Jibamitra Ganguly

Interests

Research

Experimental and theoretical Petrology; Geo-/Cosmo-chemistry; Petrological Geodynamics; Application of Thermodynamics, Kinetics and Computational Quantum Chemistry to terrestrial and planetary problems.

Teaching

Geosciences; subfields: Petrology, Physical Geochemistry, Thermodynamics

Courses

No activities entered.

Scholarly Contributions

Chapters

• Singh, R. N., & Ganguly, J. (2014). Modelling paleogeotherms in the continental lithosphere: A brief review and applications to problems in the Indian subcontinent. In Modelling Magmatic and Allied Processes(pp 89-108). Heidelberg: Springer-Verlag.

Journals/Publications

• Bloch, E., & Ganguly, J. (2014). ¹⁷⁶Lu-¹⁷⁶Hf and ¹⁴⁷Sm-¹⁴³Nd ages of the Martian shergottites: Evaluation of the shock-resetting hypothesis through diffusion kinetic experiments and modeling, and petrological observations. Earth and Planetary Science Letters, 395, 173-183.
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  Abstract: We address the age controversy of the shergottite suite of Martian meteorites (~200 Ma dates determined by 176Lu-176Hf, 147Sm-143Nd, and various other decay systems as opposed to a ~4 Ga whole rock Pb-Pb date) by calculating the timescales needed to reset Hf and Nd isotopes in clinopyroxene, which is the primary host of rare earth elements amongst the minerals used to compose the 176Lu-176Hf and 147Sm-143Nd isochrons, at the peak- and post-shock P-T conditions likely to have been experienced by the shergottites. It is concluded that impact heating is highly unlikely to have significantly reset the 176Lu-176Hf and/or 147Sm-143Nd mineral isochrons of these meteorites. This conclusion is bolstered by the nature of measured concentration profiles of Cr and Fe across olivine-maskelynite boundaries, and Ti profiles across clinopyroxene-maskelynite/melt interfaces in the shergottite RBT 04262. The lack of any evidence of diffusion in the measured concentration profiles, coupled with the qualitative incompatibility of the measured crystal-melt fractionation trends at these interfaces with the nature of fractionation expected from equilibrium partitioning, provides strong evidence that no substantial chemical exchange took place between the solid and melt phases during peak-shock P-T conditions. Furthermore, we find that the compositional profiles of major elements in coexisting augite and pigeonite are homogenous and reflect a magmatic temperature of 1143 ± 9°C. We argue that the pyroxene compositions, and consequently the 176Lu-176Hf and 147Sm-143Nd geochronometers, were highly unlikely to have been reset by the thermal effect of a shock event. X-ray mapping of a selected section of RBT 04262 shows no evidence of enhanced grain boundary diffusion. We thus conclude that the ~200 Ma dates recorded by the 176Lu-176Hf and 147Sm-143Nd geochronometers most likely record the crystallization age of the shergottites. © 2014 Elsevier B.V.
• Ganguly, J., Tirone, M., Chakraborty, S., & Domanik, K. (2013). H-chondrite parent asteroid: A multistage cooling, fragmentation and re-accretion history constrained by thermometric studies, diffusion kinetic modeling and geochronological data. Geochimica et Cosmochimica Acta, 105, 206-220.
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  Abstract: We present a detailed thermometric study and cooling history analysis of selected H-chondrites from the petrologic types 4-6 on the basis of their mineralogical properties, and integrate these data with other available constraints on the cooling rates to develop a comprehensive model for the cooling, fragmentation and re-accretion history of the parent asteroid. Temperatures have been determined on the basis of two-pyroxene (2-Px) and spinel (Spnl)-orthopyroxene (Opx)/olivine (Ol) thermometers using the average of line scans and distributed spot analysis of coexisting pairs in each set. All of these minerals have been found to be compositionally homogeneous from ∼1 to 2. μm from the interface within the resolution of microprobe analysis. The thermometric results for the H5 (Allegan and Richardton) and H6 (Guarena and Kernouvé) samples are very similar. Also, while the 2-Px temperature increases by ∼90. °C from H4 to H5/6, a reverse trend is observed for the Spnl-Opx/Ol temperatures implying compositional resetting of these pairs during cooling. For the H4 sample (Forest Vale) all thermometric results are similar. The cooling rates calculated from numerical modeling of the compositional profiles in Opx-Cpx pairs in H5 and H6, corrected for the spatial averaging or convolution effect in microprobe analysis, are ∼25-100. °C/ky, which are 3-4 orders of magnitude higher than the cooling rates implied by in situ cooling in an onion-shell parent body model. Similar numerical simulation of the compositional profile in Opx-Spnl pair in H4 yields a cooling rate ∼50. °C/ky, which is in very good agreement with recent metallographic cooling rate of this sample and geochronological constraints on the cooling T-t path. Numerical simulation suggests that the slow cooling of the H5/6 samples at a rate of ∼15. °C/My, as deduced by recent metallographic study, could not have commenced at a temperature above ∼700. °C since, otherwise, the simulated compositional profile fails to match the observed profile. For the H5 samples, the T-t path constructed on the basis of Hf-W age of peak metamorphism and two stage cooling model satisfies the constraints imposed by the Pb-Pb ages of the phosphates and Ar-Ar ages of the feldspars vs. their respective closure temperatures, whereas that for H6 samples constructed using the same approach fails to satisfy these geochronological data. A second stage of even slower cooling at ∼3. °C/My needs to be invoked to satisfy the geochronological age vs. closure temperature relations. We present a model of fragmentation and re-accretion history of the parent body that could lead to the reconstructed T-t paths of the H-chondrite samples studied in this work, and discuss some of their broader implications. The cooling rates retrieved from the available data on the Fe-Mg ordering states of orthopyroxenes of some other H5 and H6 samples are orders of magnitude faster than the metallographic cooling rates that are applicable to similar low temperature domain. It is, thus, likely that all samples of the same petrologic type did not share a common cooling history. © 2012 Elsevier Ltd.
• Borinski, S. A., Hoppe, U., Chakraborty, S., Ganguly, J., & Bhowmik, S. K. (2012). Multicomponent diffusion in garnets I: General theoretical considerations and experimental data for Fe-Mg systems. Contributions to Mineralogy and Petrology, 164(4), 571-586.
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  Abstract: We have carried out a combined theoretical and experimental study of multicomponent diffusion in garnets to address some unresolved issues and to better constrain the diffusion behavior of Fe and Mg in almandine-pyrope-rich garnets. We have (1) improved the convolution correction of concentration profiles measured using electron microprobes, (2) studied the effect of thermodynamic non-ideality on diffusion and (3) explored the use of a mathematical error minimization routine (the Nelder-Mead downhill simplex method) compared to the visual fitting of concentration profiles used in earlier studies. We conclude that incorporation of thermodynamic non-ideality alters the shapes of calculated profiles, resulting in better fits to measured shapes, but retrieved diffusion coefficients do not differ from those retrieved using ideal models by more than a factor of 1.2 for most natural garnet compositions. Diffusion coefficients retrieved using the two kinds of models differ only significantly for some unusual Mg-Mn-Ca-rich garnets. We found that when one of the diffusion coefficients becomes much faster or slower than the rest, or when the diffusion couple has a composition that is dominated by one component (>75 %), then profile shapes become insensitive to one or more tracer diffusion coefficients. Visual fitting and numerical fitting using the Nelder-Mead algorithm give identical results for idealized profile shapes, but for data with strong analytical noise or asymmetric profile shapes, visual fitting returns values closer to the known inputs. Finally, we have carried out four additional diffusion couple experiments (25-35 kbar, 1,260-1,400 °C) in a piston-cylinder apparatus using natural pyrope- and almandine-rich garnets. We have combined our results with a reanalysis of the profiles from Ganguly et al. (1998) using the tools developed in this work to obtain the following Arrhenius parameters in D = D 0 exp{-[Q 1bar + (P-1)ΔV +]/RT} for D Mg* and D Fe*: Mg: Q 1bar = 228.3 ± 20.3 kJ/mol, D 0 = 2.72 (±4.52) × 10 -10 m 2/s, Fe: Q 1bar = 226.9 ± 18.6 kJ/mol, D 0 = 1.64 (±2.54) × 10 -10 m 2/s. ΔV + values were assumed to be the same as those obtained by Chakraborty and Ganguly (1992). © 2012 Springer-Verlag.
• Sano, J., Ganguly, J., Hervig, R., Dohmen, R., & Zhang, X. (2011). Neodymium diffusion in orthopyroxene: Experimental studies and applications to geological and planetary problems. Geochimica et Cosmochimica Acta, 75(16), 4684-4698.
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  Abstract: We have determined the Nd3+ diffusion kinetics in natural enstatite crystals as a function of temperature, f(O2) and crystallographic direction at 1bar pressure and applied these data to several terrestrial and planetary problems. The diffusion is found to be anisotropic with the diffusion parallel to the c-axial direction being significantly greater than that parallel to a- and b-axis. Also, D(//a) is likely to be somewhat greater than D(//b). Diffusion experiments parallel to the b-axial direction as a function of f(O2) do not show a significant dependence of D(Nd3+) on f(O2) within the range defined by the IW buffer and 1.5log unit above the WM buffer. The observed diffusion anisotropy and weak f(O2) effect on D(Nd3+) may be understood by considering the crystal structure of enstatite and the likely diffusion pathways. Using the experimental data for D(Nd3+), we calculated the closure temperature of the Sm-Nd geochronological system in enstatite during cooling as a function of cooling rate, grain size and geometry, initial (peak) temperature and diffusion direction. We have also evaluated the approximate domain of validity of closure temperatures calculated on the basis of an infinite plane sheet model for finite plane sheets showing anisotropic diffusion. These results provide a quantitative framework for the interpretation of Sm-Nd mineral ages of orthopyroxene in planetary samples. We discuss the implications of our experimental data to the problems of melting and subsolidus cooling of mantle rocks, and the resetting of Sm-Nd mineral ages in mesosiderites. It is found that a cooling model proposed earlier [Ganguly J., Yang H., Ghose S., 1994. Thermal history of mesosiderites: Quantitative constraints from compositional zoning and Fe-Mg ordering in orthopyroxene. Geochim. Cosmochim. Acta 58, 2711-2723] could lead to the observed ∼90Ma difference between the U-Pb age and Sm-Nd mineral age for mesosiderites, thus obviating the need for a model of resetting of the Sm-Nd mineral age by an "impulsive disturbance" [Prinzhoffer A, Papanastassiou D.A, Wasserburg G.J., 1992. Samarium-neodymium evolution of meteorites. Geochim. Cosmochim. Acta 56, 797-815]. © 2011 Elsevier Ltd.
• Ganguly, J. (2010). Cation diffusion kinetics in aluminosilicate garnets and geological applications. Reviews in Mineralogy and Geochemistry, 72, 559-601.
• Ottonello, G., Civalleri, B., Ganguly, J., Perger, W. F., Belmonte, D., & Zucco, M. V. (2010). Thermo-chemical and thermo-physical properties of the high-pressure phase anhydrous B (Mg₁₄Si₅O₂₄): An ab-initio all-electron investigation. American Mineralogist, 95(4), 563-573.
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  Abstract: Using the hybrid B3LYP density functional method, we computed the ab-initio thermo-chemical and -physical properties of the mineral anhydrous B (Anh-B), which has been recently suggested as a potential phase responsible for the X-discontinuity in the Earth's mantle at ∼300 km depth through the reaction forsterite + periclase = Anh-B, and also to likely split the 410 km discontinuity within the interior of a cold slab through the reaction wadsleyite/ringwoodite = Anh-B + stishovite. We first conducted an investigation of the static properties through a symmetry-preserving relaxation procedure and then computed, on the equilibrium structure, harmonic vibrational modes at the long-wavelength limit corresponding to the center of the Brillouin zone (k → 0). While optic modes are the eigenvectors of the Hessian matrix at G point, acoustic modes were obtained by solving the non-zero components of the strain matrix. Following the Kieffer model, acoustic branches were assumed to follow sine wave dispersion when traveling within the Brillouin zone. All thermodynamic properties that depend on vibrational frequencies namely, heat capacities, thermal expansion, thermal derivative of the bulk modulus, thermal correction to internal energy, enthalpy, Gibbs free energy, thermal pres-sure and Debye temperature, were computed on the basis of quasi-harmonic mode-gamma analysis of the volume effects on vibrational frequencies. Moreover, the strain tensor was used to calculate several thermo-physical properties of geophysical interest (transverse and longitudinal wave veloci-ties, shear modulus, Young's modulus, and Poisson's ratio). The ab-initio results derived in this study and the available data on molar volumes were used to calculate the univariant equilibrium forsterite + periclase = Anh-B. The results are in satisfactory agreement with the reversed experimental data of Ganguly and Frost (2006).
• Tirone, M., & Ganguly, J. (2010). Garnet compositions as recorders of P-T-t history of metamorphic rocks. Gondwana Research, 18(1), 138-146.
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  Abstract: On the basis of tests made in recent studies, we conclude that the simultaneous solutions of the equilibrium conditions of garnet-biotite Fe-Mg exchange and Grs = Plag + Aluminosilicate + Qtz (GASP) reactions, as formulated on the basis selected experimental data and well constrained thermodynamic mixing properties of garnet and plagioclase, offer robust estimates of P-T conditions of metapelitic assemblages that consist of the above minerals. Additional calculations are presented to show the compatibility of the retrieved P-T conditions of natural assemblages with the aluminosilicate phase diagram. We also calculate the minimum grain sizes of garnets that should be used for the calculation of the peak metamorphic P-T (Pp, Tp) conditions, using reasonable initial guessed values of minimum cooling rate and maximum Tp. To retrieve the thermal history of metapelites, we have developed a finite difference scheme for modeling multicomponent diffusion profiles in garnet, incorporating provisions for continuous nucleation and growth. This has been interlinked with a genetic algorithm that permits retrieval of the temperature vs. time path of metapelites through modeling of the zoning profiles in garnets, keeping several model parameters as floating variables. The numerical code has been applied to retrieve the T-t history of the low pressure-high temperature Royke metamorphic belt, Japan, by modeling the concentration profiles of Fe, Mn, Mg and Ca of garnets of different sizes that have been inferred to have developed by a process of continuous nucleation and growth. © 2010 International Association for Gondwana Research.
• Zhang, X., Ganguly, J., & Ito, M. (2010). Ca-Mg diffusion in diopside: Tracer and chemical inter-diffusion coefficients. Contributions to Mineralogy and Petrology, 159(2), 175-186.
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  Abstract: We have experimentally determined the tracer diffusion coefficients (D*) of 44Ca and 26Mg in a natural diopside (̃Di96) as function of crystallographic direction and temperature in the range of 950-1,150 °C at 1 bar and f(O2) corresponding to those of the WI buffer. The experimental data parallel to the a*, b, and c crystallographic directions show significant diffusion anisotropy in the a-c and b-c planes, with the fastest diffusion being parallel to the c axis. With the exception of logD*(26Mg) parallel to the a* axis, the experimental data conform to the empirical diffusion "compensation relation", converging to logD ̃ -19. 3 m2/s and T ̃ 1,155 °C. Our data do not show any change of diffusion mechanism within the temperature range of the experiments. Assuming that D* varies roughly linearly as a function of angle with respect to the c axis in the a-c plane, at least within a limited domain of ̃20° from the c-axis, our data do not suggest any significant difference between D*(//c) and D*(⊥(001)), the latter being the diffusion data required to model compositional zoning in the (001) augite exsolution lamellae in natural clinopyroxenes. Since the thermodynamic mixing property of Ca and Mg is highly nonideal, calculation of chemical diffusion coefficient of Ca and Mg must take into account the effect of thermodynamic factor (TF) on diffusion coefficient. We calculate the dependence of the TF and the chemical interdiffusion coefficient, D(Ca-Mg), on composition in the diopside-clinoenstatite mixture, using the available data on mixing property in this binary system. Our D*(Ca) values parallel to the c axis are about 1-1.5 log units larger than those Dimanov et al. (1996). Incorporating the effect of TF, the D(Ca-Mg) values calculated from our data at 1,100-1,200 °C is ̃0. 6-0.7 log unit greater than the experimental quasibinary D((Ca-Mg + Fe)) data of Fujino et al. (1990) at 1 bar, and ̃0.6 log unit smaller than that of Brady and McCallister (1983) at 25 kb, 1,150 °C, if our data are normalized to 25 kb using activation volume (̃4 and ̃6 cm3/mol for Mg and Ca diffusion, respectively) calculated from theoretical considerations. © Springer-Verlag 2009.
• Ganguly, J., Freed, A. M., & Saxena, S. K. (2009). Density profiles of oceanic slabs and surrounding mantle: Integrated thermodynamic and thermal modeling, and implications for the fate of slabs at the 660 km discontinuity. Physics of the Earth and Planetary Interiors, 172(3-4), 257-267.
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  Abstract: We have calculated the mineralogical properties of the Earth's mantle and the lithological units constituting the subducting oceanic slabs within a wide range of P-T conditions within the CaO-FeO-MgO-Al2O3-SiO2 system, except for the basalt top-layer of a slab, for which the system is extended to include Na2O. The mineralogical data are then converted, using the appropriate P-V-T relations, to bulk densities. The calculated adiabatic density vs. depth profile of the mantle between 200 and 725 km depths is in good agreement with geophysical and experimental data. The density data of the different compositional units are combined with calculated thermal structures for a variety of slab-mantle systems to construct equilibrium density profiles as a function of depth. The mean equilibrium densities of the slabs within the transition zone (400-660 km depth) are found to be ∼0.04-0.05 g/cm3 greater than those of the ambient mantle within the same depth interval. For the entire upper mantle, density differences between slabs and ambient mantle are slightly less, but the slabs still remain denser than the latter. At 670 km depth, slabs have lower density than the ambient lower mantle because of the commencement of perovskite forming reactions within the mantle, and displacements of these reaction boundaries to higher pressures within the slabs as a consequence of their negative P-T slopes. If perovskite forming reactions within slabs are hindered for kinetic sluggishness, then neutral buoyancy would be achieved when the slabs have penetrated ∼100 km into the lower mantle. However, using the available data on the kinetics of spinel to perovskite plus periclase reaction, we conclude that the reaction would go to completion in a Peru-type young slab (41 Myr), and very likely also in a Tonga-type old slab (110 Myr), before these penetrated 100 km into the lower mantle. Thus, slabs should always remain negatively buoyant, and therefore continue to subduct through the lower mantle once it penetrates through the 660 km discontinuity. Despite a negative buoyancy force, a slab could deflect at the top of the lower mantle (660 km) because of factors resisting subduction, namely viscosity jump, low dip angle, slab roll back, and metastable persistence of olivine in cold slabs. If published scale model experiments represent realistic approximations of the factors affecting plate subduction, then according to our density data, any slab with a dip angle of ≤40-50° would bend at the 660 km discontinuity if there is a viscosity jump of at least by a factor of ∼10 and trench migration. The basalt top-layer of a slab is denser than other slab components and the ambient mantle at all depths to 660 km, and therefore should continue to sink into the lower mantle, especially if a slab directly penetrates the 660 km barrier, instead of peeling off in the transition zone to form a "perched eclogite" or "piclogite" layer, as previously proposed. The harzburgite layer, which is sandwiched between denser basalt and lherzolite layers, faces greater resistance to subduction, especially in a young slab, and thus could significantly contribute to the deformation of a slab near the 660 km discontinuity. © 2008 Elsevier B.V. All rights reserved.
• Ottonello, G., Civalleri, B., Ganguly, J., Zuccolini, M. V., & Noel, Y. (2009). Thermophysical properties of the α-β-γ polymorphs of Mg₂SiO₄: A computational study. Physics and Chemistry of Minerals, 36(2), 87-106.
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  Abstract: Thermophysical properties of the various polymorphs (i.e. α-, β- and γ) of Mg2SiO4 were computed with the CRYSTAL06 code within the framework of CO-LCAO-GTF approach by using the hybrid B3LYP density functional method. Potential wells were calculated through a symmetry preserving, variable cell-shape structure relaxation procedure. Vibrational frequencies were computed at the long-wavelength limit corresponding to the center of the Brillouin zone (k → 0). Thermodynamic properties were estimated through a semiclassical approach that combines B3LYP vibrational frequencies for optic modes and the Kieffer's model for the dispersion relation of acoustic modes. All computed values except volume (i.e. electronic energy, zero point energy, optical vibrational modes, thermal corrections to internal energy, standard state enthalpy and Gibbs free energy of reaction, bulk modulus and its P and T derivatives, entropy, CV, CP) are consistent with available experimental data and/or reasonable estimates. Volumes are slightly overestimated relative to those determined directly by X-ray diffraction. A set of optimized volumetric properties that are consistent with the other semiclassical properties of the phases α, β and γ have been derived by optimization procedure such that the calculated boundaries for the α/β and α/β equilibria have the best overall agreement with the experimental data for these transitions. © pringer-Verlag 2008.
• Tirone, M., Ganguly, J., & Morgan, J. P. (2009). Modeling petrological geodynamics in the Earth's mantle. Geochemistry, Geophysics, Geosystems, 10(4).
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  Abstract: [1] We have developed an approach that combines principles of fluid dynamics and chemical thermodynamics into a fully coupled scheme to model geodynamic and petrological evolution of the Earth's mantle. Transport equations involving pressure, temperature, velocities, and bulk chemical composition are solved for one or more dynamic phases and interfaced with the thermodynamic solutions for equilibrium mineralogical assemblages and compositions. The mineralogical assemblage and composition are computed on a space-time grid, assuming that local thermodynamic equilibrium is effectively achieved. This approach allows us to simultaneously compute geophysical, geochemical, and petrological properties that can be compared with a large mass of observational data to gain insights into a variety of solid Earth problems and melting phenomena. We describe the salient features of our numerical scheme and the underlying mathematical principles and discuss a few selected applications to petrological and geophysical problems. First, it is shown that during the initial stage of passive spreading of plates, the composition of the melt near Earth's surface is in reasonable agreement with the average major element composition of worldwide flood basalts. Only the silica content from our model is slightly higher that in observational data. The amount of melt produced is somewhat lower than the estimated volumes for extrusive and upper crustal intrusive igneous rocks from large igneous provinces suggesting that an active upwelling of a larger mantle region should be considered in the process. Second, we have modeled a plume upwelling under a moving plate incorporating the effects of mineralogy on the density structure and viscous dissipation on the heat transport equation. The results show how these effects promote mantle instability at the base of the lithosphere. Third, we have considered a mantle convection model with viscosity and density directly related to the local equilibrium mineralogical assemblage. Interesting lateral variations and significant differences in the viscosity structure of the upper and lower mantle are revealed from our model results. The averaged viscosity variations with depth retrieved from our numerical simulations seem to reproduce the main features of the mantle viscosity structure under the Pacific ocean obtained from recent studies based on inversion of seismic data. © 2009 by the American Geophysical Union.
• Ganguly, J., Ito, M., & Zhang, X. (2007). Cr diffusion in orthopyroxene: Experimental determination, ⁵³Mn-⁵³Cr thermochronology, and planetary applications. Geochimica et Cosmochimica Acta, 71(15), 3915-3925.
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  Abstract: We have determined Cr diffusion coefficients (D) in orthopyroxene parallel to the a-, b-, and c-axial directions as a function temperature at f(O2) corresponding to those of the wüstite-iron (WI) buffer. Diffusion is found to be significantly anisotropic with D(//c) > D(//b) > D(//a), conforming to an earlier theoretical prediction. Increase of f(O2) from WI buffer conditions to 4.5 log unit above the buffer at 950 and 1050 °C leads to decrease of D(Cr) by a factor of two to three, possibly suggesting significant contribution from an interstitial diffusion mechanism. We have used the diffusion data to calculate the closure temperatures (Tc) of the Mn-Cr decay system in orthopyroxene as a function of initial temperature (T0), grain size (a) and cooling rate for spherical and plane sheet geometries. We also present graphical relations that permit retrieval of cooling rates from knowledge of the resetting of Mn-Cr ages in orthopyroxene during cooling, T0 and a. Application of these relations to the Mn-Cr age data of the cumulate eucrite Serra de Magé yields a Tc of 830-980 °C, and cooling rates of 2-27 °C/Myr at Tc and ∼1-13 °C/Myr at 500 °C. It is shown that the cooling of Serra de Magé to the closure temperature of the Mn-Cr system took place at its original site in the parent body, and thus implies a thickness for the eucrite crust in the commonly accepted HED parent body, Vesta, of greater than 30 km. This thickness of the eucrite crust is compatible only with a model of relatively olivine-poor bulk mineralogy in which olivine constitutes 19.7% of the total asteroidal mass. © 2007 Elsevier Ltd. All rights reserved.
• Liermann, H. P., & Ganguly, J. (2007). Erratum: Fe²⁺-Mg fractionation between orthopyroxene and spinel: Experimental calibration in the system FeO-MgO-Al₂ O₃-Cr₂O₃-SiO₂, and applications (Contributions Mineral Petrology vol. 145 (217-227) 10.1007/s00410-003-0444-3). Contributions to Mineralogy and Petrology, 154(4), 491-.
• Ganguly, J., & Frost, D. J. (2006). Stability of anhydrous phase B: Experimental studies and implications for phase relations in subducting slab and the X discontinuity in the mantle. Journal of Geophysical Research B: Solid Earth, 111(6).
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  Abstract: We have experimentally determined the equilibrium boundary of the reaction forsterite (Fo) + periclase (Per) = anhydrous phase B (Anh-13) at 900°-1600°C, and we used the retrieved Gibbs free energy of formation of Anh-B to calculate the stability field of Anh-B + stishovite (Sti) with respect to the Mg2SiO4 polymorphs. The results suggest the possibility of the reaction sequence wadsleytite → Anh-B + Sti→ ringwoodite with increasing pressure at temperature below ∼600°C. This might lead to an eye-shaped splitting of the 410 km discontinuity within the interior of a sufficiently cold slab, such as would prevail in a 140 Myr old slab subducting at an angle of ∼60° with a rate of ≥ 14 cm/yr (e.g., Tonga). The equilibrium boundary of Anh-B + Sti with respect to the wadsleyite and ringwoodite has, respectively, positive and negative slope in the P-T space. The reaction of Fo + Per to Anh-B seems to offer a viable explanation of the so-called X discontinuity that has been observed at 275-345 km depth in several subcontinental and subduction zone environments. It is suggested that periclase could form locally by the dissolution of silica in mantle fluid or precipitate from a hydrous melt that became enriched in MgO due to the incongruent melting of olivine at pressures of 6-8 GPa. Copyright 2006 by the American Geophysical Union.
• Ito, M., & Ganguly, J. (2006). Diffusion kinetics of Cr in olivine and ⁵³Mn-⁵³Cr thermochronology of early solar system objects. Geochimica et Cosmochimica Acta, 70(3), 799-809.
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  Abstract: We have determined the diffusion coefficient of Cr in olivine as function of temperature, oxygen fugacity (fO2), and crystallographic orientation and used these data to develop a quantitative understanding of the resetting of the short-lived 53Mn-53Cr decay system in olivine during cooling within meteorite parent body. The diffusion of Cr in olivine was found to be anisotropic, and effectively independent of fO2 between wüstite-iron buffer and two orders of magnitude above this buffer. The diffusion data were used to calculate the spatially averaged mean closure temperature of the 53Mn-53Cr decay system in olivine as function of the initial temperature, cooling rate and grain size, and also the closure age profile of this system in olivine single crystal as function of radial distance and a dimensionless parameter that incorporates the effects of various parameters that affect the closure age. We also present a thermochronolgic formulation that permits retrieval of cooling rates from the extent of resetting of the bulk 53Mn-53Cr closure age of olivine during cooling. This method was applied to determine the cooling rate of the pallasite Omolon, which showed 53Mn-53Cr bulk age of olivine that is 10 Myr younger than the age of the solar system. The calculated cooling rate, which is 20-40 °C/Myr at ∼985-1000 °C, is in good agreement with the metallographic cooling rate at ∼500 °C, when the two results are considered in terms of a cooling model in which the reciprocal temperature increases linearly with time. The inferred cooling rate of Omolon, which seems to be a sample from the core-mantle boundary, yields a burial depth of ∼30 km in a parent body of at least ∼100 km radius. © 2005 Elsevier Inc. All rights reserved.
• McCallum, I. S., Domeneghetti, M. C., Schwartz, J. M., Mullen, E. K., Zema, M., Cámara, F., McCammon, C., & Ganguly, J. (2006). Cooling history of lunar Mg-suite gabbronorite 76255, troctolite 76535 and Stillwater pyroxenite SC-936: The record in exsolution and ordering in pyroxenes. Geochimica et Cosmochimica Acta, 70(24), 6068-6078.
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  Abstract: We have determined cooling rates of orthopyroxene crystals from two Mg-suite lunar samples (gabbronorite 76255 and troctolite 76535) and one terrestrial sample (orthopyroxenite SC-936 from the Stillwater Complex), on the basis of their Fe-Mg ordering states. In addition, a cooling rate of 76255 was determined by modeling the formation of exsolution lamellae in pyroxenes. The M1-M2 site occupancies of the orthopyroxene crystals were determined by single crystal X-ray diffraction and the rate constant for the ordering reaction was used along with calibrations of the equilibrium intracrystalline fractionation of Fe and Mg as a function of temperature to calculate cooling rates. The closure temperatures (TC) of cation ordering are ∼525 °C for 76255, ∼500 °C for 76535 and ∼350 °C for SC-936 corresponding to cooling rates of ∼4 × 10-2 °C/year at the closure temperature for the lunar samples and ∼10-6 °C/year for the Stillwater sample. A cooling rate for 76255, determined by simulating the exsolution process, is 1.7 × 10-2 °C/year at a closure temperature for exsolution of 700 °C. The Fe-Mg ordering cooling rate determined for 76535 reflects a complex thermal history superimposed on the initial plutonic provenance established for this sample [McCallum, I.S., Schwartz, J.M., 2001. Lunar Mg suite: thermobarometry and petrogenesis of parental magmas. J. Geophys. Res. 106, 27969-27983]. The preservation of a crystallization age of 4.51 Ga and a metamorphic age of 4.25 Ga for 76535 is consistent with a model in which excavation of this sample from the lower lunar crust took place while the sample was at a temperature above the closure temperatures for the Sm-Nd, U-Pb and Ar-Ar isotopic systems. Temperatures in excess of the isotopic closure temperatures (i.e., >600 °C) in the lower lunar crust were maintained by heat diffusing from concentrations of U- and Th-rich KREEP material at the base of the crust. On the other hand, 76255 formed at a much shallower depth in the lunar crust (∼2 km) and was well below its isotopic closure temperatures at the time of excavation, most likely during the Serenitatis basin-forming impact event. Both lunar samples were reheated during transport to the surface and deposition in hot ejecta blankets. The reheating was short lived but apparently sufficient to redistribute Fe and Mg in M sites in orthopyroxenes. For the lunar samples, the cooling rates based on Fe-Mg ordering represent final stage cooling within an ejecta blanket. © 2006 Elsevier Inc. All rights reserved.
• Ganguly, J. (2005). Adiabatic decompression and melting of mantle rocks: An irreversible thermodynamic analysis. Geophysical Research Letters, 32(6), 1-4.
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  Abstract: The process of irreversible adiabatic decompression and melting of mantle rocks has been evaluated using the thermodynamic condition of frictionless decompression in a gravitational field. It is found that the melt productivity is significantly greater, thus enhancing the tendency for melt segregation, if a parcel of mantle rock moves upward at nearly constant velocity than that derived for the case of isentropic decompression. The T-Z trajectory of a solid mantle diapir moving upward at a constant velocity has, in general, a smaller slope than the isentropic trajectory, and assumes a negative slope when its density falls below ∼94% of that of the surrounding mantle. The acceleration of upward movement, and the overall density reduction of the material due to phase change that is the likely cause for the acceleration, have qualitatively opposite effects on the deviations of melt productivity and T-Z trajectory of mantle diapir from those under isentropic conditions. Copyright 2005 by the American Geophysical Union.
• Stimpfl, M., Ganguly, J., & Molin, G. (2005). Kinetics of Fe²⁺-Mg order-disorder in orthopyroxene: Experimental studies and applications to cooling rates of rocks. Contributions to Mineralogy and Petrology, 150(3), 319-334.
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  Abstract: We determined the forward rate constant (K+) for the Fe2+-Mg order-disorder between the M2 and M1 sites of orthopyroxene (OPx), which is described by the homogeneous reaction Fe2+ (M2) + Mg(M1) ↔ Mg(M2) + Fe2+ (M1), by both ordering and disordering experiments at isothermal condition and also by continuous cooling experiments. The rate constant was determined as a function of temperature in the range of 550-750°C, oxygen fugacity between quartz-fayalite-iron and Ni-NiO buffers, and at compositions of 16 and 50 mol% ferrosilite component. The K+ value derived from disordering experiment was found to be larger than that derived from ordering experiment at 550°C, while at T >580°C, these two values are essentially the same. The fO2 dependence of the rate constant can be described by the relation K+ α (fO2)n with n=5.5-6.5, which is compatible with the theoretically expected relation. The Arrhenius relation at the WI buffer condition is given by ln (CoK+) = -41511 - 12600XFe/T(K) + 28:26 + 5:27 XFe, min-1 where Co represents the total number of M2 + M1 sites occupied by Fe2+ and Mg per unit volume of the crystal. The above relation can be used to calculate the cooling rates of natural OPx crystals around the closure temperature (Tc) of Fe-Mg ordering, which are usually below 300°C for slowly cooled rocks. We determined the Fe-Mg ordering states of several OPx crystals (∼ Fs50) from the Central Gneissic Complex (Khtada Lake), British Columbia, which yields Tc ∼290°C. Numerical simulation of the change of Fe2+-Mg ordering in OPx as a function of temperature using the above expression of rate constant and a non-linear cooling model yields quenched values of ordering states that are in agreement with the observed values for cooling rates of 11-17°C/Myr below 300°C. The inferred cooling rate is in agreement with the available geochronological constraints. © Springer-Verlag 2005.
• Tirone, M., Ganguly, J., Dohmen, R., Langenhorst, F., Hervig, R., & Becker, H. (2005). Rare earth diffusion kinetics in garnet: Experimental studies and applications. Geochimica et Cosmochimica Acta, 69(9), 2385-2398.
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  Abstract: We determined the diffusion coefficient of Sm in almandine garnet as function of temperature at 1 bar and fO2 corresponding that of wüstite-iron buffer, and to a limited extent, that of a few other selected rare earth elements in almandine and pyrope garnets. Both garnets were demonstrated to have metastably survived the diffusion annealing at conditions beyond their stability fields. The experimental diffusion profiles were analyzed by secondary ion mass spectrometry, and in addition, by Rutherford back scattering spectroscopy for two samples. Transmission electron microscopic study of an almandine crystal that was diffusion-annealed did not reveal any near-surface fast diffusion path. Using reasonable approximations and theoretical analysis of vacancy diffusion, the experimental data were used to develop an expression of rare earth element (REE) diffusion coefficient in garnet as a function of temperature, pressure, fO2, ionic radius, and matrix composition. Calculation of the closure temperature for the Sm-Nd decay system in almandine garnet in a metamorphic terrain shows very good agreement with that constrained independently. Modeling of the REE evolution in melt and residual garnet suggests that for dry melting condition, the REE pattern in the melt should commonly conform closely to that expected for equilibrium melting. However, for much lower solidus temperatures that would prevail in the presence of a H2O-CO2 fluid, the concentration of light REE in the melt could be significantly lower than that under equilibrium melting condition. A reported core and rim differences in the REE content of a garnet crystal in a mantle xenolith in kimberlite have been reproduced by assuming that the REE zoning was a consequence of entrapment in a magma derived from an external source for ∼32,000 yr before the eruption. Copyright © 2005 Elsevier Ltd.
• Dasgupta, S., Ganguly, J., & Neogi, S. (2004). Inverted metamorphic sequence in the Sikkim Himalayas: Crystallization history, P-T gradient and implications. Journal of Metamorphic Geology, 22(5), 395-412.
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  Abstract: The metapelitic rocks of the Sikkim Himalayas show an inverted metamorphic sequence (IMS) of the complete Barrovian zones from chlorite to sillimanite + K-feldspar, with the higher grade rocks appearing at progressively higher structural levels. Within the IMS, four groups of major planar structures, S1, S2 and S3 were recognised. The S2 structures are pervasive throughout the Barrovian sequence, and are sub-parallel to the metamorphic isograds. The mineral growth in all zones is dominantly syn-S2. The disposition of the metamorphic zones and structural features show that the zones were folded as a northerly plunging antiform. Significant bulk compositional variation, with consequent changes of mineralogy, occurs even at the scale of a thin section in some garnet zone rocks. The results of detailed petrographic and thermobarometric studies of the metapelites along a roughly E-W transect show progressive increase of both pressure and temperature with increasing structural levels in the entire IMS. This is contrary to all models that call for thermal inversion as a possible reason for the origin of the IMS. Also, the observation of the temporal relation between crystallization and S2 structures is problematic for models of post-/late-metamorphic tectonic inversion by recumbent folding or thrusting. A successful model of the IMS should explain the petrological coherence of the Barrovian zones and the close relationship of crystallization in each zone with S2 planar structures along with the observed trend(s) of P-T variation in Sikkim and in other sections. A discussion is presented of some of the available models that, with some modifications, seem to be capable of explaining these observations. © 2004 Blackwell Publishing Ltd.
• Ito, M., & Ganguly, J. (2004). Potassium diffusion in melilite: Experimental studies and constraints on the thermal history and size of planetesimals hosting CAIs. Meteoritics and Planetary Science, 39(12), 1911-1919.
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  Abstract: Among the calcium-aluminum-rich inclusions (CAIs), excess 41K (41K*), which was produced by the decay of the short-lived radionuclide 41Ca (t1/2 = 0.1 Myr, has so far been detected in fassaite and in two grains of melilites. These observations could be used to provide important constraints on the thermal history and size of the planetesimals into which the CAIs were incorporated, provided the diffusion kinetic properties of K in these minerals are known. Thus, we have experimentally determined K diffusion kinetics in the melilite end-members, åkermanite and gehlenite, as a function of temperature (900-1200 °C) and crystallographic orientation at 1 bar pressure. The closure temperature of K diffusion in melilite, Tc(K:mel), for the observed grain size of melilite in the CAIs and cooling rate of 10-100 °C/Myr, as calculated from our diffusion data, is much higher than that of Mg in anorthite. The latter was calculated from the available Mg diffusion data in anorthite. Assuming that the planetesimals were heated by the decay of 26Al and 60Fe, we have calculated the size of a planetesimal as a function of the accretion time tf such that the peak temperature at a specified radial distance rc equals Tc(K:mel). The ratio (rc/R)3 defines the planetesimal volume fraction within which 41 K* in melilite grains would be at least partly disturbed, if these were randomly distributed within a planetesimal. A similar calculation was also carried out to define R versus tf relation such that 26Mg* was lost from ∼50% of randomly distributed anorthite grains, as seems to be suggested by the observational data. These calculations suggest that ∼60% of melilite grains should retain 41K* if ∼50% of anorthite grains had retained 26Mg*. Assuming that tf was not smaller than the time of chondrule formation, our calculations yield minimum planetesimal radius of ∼20-30 km, depending on the choice of planetesimal surface temperature and initial abundance of the heat producing isotope 60Fe. © Meteoritical Society, 2004.
• Ducea, M. N., Ganguly, J., Rosenberg, E. J., Patchett, P. J., Cheng, W., & Isachsen, C. (2003). Sm-Nd dating of spatially controlled domains of garnet single crystals: A new method of high-temperature thermochronology. Earth and Planetary Science Letters, 213(1-2), 31-42.
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  Abstract: Ganguly and Tirone [Meteorit. Planet. Sci. 36 (2001) 167-175] recently presented a method of determining the cooling rates of rocks from the difference between the core and bulk ages of a crystal, as determined by a single decay system. Here we present the first application of the method using the core and bulk ages of garnet single crystals, according to the Sm-Nd decay system, in two rock samples with contrasting cooling rates, which can be constrained independently. The samples belong to the metamorphic core complex, Valhalla, British Columbia, and the mid-crustal magmatic arc exposure of the Salinian terrane, California. We have micro-sampled the garnet crystals over specific radial dimensions, and measured the Nd isotopes of these small sample masses, as NdO+ via solid source mass spectrometry, to determine the Sm-Nd age difference between the core and bulk crystals. Using a peak metamorphic P-T condition of 8 ± 1 kbar, 820 ± 30°C [Spear and Parrish, J. Petrol. 37 (1996) 733-765], the core (67.3 ± 2.3 Ma) and bulk (60.9 ± 2.1 Ma) ages of the British Columbian garnet sample yield a cooling rate of 2-13°C/Myr, which is in very good agreement with the cooling rates that we have derived by modeling the retrograde Fe-Mg zoning in the same garnet, and assuming the same peak metamorphic P-T condition. Considering earlier cooling rate data derived from closure temperature vs. age relation of multiple geochronological systems [Spear and Parrish, J. Petrol. 37 (1996) 733-765], a cooling rate of ∼ 15-20°C/Myr seems most reasonable for the Valhalla complex. Diffusion kinetic analysis shows that the Sm-Nd core age of the selected garnet crystal could not have been disturbed during cooling. Consequently, the core age of the garnet crystal, 67.3 ± 2.3 Ma, corresponds to the peak metamorphic age of the Valhalla complex. The Salinian sample, on the other hand, yields indistinguishable core (78.2 ± 2.7 Ma) and bulk (77.9 ± 2.9 Ma) ages, as expected from its fast cooling history, which can be constrained by the results of earlier studies. The Sm-Nd decay system in garnet has relatively high closure temperature (usually > 650°C); therefore, the technique developed in this paper fills an important gap in thermochronology, since the commonly used thermochronometers are applicable only at lower temperatures. Simultaneous modeling of the retrograde Fe-Mg zoning in garnet, spatially resolved Sm-Nd ages of garnet single crystals, and resetting of the bulk garnet Sm-Nd age from the peak metamorphic age [Ganguly et al., Science 281 (1998) 805-807], along with additional geochronological data, would lead to robust constraints on cooling rates of rocks. © 2003 Elsevier Science B.V. All rights reserved.
• Liermann, H. P., & Ganguly, J. (2003). Fe²⁺-Mg fractionation between orthopyroxene and spinel: Experimental calibration in the system. Contributions to Mineralogy and Petrology, 145(2), 217-227.
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  Abstract: We have determined the equilibrium Fe2+ -Mg fractionation between orthopyroxene and spinel in the ferromagnesium system at 0.9-1.4 GPa, 850-1,250 °C, and also as a function of the Cr/Al ratio of spinel at 1.24 GPa, 1,000 °C. At each P-T condition, the equilibrium value of the distribution coefficient, KD(Fe-Mg), was constrained by experiments with crystalline starting mixtures, and approaching from both higher and lower initial values. The experimental data have been cast, within a thermodynamic framework, in the form of a geothermometer in the system FeO-MgO-Al2O3-Cr2O3-SiO2 (FMACrS). Using the data of O'Neill and Wall (1987) on the thermodynamic properties of Fe3+ and Ti4+ bearing spinels, we extended the thermometric formulation to account for the effect of these components. However, practical application of the extended formulation is beset with the problem of accurate determination of Fe3+ content of natural minerals. Using published data, the thermometric formulation in the FMACrS system has been applied to a number of natural assemblages that have small Fe3+ content. The retrieved temperatures are generally higher, on the average by ∼60 °C, than those obtained from the olivine-spinel Fe2+ -Mg exchange thermometer of O'Neill and Wall, as modified by Ballhaus et al. (1991), but are more compatible with the original temperature estimates by the authors of the publications. The smaller Fe2+ -Mg interdiffusion coefficient, D(Fe-Mg), in orthopyroxene compared with those in both olivine and spinel is expected to yield higher temperatures from orthopyroxene-spinel than from olivine-spinel thermometry.
• Liermann, H., & Ganguly, J. (2002). Diffusion kinetics of Fe²⁺ and Mg in aluminous spinel: Experimental determination and applications. Geochimica et Cosmochimica Acta, 66(16), 2903-2913.
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  Abstract: The diffusion coefficients of Fe2+ and Mg in aluminous spinel at ∼20 kb, 950 to 1325°C, and at 30 kb, 1125°C have been determined via diffusion couple experiments and numerical modeling of the induced diffusion profiles. The oxygen fugacity, fO2, was constrained by graphite encapsulating materials. The retrieved self-diffusion coefficients of Fe2+ and Mg at ∼20 kb, 950 to 1325°C, fit well the Arrhenian relation, D = Doexp(-Q/RT), where Q is the activation energy, with Do(Fe) = 1.8 (±2.8) × 10-5, Do(Mg) = 1.9 (±1.4) × 10-5 cm2/s, Q(Fe) = 198 ± 19, and Q(Mg) = 202 ± 8 kJ/mol. Comparison with the data at 30 kb suggests an activation volume of ∼5 cm3/mol. From analysis of compositional zoning in natural olivine-spinel assemblages in ultramafic rocks, previous reports concluded that D(Fe-Mg) in spinel with Cr/(Cr + Al) ≤0.5 is ∼10 times that in olivine. The diffusion data in spinel and olivine have been applied to the problems of preservation of Mg isotopic inhomogeneity in spinel within the plagioclase-olivine inclusions in Allende meteorite and cooling rates of terrestrial ultramafic rocks. Copyright © 2002 Elsevier Science Ltd.
• Ganguly, J., & Tirone, M. (2001). Relationship between cooling rate and cooling age of a mineral: Theory and applications to meteorites. Meteoritics and Planetary Science, 36(1), 167-175.
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  Abstract: We reviewed here the recent development on the mathematical formulation of closure temperature of a cooling geochronological system, which permits direct retrieval of cooling rate from cooling age when the diffusion parameters, grain size and initial temperature are known. This formulation is used to show how the cooling rate can be retrieved by comparing the core and bulk age of a mineral determined by a single decay system. The cooling rates of seven H chondrites of the metamorphic types H4, H5 and H6 were retrieved from the available data on the Pb-Pb model ages of the phosphates and the diffusion kinetic data of Pb in apatite. The results are in excellent agreement with the metallographic cooling rates and show an inverse relation with the metamorphic grade of these chondrites. We also addressed the problem of ∼90 Ma younger Sm-Nd mineral isochron age, defined by orthopyroxene, phosphate and plagioclase, of the Morristown mesosiderite compared to the Pb-Pb age of the Estherville mesosiderite. It is shown that this younger age could have been a consequence of resetting during cooling instead of an "impulsive heating" event, as suggested earlier.
• Ganguly, J., Hensen, B. J., & Cheng, W. (2001). 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. Proceedings of the Indian Academy of Sciences, Earth and Planetary Sciences, 110(4), 305-312.
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  Abstract: Garnets from the Søtrene 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 ∼ ∼ 5.0-1.6 μm/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.
• Liermann, H. -., & Ganguly, J. (2001). Compositional properties of coexisting orthopyroxene and spinel in some Antarctic diogenites: Implications for thermal history. Meteoritics and Planetary Science, 36(1), 155-166.
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  Abstract: We analyzed the compositional profiles of coexisting orthopyroxenes and spinels in six diogenite samples from the Antarctic meteorite collection and used the data to constrain their thermal histories. The closure temperatures of Fe2+-Mg exchange between spinel and orthopyroxene in these samples vary between ∼630 and 830 °C. However, those in other diogenite samples, for which the compositional data are available in the literature, extend up to ∼1125 °C. This wide range of closure temperatures suggests repeated excavation of the diogenites from their original sites over a long time interval during cooling. The orthopyroxene grains were found to be homogeneous in composition while two of the relatively large spinel grains in the samples Elephant Moraine (EET) 87530 and Thiel Mountains (TIL) 82410 showed compositional zoning near the rim. Modeling of the spinel zoning in TIL 82410 suggests that it developed during cooling under a regolith or ejecta blanket, possibly at a depth of ∼80-120 m, and that the spinel composition was homogeneous at ∼900 °C. A nonlinear cooling model in which the cooling rate is given by ηT(K)2, with η=5.8 X 10-3 K-1Ma-1, leads to simulated retrograde zoning profile in spinel which match the observed profile in TIL 82410 very well.
• Ganguly, J., & Stimpfl, M. (2000). Cation ordering in orthopyroxenes from two stony-iron meteorites: Implications for cooling rates and metal-silicate mixing. Geochimica et Cosmochimica Acta, 64(7), 1291-1297.
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  Abstract: We have determined the cooling rates of orthopyroxene crystals from two group IVA stony iron meteorites-Steinbach (ST) and Sao Joao Nepomuceno (SJN)-on the basis of their Fe-Mg ordering states. The rate constant was calibrated as a function of temperature by controlled cooling experiments using orthopyroxene crystals separated from ST. These data were used along with earlier calibrations of the equilibrium intracrystalline fractionation of Fe and Mg as a function of temperature for crystals separated from both meteorites to calculate their cooling rates. The site occupancies of the orthopyroxene crystals were determined by single-crystal X-ray diffraction subject to the bulk compositional constraints. The closure temperatures (T(c)) of cation ordering for the untreated crystals from SJN are ~400°C, whereas those from ST vary between ~430 and 470°C. Reconciliation of the metallographic and orthopyroxene cooling rate data, within the framework of the metal-silicate mixing model of Haack et al. (1995), suggests that these two stony irons had cooled at a similar rate of ~400°C/Ma through the closure temperatures for cation ordering in the orthopyroxenes. This was followed by slow cooling for ST at ~50°C/Ma at T < 425°C. Similar slow cooling was not recorded by the metals in SJN, which implies that if this stony iron were subjected to slow cooling, it must have been below 350°C. The similar cooling rates above 425°C for both ST and SJN, as required to reconcile the metal and orthopyroxene cooling rate data, is at variance with the earlier notion (Rasmussen et al., 1995) of distinctly different cooling rates for the high and low Ni IVA irons and stony irons. The cation ordering and metallographic cooling rate data are also amenable to an alternative interpretation, which requires two different parent bodies for the two stony irons, and mixing of the metal and silicate components of ST after the metals had cooled below the closure temperature of Fe-Ni interdiffusion. However, the available textural data for ST seems to argue against such metal-silicate mixing model. Copyright (C) 2000 Elsevier Science Ltd.
• Ganguly, J., Dasgupta, S., Cheng, W., & Neogi, S. (2000). Exhumation history of a section of the Sikkim Himalayas, India: Records in the metamorphic mineral equilibria and compositional zoning of garnet. Earth and Planetary Science Letters, 183(3-4), 471-486.
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  Abstract: The exhumation history of pelitic migmatite samples from the High Himalayan Crystalline Complex (HHC) near the South Tibetian Detachment System in the Sikkim-Darjeeling section has been determined on the basis of thermobarometric analyses, retrograde breakdown reactions and compositional zoning of garnet. The peak metamorphic condition is estimated to be Ο10.4 kbar, 800°C from thermo-barometric and phase equilibrium constraints. The observed retrograde breakdown of garnet to spinel and cordierite requires near isothermal and, hence, extremely rapid (15 mm/yr) exhumation up to the depth of Ο15 km. Numerical modeling suggests that the initial rapid exhumation must have been followed by a much slower process, 2 mm/yr, up to at least 5 km depth, to lead to the development of the observed compositional zoning of garnet. The dramatic change of the exhumation velocity (Vz) might reflect a process of tectonic thinning followed by erosion and/or horizontal flow at shallow depth. Assuming that the Vz did not change significantly below 5 km depth, these results suggest that the HHC samples studied in this work exhumed from a depth of 34 km within 8 Ma. © 2000 Elsevier Science B.V. All rights reserved.
• Ganguly, J., & Tirone, M. (1999). Diffusion closure temperature and age of a mineral with arbitrary extent of diffusion: Theoretical formulation and applications. Earth and Planetary Science Letters, 170(1-2), 131-140.
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  Abstract: The commonly used expression of the closure temperature, T(C), of a diffusing species in a mineral, as derived by M.H. Dodson [Contrib. Mineral. Petrol. 40 (1973) 259-264], is applicable only to systems which have undergone sufficient diffusion so that even the composition at the center of individual grains is significantly removed from that established at the onset of cooling. We have extended Dodson's formulation to include cases with arbitrarily small amount of diffusion, and applied it to calculate T(C) and age profiles, which would develop in single crystals of different geometries. These results permit evaluation of the extent of resetting of mineral age and of ion exchange geothermometers during cooling. The measured age profile of a mineral can also be used to constrain its cooling rate. These applications have been illustrated for the cases of garnet-biotite Fe-Mg exchange geothermometer, and the cooling age and closure temperatures of the Sm-Nd and Lu-Hf decay systems in garnet.
• Stimpfl, M., Ganguly, J., & Molin, G. (1999). Fe²⁺-Mg order-disorder in orthopyroxene: Equilibrium fractionation between the octahedral sites and thermodynamic analysis. Contributions to Mineralogy and Petrology, 136(4), 297-309.
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  Abstract: The equilibrium intracrystalline distribution coefficient, k(D)(*), of Fe(*) (i.e. Fe2+ + Mn) and Mg between the M1 and M2 sites of three natural nearly binary Fe2+-Mg orthopyroxene crystals (Fs14, Fs15 and Fs49) were determined by annealing experiments at several temperatures between 550 and 1000 °C and single crystal X-ray structure refinements. In addition, the X-ray data of an orthopyroxene crystal (Fs23), which were collected earlier by Molin et al. (1991) between 700 and 1000 °C, were re-refined. The data were processed through two different refinement programs (SHELXL93 and RFINE90) using both unit and individual weights and also both ionic and atomic scattering factors. The calculated site occupancies were found to agree within their estimated standard errors. However, the use of ionic scattering factors led to significantly better goodness of fit and agreement index, and smaller standard deviations of the site occupancies than those obtained from the use of atomic scattering factors. Furthermore, the weighted refinements yielded significantly smaller standard deviations of the site occupancies than the unweighted refinements even when the same set of reflections was used in the two procedures. The site occupancy data from this study were combined with selected published data to develop expressions of k(D)(*) as a function of temperature and composition. Calculation of the excess configurational entropy, ΔS(XS), suggests that orthopyroxene should be treated as a two parameter symmetric solution instead of as a 'simple mixture'. The calculated ΔS(XS) values and the excess Gibbs free energy of mixing suggested by available cation exchange data lead to a slightly negative enthalpy of mixing in the orthopyroxene solid solution.
• Ganguly, J., Cheng, W., & Chakraborty, S. (1998). Cation diffusion in aluminosilicate garnets: Experimental determination in pyrope-almandine diffusion couples. Contributions to Mineralogy and Petrology, 131(2), 171-180.
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  Abstract: Diffusion couples made from homogeneous gem quality natural pyrope and almandine garnets were annealed within graphite capsules under anhydrous conditions at 22-40 kbar, 1057-1400 °C in a piston-cylinder apparatus. The concentration profiles that developed in each couple were modeled to retrieve the self diffusion coefficients [D(I)] of the divalent cations Fe, Mg, Mn and Ca. Because of their usually low concentions and lack of sufficient compositional change across the interface of the diffusion couples, only a few reliable data can be obtained for D(Ca) and D(Mn) from these experiments. However, nine sets of D(Fe) and D(Mg) data were retrieved in the above P-T range, and cast in the form of Arrhenian relation, D = D0 exp{-[Q(1 bar) + PΔV+]/RT}. The values of the activation energy (Q) and activation volume (ΔV+) depend on whether fO2 is constrained by graphite in the system C-O or held constant. For the first case, we have for Fe: Q(1 bar) = 65,532 ± 10,111 cal/mol, D0 = 3.50 (±2.30) × 10-5 cm2/s, ΔV+ = 5.6(±2.9) cm3/mol, and for Mg: Q(1 bar) = 60,760 ± 8,257 cal/mol, D0 = 4.66 (±2.48) × 10-5 cm2/s, ΔV+ = 5.3(±3.0) cm3/mol. Here the ΔV+ values have been taken from Chakraborty and Ganguly (1992). For the condition of constant fO2, the Q values are ∼9 kcal lower and ΔV+ values are ∼4.9 cm3/mol larger than the above values. Lower temperature extrapolation of the Arrhenian relation for D(Mg) is in good agreement with the Mg tracer diffusion dat (D*Mg) of Chakraborty and Rubie (1996) and Cygan and Lasaga (1985) at 1 bar, 750-900 °C, when all data are normalized to the same pressure and to fO2 defined by graphite in the system C-O. The D*Mg data of Schwandt et al. (1995), on the other hand, are lower by more than an order of magnitude than the low temperature extrapolation of the present data, when all data are normalized to the same pressure and to fO2 defined by the graphite buffer. Comparison of the D(Fe), D(Mg) and D(Mn) data in the pyrope-almandine diffusion couple with those in the spessartine-almandine diffusion couple of Chakraborty and Ganguly (1992) shows that the self diffusion of Fe and Mn are significantly enhanced with the increase in Mn/Mg ratio; the enhancement effect on D(Mg) is, however, relatively small. Proper application of the self diffusion data to calculate interdiffusion coefficient or D matrix elements for the purpose of modeling of diffusion processes in natural garnets must take into account these compositional effects on D(I) along with the effects of thermodynamic nonideality, fO2, and pressure.
• Ganguly, J., Tirone, M., & Hervig, R. L. (1998). Diffusion kinetics of samarium and neodymium in garnet, and a method for determining cooling rates of rocks. Science, 281(5378), 805-807.
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  Abstract: Experimental determinations of the diffusion coefficients of samarium and neodymium in almandine garnet and theoretical considerations show that one cannot assign a sufficiently restricted range of closure temperature, T(c), to the samarium-neodymium decay system in garnet for the purpose of constraining the cooling rate. However, it is shown that the samarium- neodymium cooling age of garnet can be used to calculate both cooling rate and T(c) if the temperature and age at the peak metamorphic conditions are known.
• Ganguly, J., Cheng, W., & Tirone, M. (1997). Thermodynamics of aluminosilicate garnet solid solution: New experimental data, an optimized model, and thermometric applications. Contributions to Mineralogy and Petrology, 126(1-2), 137-151.
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  Abstract: We have experimentally determined the displacement of the equilibrium Grossular + 2 Kyanite + Quartz ⇄ 3 Anorthite (GASP) as a function of garnet composition in the systems Mg-Ca-Mn, Fe-Mg-Ca and Fe-Mg-Ca-Mn at 1000°C. The results were treated along with selected experimental and observational data available in the literature as well as binary parameters from other workers to obtain a set of mutually compatible binary mixing parameters of the quaternary (Fe,Mg,Ca,Mn)- aluminosilicate garnet solid solution. Attempts to determine equilibrium garnet composition in the GASP equilibrium in the Ca-Mg binary were unsuccessful due to the formation of pyroxene. Calculations of binary and ternary miscibility gaps show that the P,T,X combination required for unmixing of garnet solid solution is not realized by natural samples. The solution model was applied to account for compositional effects on Fe-Mg exchange between garnet and ortho- or clinopyroxene. Applications of the revised thermometric formulations to selected natural assemblages yield P-T conditions which are much less sensitive to compositional effects compared to the other available formulations, and are consistent with independent constraints. ΔV̄ and ΔV°: Partial molar volume change and end-member molar volume change of a reaction, respectively. WijG, WijH, and WijS: Subregular free energy, enthalpic and entropie binary interaction parameter, respectively, between the components i and j. WG(i-j), WH(i-j), and Ws(i-j): Regular solution or simple mixture free energy, enthalpic and entropie interaction parameter, respectively, between the components i and j. ΔW1: W(Mg-i) - W(Fe-i). X1α: Atomic fraction of the component i in the phase α in the site of mixing.
• Ganguly, J., & Domeneghetti, M. C. (1996). Cation ordering of orthopyroxenes from the Skaergaard intrusion: Implications for the subsolidus cooling rates and permeabilities. Contributions to Mineralogy and Petrology, 122(4), 359-367.
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  Abstract: We have determined the quenched cation ordering states of five orthopyroxene crystals collected from the marginal border group and the lower zone a and b of the Skaergaard intrusion, and modeled these data to retrieve their closure temperatures (Tc) of Fe-Mg ordering and cooling rates. According to existing thermal models for the Skaergaard pluton, conductive cooling dominated the high and low temperature regimes, which were separated by an intermediate temperature regime in which the cooling was controlled primarily by convective fluid circulation. The cooling rates retrieved from the quenched cation ordering states of the orthopyroxene crystals strictly apply to temperatures around the closure temperatures of the ordering states, ∼ 340-400° C, which fall at the transition from convective to the lower temperature conductive cooling. The cooling rates obtained from the cation ordering states of orthopyroxene vary from ∼ 1 to 270 K/ka. These results agree well with a thermal model calculated using an assumed average permeability of 10-12cm2 for the pluton, but not completely with a model calculated on the basis of an average permeability of 10-13 cm2, although both values produced shifts of δ18O that are comparable to those observed in the pluton.
• Ganguly, J., Chakraborty, S., Sharp, T. G., & III, D. R. (1996). Constraint on the time scale of biotite-grade metamorphism during Acadian orogeny from a natural garnet-garnet diffusion couple. American Mineralogist, 81(9-10), 1208-1216.
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  Abstract: We have determined the concentration profiles across the interface of a natural garnetgarnet couple in a biotite-grade rock from eastern Vermont. The couple consists of a grossular-spessartine garnet that had formed during regional metamorphism associated with the Acadian orogeny on an almandine core, which had crystallized during an earlier episode of metamorphism related to the intrusion of Fairlee granite at 411 ± 5 Ma. The concentration profiles were measured by both electron microprobe and analytical transmission electron microscope, and they were modeled to retrieve the value of ∫ D(t)dt through the time that diffusion was effective but without recourse to any diffusion data. The length of the concentration profiles measured in microprobe is barely resolvable from that resulting from a convolution effect from the spatial averaging in the spot analyses. Deconvolution of the microprobe profiles yields a value of ∫ D(t)dt = 0-3.4 × 10-11 cm2, suggesting very little or no diffusion. TEM analyses of the concentration profiles, which are not subject to any significant convolution effect, show a very small but definitive diffusion zone across the interface of the garnet-garnet couple, which yields a value of ∫ D(t)dt = 7.6 × 10-12 cm2. Because D is a function of time through its dependence on temperature, this value of ∫ D(t)dt provides an important constraint on the thermal history during the regional metamorphism. As an example, we used it in conjunction with the available diffusion data for garnet to derive ∼40-50 Ma as the probable time scale for the biotite-grade metamorphism. taking into account the effects of the off-diagonal terms and thermodynamic nonideality on the diffusion process.
• Bose, K., & Ganguly, J. (1995). Experimental and theoretical studies of the stabilities of talc, antigorite and phase A at high pressures with applications to subduction processes. Earth and Planetary Science Letters, 136(3-4), 109-121.
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  Abstract: We have experimentally determined the equilibrium talc ⇄ enstatite + quartz/coesite + H2O to 40 kbar in the system MgOSiO2H2O (MSH) using both synthetic and nearly pure Mg end-member natural talc and other synthetic starting materials for the other solid phases. At 40 kbar, the equilibrium dehydration boundary lies ∼ 150°C higher than that calculated using data from the existing internally consistent thermochemical data bases. The reason for this discrepancy lies in the erroneous compressibility data of talc in the data bases. We have retrieved the compressibility of talc from the experimental phase equilibrium data, and have also calculated sereral other equilibria in the MSH system involving talc, antigorite and the dense hydrous magnesium silicate (DHMS), commonly referred to as phase A. Comparison of these equilibria with selected thermal profiles at the leading edge of young and old subducting oceanic slabs, along with the dehydration condition of basaltic amphibole and solidus of mantle peridotite, provides an explanation for the observed heights of the volcanic fronts above subducting oceanic lithosphere. Further, it is found that in cold oceanic slabs (≥ 50 Ma with subduction velocity of ≥ 10 cm/y), antigorite will transform to the DHMS phase A through a vapor conserved reaction at a depth of ∼ 200 km. Phase A will then serve as a carrier of water into the deeper mantle. © 1995.
• Bose, K., & Ganguly, J. (1995). Quartz-coesite transition revisited: reversed experimental determination at 500-1200°C and retrieved thermochemical properties. American Mineralogist, 80(3-4), 231-238.
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  Abstract: The quartz-coesite transition was determined by reversed experiments in a piston-cylinder apparatus in the range 500-1200°C. The equilibrium transition boundary can be expressed as P (kbar) = 21.945 (±0.1855) + 0.006901 (± 0.0003)T (K). It is subparallel to, but ~1.5 kbar higher than, the transition boundary determined by Bohlen and Boettcher (1982). The entropy [39.56 ± 0.2 J/(mol.K)] and enthalpy of formation (-907.25 ± 0.007 kJ/mol) were also retrieved from elements of coesite at 1 bar, 298 K, from phase-equilibrium data and selected thermochemical data from the literature. From the characteristics of the hysteresis loop it is concluded that the practice of maintaining a constant nominal pressure by repeated pressure adjustment during an experiment leads to variation of pressure on the sample. -from Authors
• Ganguly, J., Singh, R. N., & Ramana, D. V. (1995). Thermal perturbation during charnockitization and granulite facies metamorphism in southern India. Journal of Metamorphic Geology, 13(3), 419-430.
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  Abstract: The steady-state lithospheric geotherm at c.1 Ga in the south Indian shield area has been deduced using the available data on the concentration of radioactive elements, and the P-T conditions of Proterozoic mantle xenoliths in the south Indian kimberlites as constraints. The geotherm was adjusted back to 2.5 Ga by keeping the surface temperature constant and calculating the temperature change at the top of convecting upper mantle. The reduced or mantle heat flux, which was treated as an adjustable parameter, was 20.9-21.3 mW/m2 at 1-2.5 Ga. Comparison of the calculated steady-state geotherm with the available P-T data of the Archaean (c. 2.5 Ga) charnockites and granulites from southern India suggests that the granulite facies metamorphism in this region had resulted from a major thermal perturbation, which was c.400°C at 25 km. -from Authors
• Bose, K., & Ganguly, J. (1994). Thermogravimetric study of the dehydration kinetics of talc. American Mineralogist, 79(7-8), 692-699.
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  Abstract: The dehydration kinetics of nearly pure talc, (Mg0.99Fe0.01)3Si4O10(OH)2, and of pure synthetic talc to enstatite and SiO2 was studied as a function of temperature between 777 and 977 °C and of grain size by thermogravimetry experiments. In the grain-size range of 15-1 μm, the rate of dehydration of talc increased with decreasing grain size, but further decrease of grain size did not significantly affect the dehydration rate. This may be caused by (1) clustering of the fine-grained particles as a result of surface charging, (2) a tradeoff between the positive effect of larger surface area and the negative effect of nucleating a larger number of product phases, or (3) both. The kinetic data can be adequately modeled by a second-order phenomenological rate law. The rate constant (k) for the size fraction of 10-15 μm of the natural talc follows an Arrhenian relation, k = 1.98 × 1014exp(- Q/RT)/min, where the activation energy Q = 372 ± 7 (σ) kJ/mol. Compared with talc of the same grain size, the synthetic talc was found to have a significantly faster dehydration rate. TEM images showed topotactic growth of enstatite on talc, with a concomitant formation of tridymite.
• Cheng, W., & Ganguly, J. (1994). Some aspects of multicomponent excess free energy models with subregular binaries. Geochimica et Cosmochimica Acta, 58(18), 3763-3767.
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  Abstract: We have shown that two of the most commonly used multicomponent formulations of excess Gibbs free energy of mixing, those by Wohl (1946, 1953) and Redlich and Kister (1948), are formally equivalent if the binaries are constrained to have subregular properties, and also that other subregular multicomponent formulations developed in the mineralogical and geochemical literature are equivalent to, or higher order extensions of, these formulations. We have also presented a compact derivation of a multicomponent subregular solution leading to the same expression as derived by Helffrich and Wood (1989). It is shown that Wohl's multicomponent formulation involves combination of binary excess free energies, which are calculated at compositions obtained by normal projection of the multicomponent composition onto the bounding binary joins, and is, thus, equivalent to the formulation developed by Muggianu et al. (1975). Finally, following the lead of Hillert (1980), we have explored the limiting behavior of regular and subregular ternary solutions when a pair of components become energetically equivalent, and have, thus, derived an expression for calculating the ternary interaction parameter in a ternary solution from a knowledge of the properties of the bounding binaries, when one of these binaries is nearly ideal. © 1994.
• Ganguly, J., & Tazzoli, V. (1994). Fe²⁺-Mg interdiffusion in orthopyroxene: retrieval from the data on intracrystalline exchange reaction. American Mineralogist, 79(9-10), 930-937.
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  Abstract: Crystal structural data of orthopyroxene suggest that Fe-Mg interdiffusion should be fastest along the c axis and slowest along the a axis and that the overall kinetics of the Fe2+-Mg fractionation, or order-disorder, between the M1 and M2 sites should be dominated by exchange along the c and b directions. Using these crystallographic constraints and a formulation of the diffusion process according to absolute reaction rate theory, an expression of the average Fe2+-Mg interdiffusion coefficient along the c and b directions of orthopyroxene in terms of the rate constant of the disordering process the equilibrium intracrystalline distribution of Fe2+ and Mg, and the average distance between the neighboring M1 and M2 sites along c and b is developed. -from Authors
• Ganguly, J., Yang, H., & Ghose, S. (1994). Thermal history of mesosiderites: Quantitative constraints from compositional zoning and Fe-Mg ordering in orthopyroxenes. Geochimica et Cosmochimica Acta, 58(12), 2711-2723.
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  Abstract: We have derived mathematical relations to calculate cooling rates from the extent of compositional zoning developed during cooling across the interface of a natural diffusion couple. These relations were used to calculate the high temperature cooling rates of the mesosiderites Lowicz and Clover Springs from the available data on compositional zoning across core-overgrowth interface of orthopyroxene grains. We have also determined the cation ordering in four selected orthopyroxene crystals from Bondoc and Estherville mesosiderites with very high precision, and used these data to calculate their low temperature cooling rates. The compositional zoning of orthopyroxene crystals reflects extremely rapid cooling rates, at least ~1°C/100 years in the temperature range 850-1150°C. However, simultaneous consideration of both metallographic and cation ordering data for Estherville, within the framework of either an asymptotic or an exponential cooling model, requires a cooling rate of ~l°C/Ma near 250°C. The cation ordering data for Bondoc, for which no metallographic data are yet available, are suggestive of even slower cooling rate, which implies excavation from a somewhat greater depth in the parent body. However, within the limits of their uncertainties, the measured site occupancies of the orthopyroxene crystals from Bondoc can be reconciled with a cooling rate similar to that of Estherville. The calculated cooling rates at both high- and low-temperatures have been used to develop a thermal evolution model of mesosiderites. The suggested model is not incompatible with an asteroidal parent body for these meteorites. Further, it is shown that the closure temperature of Ar-Ar age must be tied to the slow cooling rate below 500°C. © 1994.
• Ruzicka, A., Boynton, W. V., & Ganguly, J. (1994). Olivine coronas, metamorphism, and the thermal history of the Morristown and Emery mesosiderites. Geochimica et Cosmochimica Acta, 58(12), 2725-2741.
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  Abstract: Coronas are present on all millimeter-sized mineral clasts of olivine in the Emery and Morristown mesosiderites and are a manifestation of high-temperature (T ≈ 850-1100°C) metamorphism. These coronas formed by reaction and diffusion between olivine and a mesosiderite-like matrix assemblage. The bulk composition of the coronas can be approximated by a mixture of ≈ 10-25 wt% olivine and as 90-75 wt% metal-free matrix, except for P and Cr, which are significantly enriched in coronas. Phosphorus and Cr diffused relatively rapidly to coronas and were derived from a large volume of matrix, most likely from metal that was originally enriched in these elements prior to metamorphism. The coronas in both meteorites show a similar zone sequence, but are systematically thicker in Emery (≈800 μm wide) than in Morristown (≈350 μm wide), suggesting that Emery experienced more grain growth and more intensive metamorphism than Morristown. Textural relationships suggest that corona formation and high-temperature metamorphism occurred largely after intensive millimeter-scale brecciation and after or during metal-silicate mixing. A local equilibrium model can explain many features of the coronas, but chemical equilibrium was maintained only on a very small scale. Overgrowths are present on plagioclase in the coronas of both mesosiderites and probably formed during high-temperature metamorphism. The compositional interface between core and overgrowth plagioclase is extremely sharp, suggesting that cooling rates were ≥0.1°C/y at the peak temperature of metamorphism, consistent with high-temperature metamorphism occurring in a near-surface region of the parent body. © 1994.
• Ganguly, J., Cheng, W., & O'Neill, H. (1993). Syntheses, volume, and structural changes of garnets in the pyrope- grossular join: implications for stability and mixing properties. American Mineralogist, 78(5-6), 583-593.
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  Abstract: Eleven garnet compositions in the pyrope-grossular join were synthesized from glass starting materials by a combination of hydrothermal synthesis and recycling of most of the products at ~40 kbar, 1400°C, in graphite capsules. The lattice parameters of the synthetic garnets have been determined with a precision of 0.0002-0.0004 Å. The results show a slightly positive excess volume of mixing, which is asymmetric toward the grossular end, and can be described by a subregular or Margules formulation with WVCaMg = 0.36 ± 0.23 and WVMgCa = 1.73 ± 0.3 cm3/mol (12 O atom basis). Powder X-ray diffraction (XRD) structural refinements show linear dependence of the O positional parameters and cation to O distance in dodecahedral, octahedral, and tetrahedral sites on the Ca content of garnet. The partial molar volume of grossular in pyrope-grossular and almandine-grossular joins varies smoothly and similarly between the terminal compositions and exceeds the molar volume by
• Chakraborty, S., & Ganguly, J. (1992). Cation diffusion in aluminosilicate garnets: experimental determination in spessartine-almandine diffusion couples, evaluation of effective binary diffusion coefficients, and applications. Contributions to Mineralogy and Petrology, 111(1), 74-86.
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  Abstract: 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 DMnMn, 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. © 1992 Springer-Verlag.
• Ganguly, J. (1992). Comments on "Evaluation of thermobarometers for garnet peridotites" by A. A. Finnerty and F. R. Boyd. Geochimica et Cosmochimica Acta, 56(2), 841-842.
• Lee, H. Y., & Ganguly, J. (1988). Equilibrium compositions of coexisting garnet and orthopyroxene: Experimental determinations in the system FeO-MgO-Al₂O₃-SiO₂, and applications. Journal of Petrology, 29(1), 93-113.
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  Abstract: We have determined the Fe-Mg fractionation between coexisting garnet and orthopyroxene at 20-45 kb, 975-1400°C, and the effect of iron on alumina solubility in orthopyroxene at 25 kb, 1200°C, and 20 kb, 975°C in the FMAS system. The equilibrium compositions were constrained by experiments with crystalline starting mixtures of garnet and orthopyroxene of known initial compositions in graphite capsules. All iron was assumed to be Fe2+. A mixture of PbO with about 55 mol per cent PbF2 proved very effective as a flux.The experimental results do not suggest any significant dependence of KD on Fe/Mg ratio at T ≳ 1000°C. The lnKD vs. l/T data have been treated in terms of both linear and non-linear thermodynamic functional forms, and combined with the garnet mixing model of Ganguly & Saxena (1984) to develop geothermometric expressions relating temperature to KD and Ca and Mn concentrations in garnet.The effect of Fe is similar to that of Ca and Cr3+ in reducing the alumina solubility in orthopyroxene in equilibrium with garnet relative to that in the MAS system. Thus, the direct application of the alumina solubility data in the MAS system to natural assemblages could lead to significant overestimation of pressure, probably by about 5 kb for the relatively common garnetlherzolites with about 25 mol per cent Ca+Fe2+ in garnet and about 1 wt. per cent Al2O3 in orthopyroxene. © 1988 Oxford University Press.
• Ganguly, J., & Bhattacharya, P. K. (1987). Xenoliths in Proterozoic kimberlites from southern India: petrology and geophysical implications.. Mantle Xenoliths, 249-265.
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  Abstract: There are no published records of mantle xenoliths in basalts from India. A few relatively fresh ultrabasic and eclogite xenoliths have been recovered from the kimberlite pipes of the Wajrakarur-Lattavaram area of southern India. The mineralogy of the ultrabasic xenoliths is described; these include garnet harzburgites, lherzolites, wehrlites and olivine clinopyroxenites. Some of the garnet-bearing nodules have spinel, and most have phlogopite. The geotherms defined by the calculated P-T conditions of mineral equilibria in these ultrabasic xenoliths and in the Cretaceous xenoliths from N Lesotho, southern Africa, are very similar. This similarity implies nearly steady-state thermal conditions in the upper mantle beneath continental shield area over at least 1000 m.y. The inferred P-T regime of the Indian xenoliths also suggests that the lithosphere was = or >185 km thick during the mid-Proterozoic. The ultrabasic and eclogite xenoliths have been derived from depths of 100-180 km and 75-150 km, respectively. The chemical compositions of garnet, which include a low Ca variety, seem to suggest that the Proterozoic mantle beneath the Indian Shield was progressively more 'fertile' with increasing depth at the time of kimberlite eruption. -J.M.H.
• Ganguly, J., & Ruiz, J. (1987). Time-temperature relation of mineral isochrons: a thermodynamic model, and illustrative examples for the RbSr system. Earth and Planetary Science Letters, 81(4), 338-348.
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  Abstract: We have developed a thermodynamic model for the determination of the closure temperature (TC) 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 of 87Rb and 87Sr between a pair of minerals at TC [KD(87Rb87Sr)C] is given by the ratio of the quantity ( 87Rb 86Sr) in the two minerals as measured at the present time. KD(87Rb87Sr), which equals the element distribution coefficient KD(RbSr) under equilibrium condition, can be calibrated as a function of temperature, and compared with the retrieved value of KD(87Rb87Sr)C in a natural pair to obtain TC. The various mineral pairs defining an internal isochron will yield concordant or discordant values of TC 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 TC even for the same mineral pair, reflecting differences in the cooling rates and physico-chemical environments of the host rocks. © 1987.
• Ganguly, J., Loomis, T. P., & Elphick, S. C. (1987). Experimental determination of cation diffusivities in aluminosilicate garnets: reply to the discussion by Freer of Part I, and correction of Mn tracer diffusion data in Part II. Contributions to Mineralogy and Petrology, 97(4), 537-538.
• Ganguly, J. (1986). Disordering energy versus disorder in minerals: A phenomenological relation and application to orthopyroxene. Journal of Physics and Chemistry of Solids, 47(4), 417-420.
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  Abstract: Many minerals, such as pyroxenes and amphiboles, show nonconvergent disordering and, therefore, cannot be treated in terms of the classic Bragg and Williams theory. A simple phenomenological model has been developed that is applicable to nonconvergent disordering and reduces to the well-known Bragg and Williams relation for the energy change of disordering from the state of complete order for the special case of linear convergent disordering and 'simple mixture' behavior for the whole crystal. The model has been applied to calculate the energetic parameters of disordering in orthopyroxene from site occupancy and calorimetric data, and compared with the measured or independently derived values of these parameters. © 1986.
• Elphick, S. C., Ganguly, J., & Loomis, T. P. (1985). Experimental determination of cation diffusivities in aluminosilicate garnets - I. Experimental methods and interdiffusion data. Contributions to Mineralogy and Petrology, 90(1), 36-44.
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  Abstract: We have carried out diffusion couple experiments using pairs of single crystals of natural garnet of dissimilar compositions in the range of 30-40 Kbar, 1,300-1,500° C, and measured the induced diffusion profiles by microprobe scanning across the interface. Significant modifications to, and experimentation with, the design of the pressure cell, furnace assembly and sample geometry were needed to obtain measurable volume diffusion at controlled P-T conditions. The diffusion profiles in the pyrope-almandine couples are short enough that retrieval of diffusion data from them must await deconvolution analysis to resolve the effect of spatial averaging of the microprobe beam. However, the profiles in the spessartine-almandine couples are sufficiently long to obviate convolution analysis. They yield interdiffusion coefficients (D) at 40 Kbar of D = 0.82×10-5 exp (-53.6±4.9 Kcal/RT) cm2/s and D=1.2×10-5 exp (-57.1±8.4 Kcal/RT) cm2/s for Fe-rich and Mn-rich compositions, respectively, and an activation volume of ∼4.7 cm3/mole. Preliminary analysis of profiles in a pyrope-almandine couple at ∼40 Kbar, 1,440°C suggests Fe-Mg interdiffusion to be an order of magnitude slower that Fe-Mn interdiffusion, and to increase with Fe/Mg ratio. The interdiffusion data reported here are in sharp disagreement with those of Freer (1979) and Duckworth and Freer (in Freer 1981) on Fe-Mn and Fe-Mg interdiffusion, respectively. © 1985 Springer-Verlag.
• Ganguly, J., & Saxena, S. K. (1985). Mixing properties of aluminosilicate garnets: constraints from natural and experimental data, and applications to geothermo- barometry: clarifications.. American Mineralogist, 70(11-12), 1320-.
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  Abstract: Clarifications of garnet-biotite geothermometry and related formulations (A.M. 69-88) are presented.-J.A.Z.
• Loomis, T. P., Ganguly, J., & Elphick, S. C. (1985). Experimental determination of cation diffusivities in aluminosilicate garnets - II. Multicomponent simulation and tracer diffusion coefficients. Contributions to Mineralogy and Petrology, 90(1), 45-51.
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  Abstract: 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 DMg*consistent with the direct measurement of DMg*in by Cygan and Lasaga (1985) at lower temperatures (750-900° C). The results (equations 4.1-4.3 and Table 1) indicate that DFe*≅DMg*QMn, 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 DMg*is similar to its value in spessartine-almandine couples but DFe*is an order of magnitude less. The fit also suggests that DCa*< DFe*
• Ganguly, J., & Saxena, S. K. (1984). Mixing properties of aluminosilicate garnets: constraints from natural and experimental data, and applications to geothermo- barometry.. American Mineralogist, 69(1-2), 88-97.
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  Abstract: Data on the binary mixing properties of the (Fe,Mg,Ca)3Al2Si3O12 garnets and on the Fe-Mg partitioning between garnet and coexisting phases are reviewed, refined and critically analysed. Implications for certain multicomponent and thermobarometric calculations are discussed. -J.A.Z.
• Ganguly, J. (1982). Mg-Fe order-disorder in ferromagnesian silicates: II. Thermodynamics, kinetics, and geological applications.. Advances in Physical Geochemistry: Vol. 2, 58-99.
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  Abstract: The theory of intracrystalline distribution is outlined and the relationship between macroscopic and site-mixing properties is discussed. An analysis is made of experimental data for the kinetics of Fe2+-Mg order-disorder in pyroxenes and amphiboles; the ordering observed in natural samples is considered in terms of their cooling history. -R.A.H.
• Ganguly, J. (1982). Thermodynamics of the oxygen isotope fractionation involving plagioclase. Earth and Planetary Science Letters, 61(1), 123-126.
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  Abstract: The thermodynamic relationship between the oxygen isotope fractionation properties of plagioclase and its composition has been derived by treating plagioclase as a "reciprocal solution" consisting of independent cationic and anionic substitutions, namely (NaAl)5+⇄(CaSi)5+ and 18O⇄16O. The results show that the logarithm of the oxygen isotope fractionation factor, α, between plagioclase and a coexisting phase varies linearly with the anorthite content of plagioclase. The proportionality constant is given by the oxygen isotope fractionation factor between albite and anorthite, and has been derived from the experimental data of two groups of workers, O'Neil and Taylor [2] and Matsuhisa et al. [3], on the isotopic fractionation between each plagioclase end-member and aqueous solutions. It is found that O'Neil and Taylor's data on isotopic exchange of plagioclase end-members with only 2-3 M chloride solution, rather than with both pure water and the chloride solution, lead essentially to zero intercept of the ln α(Ab-An) vs. 1/T2 relation, in accord with Bottinga and Javoy's [10] conclusion about the oxygen isotope fractionation between two anhydrous silicates at T>500°C. © 1982.
• Ghose, S., & Ganguly, J. (1982). Mg-Fe order-disorder in ferromagnesian silicates.. Advances in physical geochemistry. Vol. 2, 3-99.
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  Abstract: The various contributions made in this field in the last two decades are critically reviewed. The authors present some of their results for the first time. The crystal-chemical details, which are necessary to understand the atomic forces governing Fe2+-Mg distribution in ferromagnesian silicates, as well as the experimental techniques commonly used to determine Fe2+-Mg distribution, are reviewed in Part I. Part II deals with the thermodynamics and kinetics of Fe2+-Mg order-disorder and their application to geological problems.-C.N.
• Lane, D. L., & Ganguly, J. (1980). Al₂O₃ solubility in orthopyroxene in the system MgO - Al₂O₃ - SiO₂: a re-evaluation, and mantle geotherm.. Journal of Geophysical Research, 85, 6963-6972.
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  Abstract: The solubility of Al2O3 in orthopyroxene coexisting with pyrope has been determined approaching the systems from high and low alumina contents, from 26 to 39 kbar and at 960o to over 1200oC, for durations of 8 to several hundred hours. The dT/dP slopes for Al content are positive and steeper in the garnet-peridotite field than in the spinel-peridotite, and the wt.% Al2O3 rises smoothly to 10 at the boundary between these fields at approx 1300oC and 25 kbar. The univariant boundary is moderately convex towards the T axis with a P minimum at 19 kbar and 840oC. The sheared garnet-lherzolite nodules in kimberlites do appear to have formed at higher P-T conditions than the granular ones.M.J.Le B.
• Ganguly, J. (1979). Garnet and clinopyroxene solid solutions, and geothermometry based on Fe-Mg distribution coefficient. Geochimica et Cosmochimica Acta, 43(7), 1021-1029.
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  Abstract: The available thermodynamic mixing data of aluminosilicate garnet and clinopyroxene have been critically reviewed, and integrated with the thermochemical and selected experimental data to express the Fe-Mg distribution coefficient (KD) between these phases as function of pressure, temperature and composition. The predicted compositional dependence of KD agrees with the available experimental and observational data. Owing to the lack of adequate data on the mixing properties of Jadeite with diopside and hedenbergite, the geothermometric application of the model has to be currently restricted to the Na-poor bulk compositions. The temperature of a variety of rocks that have equilibrated under a wide range of P-T conditions have been estimated, and found to agree, on the average within 25°C, with other reliable temperature estimates of these rocks. The latter are, however, often in sharp disagreement with the temperatures determined on the basis of Råheim and Green's (1974, Contrib. Mineral. Petrol. 48, 179-203) experimental calibration of KD as function of temperature and pressure on tholeiitic bulk composition. © 1979.
• Ganguly, J., & Ghose, S. (1979). Aluminous orthopyroxene: Order-disorder, thermodynamic properties, and petrologic implications. Contributions to Mineralogy and Petrology, 69(4), 375-385.
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  Abstract: Orthopyroxene has two tetrahedral sites, designated A and B, and two octahedral sites, M1 and M2. Crystallographic studies of synthetic and natural orthopyroxenes (opx) suggest that the tetrahedral Al is ordered nearly completely in the B site, but the octahedral Al disorders between M1 and M2 sites with a preference for M1. If the 'aluminum avoidance' principle is obeyed, then the tetrahedral Si-Al ordering limits the Al substitution in opx to 25 mol%, thus leading to an end-member stoichiometry of Mg3Al2Si3O12 instead of MgAl2SiO6. The enthalpy of formation of these two components has been deduced from the available phase equilibrium data. The thermodynamic properties of the opx solid solution approximates ideal solution behavior more closely when treated in terms of the components Mg4Si4O12(QEn)-Mg3Al2Si3O12(Py) than when expressed in terms of the components Mg2Si2O6-MgAl2SiO6. A model has been developed for the octahedral disordering of Al as function of temperature and composition. These data enable calculation of the configurational entropy and molar entropy of Al-opx; distinction has been made between the cases of completely random mixing of Al and Si in the tetrahedral B site, and of random mixing without violation of the 'aluminum avoidance' principle. The second model yields entropy of the Mg3Al2Si3O12 end member which agrees almost exactly with the value derived from phase equilibrium data. The partial molal entropies of the Orthopyroxene components 'QEn' and 'Py' can be derived from these data; their implications with respect to the P-T slopes of Al2O3 isopleths for the equilibrium of Orthopyroxene with forsterite and spinel/garnet have been discussed. © 1979 Springer-Verlag.
• Ganguly, J., & Kennedy, G. C. (1977). Solubility of K in Fe-S liquid, silicate-K-(Fe-S)^liq equilibria, and their planetary implications. Earth and Planetary Science Letters, 35(3), 411-420.
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  Abstract: Potassium has been found to have extremely limited absolute solubility in Fe-S liquid in the P-T range of 18-40 kbars, 1050-1150°C, and f{hook}O2 within the field of metallic iron. It also partitioned to certain silicate phase highly in preference to Fe-S liquid at 30 kbars, 1100°C. The dependence of the partitioning of K between solid silicate and Fe-S liquid on f{hook}O2 and compositions of mineral solid solutions has been analyzed. These experimental data, along with those of others, limit the amount of K that could fractionate in Fe-S liquid layers or a core in the early history of the moon and, thus, act as localized heat sources in its thermal history models, and also seem to argue against a chondritic abundance of potassium for the earth. The question of fractionation of enough 40K in an Fe-S liquid outer core of the earth to provide the necessary thermal energy for the geomagnetic dynamo remains unresolved. © 1977.
• Ganguly, J. (1976). The energetics of natural garnet solid solution - II. Mixing of the calcium silicate end-members. Contributions to Mineralogy and Petrology, 55(1), 81-90.
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  Abstract: Approximate mixing properties of the dominant calcium silicate end-member components of natural garnets, namely grossularite, andradite and uvarovite, have been derived through theoretical thermodynamic and crystal chemical analysis, and appropriate reduction of the available experimental data. The stability of the solid solution with respect to phase separation in the ternary system has been analyzed. Finally, a general model is presented as to the approximate mixing properties of multicomponent natural garnet solid solution involving substitutions in both eight and six coordinated sites. © 1976 Springer-Verlag.
• Ganguly, J., & Kennedy, G. C. (1974). Phase diagram of propargyl alcohol. Journal of Physics and Chemistry of Solids, 35(4), 605-.
• Ganguly, J., & Kennedy, G. C. (1974). The energetics of natural garnet solid solution - I. Mixing of the aluminosilicate end-members. Contributions to Mineralogy and Petrology, 48(2), 137-148.
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  Abstract: 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. © 1974 Springer-Verlag.
• Akella, J., Ganguly, J., Grover, R., & Kennedy, G. (1973). Melting of lead and zinc to 60 kbar. Journal of Physics and Chemistry of Solids, 34(4), 631-636.
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  Abstract: The melting curves for lead and zinc were determined to 60 kbar. Our melting data for lead is in good agreement with that of Millet up to 22 kbar, beyond which Millet's values are significantly higher than ours. The melting curve for zinc is almost linear to 60 kbar and our values are lower than the values reported by other workers. The melting relationship proposed by Kennedy as well as the Lindemann law have been examined in the light of the new melting data for these two metals. A straight line can be fitted through the Tm vs ΔV/V0 plots for zinc within the limits of experimental precision, but the data for lead shows a departure from the straight line fit. The lead melting curve is concave toward the Tm axis, as predicted by the Lindermann law and, in this respect, resembles previously studied Van der Waals solids. © 1973.
• Ganguly, J. (1973). Activity-composition relation of jadeite in omphacite pyroxene: Theoretical deductions. Earth and Planetary Science Letters, 19(2), 145-153.
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  Abstract: Theoretical considerations suggest that the activity coefficient of jadeite in natural multicomponent omphacite pyroxene can be approximated by an expression of the form RT ln γjd {reversed tilde equals} W12 (XDi + XHed) (I - XJd), where W12 is an adjustable interchange parameter in the jadeite-diopside join, and X stands for the mole fraction of the specified component in the pyroxene solid solution. Synthesis of the available experimental and observational data yields W12 {reversed tilde equals} - 1400 (± 1400) + 1.16 (± 1.16) cal/mole, suggesting a nearly ideal solution around 1100°C, and negative departure from ideality at low temperature of the jadeite-diopside solid solution. © 1973.
• Ganguly, J., & Kennedy, G. C. (1973). The melting temperature of uranium at high pressures. Journal of Physics and Chemistry of Solids, 34(12), 2272-2274.
• Ganguly, J. (1972). Staurolite stability and related parageneses: Theory, experiments, and applications. Journal of Petrology, 13(2), 335-365.
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  Abstract: The results of recent investigations on the stability limits of staurolite have been combined together with those of the present study to develop a semi-quantitative model of the P-T-fo2-X relations of staurolite±quartz±magnetite. The problem with respect to the hydroxyl content of staurolite has been analysed; it is concluded that no evidence has yet been mustered to discount the idealised stoichiometry proposed by Naray-Szabó & Sasvari (1958), at least as a limiting composition. The stability limits of staurolite±magnetite have been calculated from the experimental data for the equilibria involving quartz. Also the conditions over which the assemblage cordierite+magnetite+quartz could be stable, as well as a quantitative model for the fo2-P stability of almandine ± quartz have been deduced theoretically.An analysis is presented of the paragenetic relations of staurolite in common pelitic schists. It is suggested that the formation of staurolite at the expense of either chloritoid or chlorite, rather than the unqualified first appearance of staurolite as proposed by Winkler (1970), should define a 'staurolite-in' isograd in the range of 500-575 °C. In regional metamorphism, chloritoid, staurolite, and aluminum silicates should, under equilibrium conditions, be unstable relative to almandine in graphitic pelitic schists involving magnetite (chloritoid/staurolite/Al2SiO6+magnetite+quartz↑almandine+O2+H2O). The limits of P-T conditions over which staurolite and cordierite may coexist in natural assemblages have been deduced; it is restricted, almost entirely within the field of andalusite, between 500-700 °C, and 2-6 kbars, thus defining the range of P-T conditions for the 'low-pressure intermediate'- or 'Buchan'-type amphibolite facies discussed by Miyashiro (1961). In assemblages involving staurolite and andalusite, cordierite rather than almandine should usually be stable; the reverse holds for assemblages involving staurolite and sillimanite. © 1972 Oxford University Press.
• Ganguly, J., & Hoschek, G. (1971). A reply to Hoschek's criticisms of Ganguly (1968), and Ganguly and Newton (1968) in his article "The stability of staurolite and Chloritoid and their significance in metamorphism of Pelitic Rocks". Contributions to Mineralogy and Petrology, 31(2), 166-167.
• Ganguly, J., & Newton, R. C. (1968). Thermal stability of chloritoid at high pressure and relatively high oxygen fugacity. Journal of Petrology, 9(3), 444-466.
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  Abstract: The equilibrium conditions for the oxidation reaction of chloritoid to staurolite, magnetite, quartz, and vapor have been determined experimentally in the pressure range 10-25 kb using the hematite-magnetite buffer. At 10 kb total pressure the reaction is in equilibrium at 575° C. At 5 kb a value of 544° C was obtained by extrapolation of the high pressure results with an adjustment for the changing thermodynamic properties of water in the low pressure range.At oxygen fugacities along the nickel-nickel oxide buffer, the thermal stability of chloritoid is promoted by 50-60° C above the hematite-magnetite values. Here the breakdown products staurolite, almandine, and magnetite are probably more stable.The recently produced petrographic evidence for the oxidation breakdown of chloritoid and the relative lack of sensitivity of the reaction to moderate changes in total pressure and oxygen fugacity indicate that it may have potential as an important indicator on the temperature scale of progressive metamorphism. Several independent temperature estimates of the chloritoid breakdown event by workers in the field agree very well with the present value of about 550° C for the oxidation reaction of chloritoid to staurolite, magnetite, quartz, and vapor at the hematite-magnetite buffer in the pressure range 5-10 kb. © 1968 Oxford University Press.