation energy. In contrast, the asymmetry of pyrope-almandine profiles is too great to fit with either tracer model assuming constant D ^* and indicates that D _Mg ^* is similar to its value in spessartine-almandine couples but D _Fe ^* is an order of magnitude less. The fit also suggests that D _Ca ^* < D _Fe ^* Mg ^* in pyrope-almandine couples. Synthesis of data from the two types of diffusion couples suggests that D _Mg ^* is insensitive to compositional changes, whereas D _Fe ^* is affected by Mn/Mg and Fe/Mg ratios and probably by other factors. These compositional effects on tracer coefficients are compatible with those documented by Morioka (1983) for cation diffusion in olivine.  相似文献   

Long-Term Trend in Ozone and Erythemal UV at Indian Latitudes     

Nandita D. Ganguly  K. N. Iyer 《Journal of Atmospheric Chemistry》2006,55(3):227-239

The role of atmospheric ozone to protect the living organisms and vegetation from the harmful effects of ultraviolet irradiation is well known. Depletion of the ozone layer is a great threat to the human society. In this paper we have discussed the lethal effects of ozone depletion and have presented the ozone and UV-B scenarios from 1979 to 2005 at different Indian latitudes using satellite data. The erythemal UV irradiance data obtained from Nimbus-7 and Earth probe total ozone mapping spectrometer (TOMS) and the tropospheric and stratospheric ozone data obtained from the convective cloud differential (CCD) method have been used to study the variability of erythemal UV irradiance and the stratospheric and tropospheric column ozone, respectively, over a period from 1979 to 2005. The observed results along with the expected upper and lower tolerance limits for tropospheric and stratospheric ozone, respectively, for different Indian latitudes, which have been estimated statistically using monthly mean CCD ozone data from 1979 to 2005 have been discussed in detail.  相似文献   

Derek W.G. Sears, The Origin of Chondrules and Chondrites, XII, 209 Seiten, 64 Abbildungen, 17 Tabellen, Literatur- und Inhaltsverzeichnis, Cambridge University Press, Cambridge, ISBN 0-521-83603-4, 2004 (£65.00, US$ 110.00 Hardback).     

Hanns-Peter Brückner 《Chemie der Erde / Geochemistry》2006,66(2):669-160

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Geospatial–temporal dependence among weekly precipitation extremes with applications to observations and climate model simulations in South America     

Gabriel Kuhn  Shiraj Khan  Auroop R. Ganguly  Marcia L. Branstetter   《Advances in water resources》2007,30(12):2401-2423

A quantification of the spatio-temporal dependence among precipitation extremes is important for investigating the properties of intense storms as well as flood or flash-flood related hazards. Extreme value theory has been widely applied to the hydrologic sciences and hydraulic engineering. However, rigorous approaches to quantify dependence structures among extreme values in space and time have not been reported in the literature. Previous researchers have quantified the dependence among extreme values through the concept of (pairwise bivariate) tail dependence coefficients. For estimation of the tail dependence coefficients, we apply a recently developed method [Kuhn G. On dependence and extremes. PhD thesis (Advisor: C. Klüppelberg), Munich University of Technology, 2006] which utilized the multivariate tail dependence function of a subclass of elliptical copulas. This study extends the previous approach in the context of space and time by considering pairs of spatial grids in South America and quantifying the dependence among precipitation extremes based on the time series at each spatial grid. In addition, Kendall’s τ is used to estimate the pairwise copula correlation (for an elliptical copula) of precipitation between all grids in South America. The geospatial–temporal dependence measures are applied to precipitation observations from 1940 to 2005 as well as simulations from the Community Climate System Model version 3 (CCSM3) for 1940–2099. New insights are obtained regarding the spatio-temporal dependence structures for precipitation over South America both with regard to correlation as well as tail dependence.  相似文献   

Fe²⁺–Mg fractionation between orthopyroxene and spinel: experimental calibration in the system FeO–MgO–Al₂O₃–Cr₂O₃–SiO₂, and applications     

H. P. Liermann  J. Ganguly 《Contributions to Mineralogy and Petrology》2007,154(4):491

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Hazardous area map: an approach of sustainable urban planning and industrial development—a review     

Ganguly  Madhurima  Aynyas  Rahul  Nandan  Abhishek  Mondal  Prasenjit 《Natural Hazards》2018,91(3):1385-1405

Natural Hazards - A hazard map is a map which shows about all the vulnerable regions present in any country or at any specific place or location which is affected or will be affected by natural...  相似文献   

Biogeochemical controls of arsenic occurrence and mobility in the Indian Sundarban mangrove ecosystem   总被引：1，自引：0，他引：1  

S.K. Mandal  D. Ganguly  T.K. Jana 《Marine pollution bulletin》2009,58(5):652-657

This study aims to investigate the control of arsenic distribution by biogeochemical processes in the Indian Sundarban mangrove ecosystem and the importance of this ecosystem as an arsenic source for surrounding coastal water. The As(V)/As(III) ratio was found to be significantly lower in both surface and pore waters compared to sea water, which could be attributed to biogeochemical interconversion of these arsenic forms. The biological uptake of arsenic due to primary and benthic production occurs during the post-monsoon season, and is followed by the release of arsenic during the biochemical degradation and dissolution of plankton in the pre-monsoon season. These results suggest that arsenic is immobilized during incorporation into the arsenic-bearing initial phase, and unlikely to be released into pore water until the complete microbial degradation of arsenic-bearing organic compounds.  相似文献