A predictive thermodynamic model of garnet–melt trace element partitioning     

Wim Westrenen  Bernard J. Wood  Jonathan D. Blundy 《Contributions to Mineralogy and Petrology》2001,142(2):219-234

  相似文献   

Silicon and oxygen self diffusion in enstatite polycrystals: the Milke et al. (2001) rim growth experiments revisited     

R. Abart  K. Kunze  R. Milke  R. Sperb  W. Heinrich 《Contributions to Mineralogy and Petrology》2004,147(6):633-646

Milke et al. (Contrib Mineral Petrol 142:15–26, 2001) studied the diffusion of Si, Mg and O in synthetic polycrystalline enstatite reaction rims. The reaction rims were grown at 1,000°C and 1 GPa at the contacts between forsterite grains with normal isotopic compositions and a quartz matrix extremely enriched in ¹⁸O and ²⁹Si. The enstatite reaction rim grew from the original quartz-forsterite interface in both directions producing an inner portion, which replaced forsterite and an outer portion, which replaced quartz. Here we present new support for this statement, as the two portions of the rim are clearly distinguished based on crystal orientation mapping using electron backscatter diffraction (EBSD). Milke et al. (Contrib Mineral Petrol 142:15–26, 2001) used the formalism of LeClaire (J Appl Phys 14:351–356, 1963) to derive the coefficient of silicon grain boundary diffusion from stable isotope profiles across the reaction rims. LeClaires formalism is designed for grain boundary tracer diffusion into an infinite half space with fixed geometry. A fixed geometry is an undesired limitation in the context of rim growth. We suggest an alternative model, which accounts for simultaneous layer growth and superimposed silicon and oxygen self diffusion. The effective silicon bulk diffusivity obtained from our model is approximately equal within both portions of the enstatite reaction rim: D _Si,En ^eff =1.0–4.3×10^–16 m² s^–1. The effective oxygen diffusion is relatively slow in the inner portion of the reaction rim, D _O,En ^eff =0.8–1.4×10^–16 m² s^–1, and comparatively fast, D _O,En ^eff =5.9–11.6×10^–16 m² s^–1, in its outer portion. Microstructural evidence suggests that transient porosity and small amounts of fluid were concentrated at the quartz-enstatite interface during rim growth. This leads us to suspect that the presence of an aqueous fluid accelerated oxygen diffusion in the outer portion of the reaction rim. In contrast, silica diffusion does not appear to have been affected by the spatial variation in the availability of an aqueous fluid.

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The effect of halogens on Zr diffusion and zircon dissolution in hydrous metaluminous granitic melts   总被引：1，自引：0，他引：1  

Don R. Baker  Aida Conte  Carmela Freda  Luisa Ottolini 《Contributions to Mineralogy and Petrology》2002,142(6):666-678

Diffusion of Zr and zircon solubility in hydrous, containing approximately 4.5 wt% H₂O, metaluminous granitic melts with halogens, either 0.35 wt% Cl (LCl) or 1.2 wt% F (MRF), and in a halogen-free melt (LCO) were measured at 1.0 GPa and temperatures between 1,050 and 1,400 °C in a piston-cylinder apparatus using the zircon dissolution technique. Arrhenius equations for Zr diffusion in each hydrous melt composition are, for LCO with 4.4ǂ.4 wt% H₂O: % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacqWGebarcqGH9aqpcq % aIYaGmcqGGUaGlcqaI4aaocqaI4aaocqGHXcqScqaIWaamcqGGUaGl % cqaIWaamcqaIZaWmcqWG4baEcqaIXaqmcqaIWaamdaahaaWcbeqaai % abgkHiTiabiIda4aaakiGbcwgaLjabcIha4jabcchaWnaabmaabaWa % aSaaaeaacqGHsislcqaIXaqmcqaI0aancqaIWaamcqGGUaGlcqaIXa % qmcqGHXcqScqaIZaWmcqaIZaWmcqGGUaGlcqaI5aqoaeaacqWGsbGu % cqWGubavaaaacaGLOaGaayzkaaaaaa!571F! D = 2.88 ±0.03x10 ^{- 8} exp( [( - 140.1 ±33.9)/(RT)] )D = 2.88 \pm 0.03x10^{ - 8} \exp \left( {{{ - 140.1 \pm 33.9} \over {RT}}} \right) , for LCl with 4.5ǂ.5 wt% H₂O: % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacqWGebarcqGH9aqpcq % aIYaGmcqGGUaGlcqaIZaWmcqaIZaWmcqGHXcqScqaIWaamcqGGUaGl % cqaIWaamcqaI1aqncqWG4baEcqaIXaqmcqaIWaamdaahaaWcbeqaai % abgkHiTiabisda0aaakiGbcwgaLjabcIha4jabcchaWnaabmaabaWa % aSaaaeaacqGHsislcqaIYaGmcqaI1aqncqaI0aancqGGUaGlcqaI4a % aocqGHXcqScqaI2aGncqaI0aancqGGUaGlcqaIXaqmaeaacqWGsbGu % cqWGubavaaaacaGLOaGaayzkaaaaaa!5719! D = 2.33 ±0.05x10 ^{- 4} exp( [( - 254.8 ±64.1)/(RT)] )D = 2.33 \pm 0.05x10^{ - 4} \exp \left( {{{ - 254.8 \pm 64.1} \over {RT}}} \right) and for MRF with 4.9ǂ.3 wt% H₂O: % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacqWGebarcqGH9aqpcq % aIYaGmcqGGUaGlcqaI1aqncqaI0aancqGHXcqScqaIWaamcqGGUaGl % cqaIWaamcqaIZaWmcqWG4baEcqaIXaqmcqaIWaamdaahaaWcbeqaai % abgkHiTiabiwda1aaakiGbcwgaLjabcIha4jabcchaWnaabmaabaWa % aSaaaeaacqGHsislcqaIYaGmcqaIYaGmcqaIZaWmcqGGUaGlcqaI4a % aocqGHXcqScqaIXaqmcqaI1aqncqGGUaGlcqaI1aqnaeaacqWGsbGu % cqWGubavaaaacaGLOaGaayzkaaaaaa!5715! D = 2.54 ±0.03x10 ^{- 5} exp( [( - 223.8 ±15.5)/(RT)] )D = 2.54 \pm 0.03x10^{ - 5} \exp \left( {{{ - 223.8 \pm 15.5} \over {RT}}} \right) . Solubilities determined by the dissolution technique were reversed for LCO +4.5ǂ.5 wt% H₂O by crystallization of a Zr-enriched glass of LCO composition at 1,200 and 1,050 °C at 1.0 GPa. The solubility data were used to calculate partition coefficients of Zr between zircon and hydrous melt, which are given by the following expressions: for LCO % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacyGGSbaBcqGGUbGBcq % WGebardaqhaaWcbaGaemOwaOLaemOCaihabaGaemOEaONaemyAaKMa % emOCaiNaem4yamMaem4Ba8MaemOBa4Maei4la8IaemyBa0Maemyzau % MaemiBaWMaemiDaqhaaOGaeyypa0JaeGymaeJaeiOla4IaeGOnayJa % eG4mamZaaeWaaeaadaWcaaqaaiabigdaXiabicdaWiabicdaWiabic % daWiabicdaWaqaaiabdsfaubaaaiaawIcacaGLPaaacqGHsislcqaI % 1aqncqGGUaGlcqaI4aaocqaI3aWnaaa!5924! lnD_Zr^zircon/melt = 1.63( [10000/(T)] ) - 5.87\ln D_{Zr}^{zircon/melt} = 1.63\left( {{{10000} \over T}} \right) - 5.87 , for LCl % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacyGGSbaBcqGGUbGBcq % WGebardaqhaaWcbaGaemOwaOLaemOCaihabaGaemOEaONaemyAaKMa % emOCaiNaem4yamMaem4Ba8MaemOBa4Maei4la8IaemyBa0Maemyzau % MaemiBaWMaemiDaqhaaOGaeyypa0JaeGymaeJaeiOla4IaeGinaqJa % eG4naCZaaeWaaeaadaWcaaqaaiabigdaXiabicdaWiabicdaWiabic % daWiabicdaWaqaaiabdsfaubaaaiaawIcacaGLPaaacqGHsislcqaI % 0aancqGGUaGlcqaI3aWncqaI1aqnaaa!5920! lnD_Zr^zircon/melt = 1.47( [10000/(T)] ) - 4.75\ln D_{Zr}^{zircon/melt} = 1.47\left( {{{10000} \over T}} \right) - 4.75 and, for MRF by % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacyGGSbaBcqGGUbGBcq % WGebardaqhaaWcbaGaemOwaOLaemOCaihabaGaemOEaONaemyAaKMa % emOCaiNaem4yamMaem4Ba8MaemOBa4Maei4la8IaemyBa0Maemyzau % MaemiBaWMaemiDaqhaaOGaeyypa0JaeGymaeJaeiOla4IaeGinaqJa % eG4naCZaaeWaaeaadaWcaaqaaiabigdaXiabicdaWiabicdaWiabic % daWiabicdaWaqaaiabdsfaubaaaiaawIcacaGLPaaacqGHsislcqaI % 0aancqGGUaGlcqaI5aqocqaIXaqmaaa!591C! lnD_Zr^zircon/melt = 1.47( [10000/(T)] ) - 4.91\ln D_{Zr}^{zircon/melt} = 1.47\left( {{{10000} \over T}} \right) - 4.91 . Experiments on the same compositions, but with water contents down to 0.5 wt%, demonstrated reductions in both the diffusion coefficient of Zr and zircon solubility in the melt. The addition of halogens at the concentration levels studied to metaluminous melts has a small effect on either the diffusion of Zr in the melt, or the solubility of zircon at all water concentrations and temperatures investigated. At 800 °C, the calculated diffusion coefficient of Zr is lowest in LCl, 9᎒^-17 m² s^-1, and is highest in LCO, 4᎒^-15 m² s^-1. Extrapolation of the halogen-free solubility data to a magmatic temperature of 800 °C yields solubilities of approximately one-third of those directly measured in similar compositions, predicted by earlier studies of zircon dissolution and based upon analyses of natural rocks. This discrepancy is attributed to the higher oxygen fugacity of the experiments of this study compared with previous studies and nature, and the effect of oxygen fugacity on the structural role of iron in the melt, which, in turn, affects zircon solubility, but does not significantly affect Zr diffusion.  相似文献   

Water solubility in orthopyroxene   总被引：7，自引：0，他引：7  

Markus Rauch  Hans Keppler 《Contributions to Mineralogy and Petrology》2002,143(5):525-536

The solubility of water in pure enstatite was measured on samples synthesized at 1,100 °C and pressures to 100 kbar. Enstatite crystals were grown under water-saturated conditions from a stoichiometric mixture of high-purity SiO₂ and Mg(OH)₂. Water contents were calculated from polarized FTIR spectra measured on oriented single crystals. The water solubility in orthoenstatite increases with pressure to 867ᆷ ppm H₂O by weight at 75 kbar. At 100 kbar, in the stability field of high-clinoenstatite, a water solubility of 714ᆷ ppm was observed. The water solubility in enstatite at 1,100 °C can be described by the equation c_H2O=Af_H2O exp(-P(V/RT), where f_H2O is water fugacity, A=0.0204 ppm/bar and (V=12.3 cm³/mol. The infrared spectra of the hydrous enstatite crystals show a sharp, intense band at 3,363 cm^-1 and a broad, weaker band at 3,064 cm^-1. Both bands are strongly polarized parallel c. Most likely, pairs of protons attached to non-bridging oxygen atoms substitute for Mg²⁺. In order to investigate the effect of chemical impurities on water solubility in enstatite, an additional series of experiments was carried out with gels doped with Al, B, or Li as starting material. Whereas, the presence of Li and B had no detectable effect on water solubility, the addition of about 1 wt% Al₂O₃ increased water solubility in enstatite from 199 to 1,100 ppm at 1,100°C and 15 kbar. In the infrared spectra of these aluminous samples, additional bands occur in the range from 3,450 to 3,650 cm^-1. Similar bands are also observed in natural, aluminous orthopyroxenes and are most likely caused by protons coupled with Al according to the substitution of Al³⁺+H⁺ for Si⁴⁺. A series of hydrous annealing experiments on a natural, gem-quality aluminous enstatite from Tanzania yielded water solubilities generally consistent with the results from the synthetic model systems. The results presented here imply that pure enstatite has a similar storage capacity for water as olivine; however, aluminous orthopyroxenes in the mantle may dissolve much larger amounts of water comparable with the entire mass of the present hydrosphere. Moreover, the mechanism of aluminum substitution in orthopyroxenes, i.e., the distribution of Al between tetrahedral and octahedral sites, may be a potential probe of water fugacity.  相似文献   

Growth of multilayered polycrystalline reaction rims in the MgO–SiO<Subscript>2</Subscript> system,part II: modelling     

E. Gardés  W. Heinrich 《Contributions to Mineralogy and Petrology》2011,162(1):37-49

Part I of this contribution (Gardés et al. in Contrib Mineral Petrol, 2010) reported time- and temperature-dependent experimental growth of polycrystalline forsterite-enstatite double layers between single crystals of periclase and quartz, and enstatite single layers between forsterite and quartz. Both double and single layers displayed growth rates decreasing with time and pronounced grain coarsening. Here, a model is presented for the growth of the layers that couples grain boundary diffusion and grain coarsening to interpret the drop of the growth rates. It results that the growth of the layers is such that (Δx)² ∝ t ^1−1/n , where Δx is the layer thickness and n the grain coarsening exponent, as experimentally observed. It is shown that component transport occurs mainly by grain boundary diffusion and that the contribution of volume diffusion is negligible. Assuming a value of 1 nm for the effective grain boundary width, the following Arrhenius laws for MgO grain boundary diffusion are derived: log D _gb,0^Fo (m²/s) = −2.71 ± 1.03 and E _gb^Fo = 329 ± 30 kJ/mol in forsterite and log D _gb,0^En (m²/s) = 0.13 ± 1.31 and E _gb^En = 417 ± 38 kJ/mol in enstatite. The different activation energies are responsible for the changes in the enstatite/forsterite thickness ratio with varying temperature. We show that significant biases are introduced if grain boundary diffusion-controlled rim growth is modelled assuming constant bulk diffusivities so that differences in activation energies of more than 100 kJ/mol may arise. It is thus important to consider grain coarsening when modelling layered reaction zones because they are usually polycrystalline and controlled by grain boundary transport.  相似文献   

Thermodynamic data of lawsonite and zoisite in the system CaO–Al2O3–SiO2–H2O based on experimental phase equilibria and calorimetric work     

Klaus-Dieter Grevel  Mirko Schoenitz  Volker Skrok  Alexandra Navrotsky  Werner Schreyer 《Contributions to Mineralogy and Petrology》2001,142(3):298-308

The enthalpy of drop-solution in molten 2PbO·B₂O₃ of synthetic and natural lawsonite, CaAl₂(Si₂O₇)(OH)₂·H₂O, was measured by high-temperature oxide melt calorimetry. The enthalpy of formation determined for the synthetic material is (_fH^Oxides=-168.7Dž.4 kJ mol^-1, or (_fH⁰₂₉₈=-4,872.5dž.0 kJ mol^-1. These values are in reasonable agreement with previously published data, although previous calorimetric work yielded slightly more exothermic data and optimisation methods resulted in slightly less exothermic values. The equilibrium conditions for the dehydration of lawsonite to zoisite, kyanite and quartz/coesite at pressures and temperatures up to 5 GPa and 850 °C were determined by piston cylinder experiments. These results, other recent phase equilibrium data, and new calorimetric and thermophysical data for lawsonite and zoisite, Ca₂Al₃(SiO₄)(Si₂O₇)O(OH), were used to constrain a mathematical programming analysis of the thermodynamic data for these two minerals in the chemical system CaO-Al₂O₃-SiO₂-H₂O (CASH). The following data for lawsonite and zoisite were obtained: (_fH⁰₂₉₈ (lawsonite)=-4,865.68 kJ mol^-1 , S⁰₂₉₈ (lawsonite)=229.27 J K^-1 mol^-1 , (_fH⁰₂₉₈ (zoisite)=-6,888.99 kJ mol^-1 , S⁰₂₉₈ (zoisite)=297.71 J K^-1 mol^-1 . Additionally, a recalculation of the bulk modulus of lawsonite yielded K=120.7 GPa, which is in good agreement with recent experimental work.  相似文献   

Rare earth element diffusion in diopside: influence of temperature, pressure, and ionic radius, and an elastic model for diffusion in silicates   总被引：9，自引：2，他引：9  

James A. Van Orman  Timothy L. Grove  Nobumichi Shimizu 《Contributions to Mineralogy and Petrology》2001,141(6):687-703

Volume diffusion rates for five rare earth elements (La, Ce, Nd, Dy, and Yb) have been measured in single crystals of natural diopside at pressures of 0.1 MPa to 2.5 GPa and temperatures of 1,050 to1,450 °C. Polished, pre-annealed crystals were coated with a thin film of rare earth element oxides, then held at constant temperature and pressure for times ranging from 20 to 882 h. Diffusion profiles in quenched samples were measured by SIMS (secondary ion mass spectrometry) depth profiling. At 1 atm pressure, with the oxygen fugacity controlled near the quartz-fayalite-magnetite buffer, the following Arrhenius relations were obtained for diffusion normal to (001) (diffusion coefficient D in m²/s): log₁₀D_Yb=(-4.64ǂ.42)-(411ᆠ kJ/mol/2.303RT); log₁₀D_Dy=(-3.31ǃ.44)-(461ᆽ kJ/mol/2.303RT); log₁₀D_Nd=(-2.95DŽ.64)-(496ᇡ kJ/mol/2.303RT); log₁₀D_Ce=(-4.10ǃ.08)-(463ᆳ kJ/mol/2.303RT); log₁₀D_Lu=(-4.22DŽ.66)-(466ᇢ kJ/mol/2.303RT). Diffusion rates decrease significantly with increasing ionic radius, with La a factor of ~35 slower than Yb. The relationship between diffusivity and ionic radius is consistent with a model in which elastic strain plays a critical role in governing the motion of an ion through the crystal lattice. Activation volumes for Yb and Ce diffusion, at constant temperature and oxygen fugacity, are 9.0DŽ.0 cm³/mol and 8.9Dž.2 cm³/mol, respectively, corresponding to an order of magnitude decrease in diffusivity as pressure is increased from 0 to 3 GPa at 1,200 °C. Diffusion of Nd is such that grain-scale isotopic equilibrium in the mantle can be achieved in ~1 My under conditions near the peridotite solidus (~1,450 °C at 2.5 GPa). The equilibration time is much longer under P, T conditions of the lithospheric mantle or at the eclogite solidus (~1 Gy at 1.5 GPa and 1,150 °C). Because of the relatively strong decrease in diffusivity with pressure (two orders of magnitude between 2.5 and 15 GPa along an adiabatic temperature gradient), Nd transport in clinopyroxene will be effectively frozen at pressures approaching the transition zone, on time scales less than 100 My. Rare earth element diffusion rates are slow enough that significant disequilibrium uptake of REE by growing clinopyroxene phenocrysts may be preserved under natural conditions of basalt crystallization. The relative abundances and spatial distributions of REE in such crystals may provide a sensitive record of the cooling and crystallization history of the host lava.  相似文献   

Experimental investigation of the kinetics of Ostwald ripening of quartz in silicic melts     

Hugues Cabane  Didier Laporte  Ariel Provost 《Contributions to Mineralogy and Petrology》2001,142(3):361-373

To characterise the kinetics of Ostwald ripening of quartz, we conducted four series of experiments in systems consisting of quartz, with an initial grain size of ƹ.3 to 6 µm, in equilibrium with hydrous silicic liquids. Two series were performed with a haplogranitic liquid containing 6.5 wt% H₂O at 900 °C and 1 GPa. The third series was made in the quartz-anorthite system at water saturation, 900 °C, and 1 GPa. The last series was made in the quartz-albite system at water saturation, 800 °C, and 0.2 GPa. In all series, we observed a relatively small but systematic increase of the mean grain size of quartz, % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d , with increasing run duration, t. The largest increase was in the quartz-anorthite system: % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d increased by a factor of 4.3 after 326 h; the smallest increase was measured in the quartz-albite system: % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d increased by a factor of only ƹ.6 after 1,173 h. The experimental data yield very good linear fits in both ln t vs ln% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d and ln t vs % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d diagrams. The slopes in the ln t vs ln% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d diagrams, between 1/5 and 1/7, are, however, much smaller than the value of 1/3 predicted by the Lifshitz-Slyozov-Wagner theory for diffusion-controlled Ostwald ripening. A possible explanation for this discrepancy is that the diffusion-controlled regime in our experiments is only attained after a transient regime lasting from 20 h in series III to 100 h in series IV. A more straightforward explanation of the experimental results is that the rate-limiting mechanism for Ostwald ripening is quartz growth by surface nucleation not diffusion in the silicic liquid. Finally, we extrapolated our data to geological time scales to evaluate the importance of Ostwald ripening in natural quartz-bearing magmatic systems: (1) quartz cannot coarsen measurably by Ostwald ripening over reasonable time scales if the initial grain size is ƹ mm or more; and (2) Ostwald ripening may be very active at the end of nucleation events and result in the consumption of a significant proportion of crystalline nuclei.  相似文献   

Geochemistry of groundwater in parts of Guntur district, Andhra Pradesh, India   总被引：4，自引：0，他引：4  

N. Subba Rao 《Environmental Geology》2002,41(5):552-562

Hydrogeochemical investigations, which are significant for the assessment of water quality, have been carried out to study the sources of dissolved ions in groundwaters of some rural areas of Guntur district, Andhra Pradesh, India. Groundwaters in the area are mostly brackish. High contents of SiO₂, and Na⁺ and Cl^- ions in groundwater, in comparison with those of seawater, suggests a meteoric origin of groundwater. The high concentration of SiO₂ and various geochemical signatures reflect the weathering of minerals. However, the Na⁺+K⁺ vs Cl^- ratio suggests weathering, has occurred only to some extent. The chemistry of groundwater favours the formation of clay minerals (montmorillonite, illite and chlorite), because of evapotranspiration. The positive saturation index of CaCO₃ and the high signatures of Ma²⁺:Ca²⁺ and Na⁺:Ca²⁺ reveals the occurrence of evaporation. The evaporation enhances the concentration of ions (which occurred originally in the water) in the soils during summer. The very high % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr % 0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8 % frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaqabeaadaaakeaacqqG % tbWucqqGpbWtdaqhaaWcbaGaeeinaqdabaGaeeOmaiJaeeyla0caaa % aa!2EC5! SO₄^{2 -} {\rm SO}_{\rm 4}^{{\rm 2 - }} and Cl^- contents in some groundwaters and the occurrence of kankar (CaCO₃) in the area suggest a long history of evaporation. Greater ionic concentration in the groundwaters of post-monsoon compared with pre-monsoon indicates the increasing addition of leachates into the groundwater from the soils in the monsoon and anthropogenic activities, which leads to a deteriorating quality of groundwater. According to the Gibbs' diagrams, rock weathering, to some extent, and evaporation are the dominant phenomena responsible for the higher ionic concentrations found in groundwater. Measures that benefit sustainable management of groundwater quality are suggested in this study.  相似文献   

An evaluation of quartzite flow laws based on comparisons between experimentally and naturally deformed rocks   总被引：4，自引：0，他引：4  

Greg Hirth  Christian Teyssier  James W. Dunlap 《International Journal of Earth Sciences》2001,90(1):77-87

  相似文献   

Primary fluids entrapped at blueschist to eclogite transition: evidence from the Tianshan meta-subduction complex in northwestern China   总被引：5，自引：1，他引：5  

Jun Gao  Reiner Klemd 《Contributions to Mineralogy and Petrology》2001,142(1):1-14

Orthopyroxene and olivine exposed along the rim of a harzburgite xenolith from La Palma (Canary Islands) show polycrystalline selvages and diffusion zones that result from contact with mafic, alkaline, silica-undersaturated melts during at least 10-100 years before eruption. The zoned selvages consist of a fine-grained reaction rim towards the xenolith and a coarser grained, cumulate-like layer towards the melt contact. The diffusion zones are characterized by decreasing magnesium number from about 89-91 in the xenolith interior to 79-85 at the rims, and clearly result from Fe-Mg exchange with surrounding mafic melt. The width of the diffusion zones is 80-200 µm in orthopyroxene and 1,020-1,730 µm in olivine. Orthopyroxene also shows decreasing Al₂O₃ and Cr₂O₃ and increasing MnO and TiO₂ towards the reaction rims. Textural relations and comparisons with dissolution experiments suggest that orthopyroxene dissolution by silica-undersaturated melt essentially ceased after days to weeks of melt contact, possibly because of decreasing temperature and formation of the reaction rims. The short dissolution phase was followed by prolonged growth of diffusion zones through cation exchange between xenolith minerals and melt across the reaction rims, and by the growth of cumulus crystals. The observations indicate that orthopyroxene xenocrysts and harzburgite xenoliths can survive in mafic, silica-undersaturated, subliquidus magmas at 1,050-1,200 °C and 200-800 MPa for tens of years. Modeling and comparison of the diffusion zones indicate that the average Fe-Mg interdiffusion coefficient D_FeMg in orthopyroxene is 2 log units lower than that in olivine; at 1,130 °C and QFM-buffered oxygen fugacity, D_FeMg^opx = 3 ×10 ^{- 19}  m²  s^{- 1}D_{FeMg}^{opx} = 3 \times 10^{ - 19} \,{\rm m}^2 \,{\rm s}^{{\rm - 1}} . The new data overlap well with recently published data for D_FeMg in diopside, and indicate that D_FeMg ^opxD_{FeMg\,}^{opx} (as predicted by previous authors) may be extrapolated to higher temperatures and oxygen fugacities. It is suggested that D_FeMg ^opx D_{FeMg\,}^{opx} and D_FeMg in Mn-poor ferromagnesian garnet are similar within 0.5 log units at temperatures between 1,050 and 1,200 °C.  相似文献   

Contact Metamorphism of Serpentinite, Chloritic Blackwall and Rodingite at Paddy-Go-Easy Pass, Central Cascades, Washington   总被引：2，自引：2，他引：2  

FROST  B. RONALD 《Journal of Petrology》1975,16(1):272-313

The 2 km wide contact aureole produced from serpentinite bythe intrusion of the Mount Stuart Batholith into the IngallsComplex at Paddy-Go-Easy Pass contains the following ultramaficassemblages, in order of increasing grade: serpentine-forsterite-diopside,serpentine-forsterite-tremolite, forsterite-talc, forsterite-anthophyllite,forsterite-enstatite-anthophyllite, forsterite-enstatite-chlorite,forsterite-enstatite-spinel. Associated metarodingites displayfive metamorphic zones, the diagnostic assemblages of whichare, in increasing grade: grossular-idocrase-chlorite, grossular-diopside-chlorite,epidote-diopside-chlorite, epidote-diopside-spinel, plagioclase-grossular-diopside.Mafic hornfels in the aureole contains no orthopyroxene, indicatingthat the conditions of pyroxene hornfels facies were not reached. The breakdown of chlorite is best displayed in aluminous blackwallreaction zones around mafic inclusions in the peridotite. Attemperatures above those of the anthophyllite-out isograd, butwithin the field of forsterite+tremolite, these chlorite-richrocks react to form the assemblage: forsterite-enstatite-spinel.Calculations show that cordierite did not form as a result ofchlorite breakdown in the natural system because impurities,such as iron and chromium, displaced the equilibrium: forsterite+cordierite=enstatite+spinelto much lower pressures than the three kilobars found in thepure system. The primary chromite of the peridotite has been altered to chrome-magnetitein the serpentinite. This alteration seems to be isochemicalover the whole rock, as true chromite, formed by metamorphism,occurs at grades above that of the forsterite-enstatite-anthophylliteassemblage. Calcic amphibole in high-grade metaperidotite is tremolite,even in the presence of aluminous chromite, whereas that inmetamorphosed blackwall rock grades from tremolite into hornblende.The pattern of substitution appears to be: Mg₂Si₃(Na,K)(Al^VI)₂(Al^IV)₃.  相似文献   

Contact Metamorphism of Serpentinite, Chloritic Blackwall and Rodingite at Paddy-Go-Easy Pass, Central Cascades, Washington     

FROST  RONALD 《Journal of Petrology》1975,16(2):272-313

The 2 km wide contact aureole produced from serpentinite bythe intrusion of the Mount Stuart Batholith into the IngallsComplex at Paddy-Go-Easy Pass contains the following ultramaficassemblages, in order of increasing grade: serpentine-forsterite-diopside,serpentine-forsterite-tremolite, forsterite-talc, forsterite-anthophyllite,forsterite-enstatite-anthophyllite, forsterite-enstatite-chlorite,forsterite-enstatite-spinel. Associated metarodingites displayfive metamorphic zones, the diagnostic assemblages of whichare, in increasing grade: grossular-idocrase-chlorite, grossular-diopside-chlorite,epidote-diopside-chlorite, epidotediopside-spinel, plagioclase-grossular-diopside.Mafic hornfels in the aureole contains no orthopyroxene, indicatingthat the conditions of pyroxene hornfels facies were not reached. The breakdown of chlorite is best displayed in aluminous blackwallreaction zones around mafic inclusions in the peridotite. Attemperatures above those of the anthophyllite-out isograd, butwithin the field of forsterite+tremolite, these chlorite-richrocks react to form the assemblage: forsterite-enstatite-spinel.Calculations show that cordierite did not form as a result ofchlorite breakdown in the natural system because impurities,such as iron and chromium, displaced the equilibrium: forsterite+cordierite= enstatite+spinel to much lower pressures than the three kilobarsfound in the pure system. The primary chromite of the peridotite has been altered to chrome-magnetitein the serpentinite. This alteration seems to be isochemicalover the whole rock, as true chromite, formed by metamorphism,occurs at grades above that of the forsterite-enstatite-anthophylliteassemblage. Calcic amphibole in high-grade metaperidotite is tremolite,even in the presence of aluminous chromite, whereas that inmetamorphosed blackwall rock grades from tremolite into hornblende.The pattern of substitution appears to be: Mg₂Si₃rlhar2;(Na,K)(Al^VI)₂(Al^IV)₃.  相似文献   

Phase relations of a serpentine composition between 5 and 14 GPa: significance of clinohumite and phase E as water carriers into the transition zone   总被引：4，自引：0，他引：4  

Roland Stalder  Peter Ulmer 《Contributions to Mineralogy and Petrology》2001,140(6):754-679

Run products from high pressure experiments at 800-1,200 °C and 5-14 GPa (corresponding to depths of 150 to 420 km) on a serpentine bulk composition [close to Mg₃Si₂O₅(OH)₄] were analysed by optical microscopy, micro-Raman spectroscopy and electron microprobe. All charges exhibit strong chemical zoning. Fluid, melt and hydrous solids were mostly concentrated at the top, bottom and along the wall of the capsules. The central part of the charge was devoid of H₂O. Both fluid and hydrous magnesian phases exhibit a Mg/Si ratio higher than forsterite. In contrast, the centre of the capsule was enriched in SiO₂. The observed zoning can neither be explained by gravitational settling nor by a thermal gradient alone. Most likely the fluid was separated from the solids by surface forces and thereby established the chemical gradient by preferentially dissolving MgO. If strong chemical zoning is taken into account, the occurrence of more phases than allowed by the phase rule can be explained by separating the bulk into several domains of different bulk compositions. Results indicate that small amounts of F increase the stability field of clinohumite, Mg₉Si₄O₁₆(OH,F)₂, compared to OH-clinohumite in pure MSH previously reported. Clinohumite coexists with enstatite up to 975 °C at 5 GPa, and up to 1,100 °C at 12 GPa. At 14 GPa (close to the !/#-Mg₂SiO₄ transition) phase E becomes the most important water carrier. The new results indicate that clinohumite could be an important mantle mineral for transporting water into the Earth's transition zone due to its high thermal stability compared to other important water carriers such as serpentine and phase A.  相似文献   

Synthesis of tourmaline solid solutions in the system Na2O–MgO–Al2O3–SiO2–B2O3–H2O–HCl and the distribution of Na between tourmaline and fluid at 300 to 700 °C and 200 MPa     

G. v. Goerne  G. Franz  W. Heinrich 《Contributions to Mineralogy and Petrology》2001,141(2):160-173

Tourmaline has been synthesized hydrothermally at 200 MPa between 300 and 700 °C from oxide mixtures with Mg-Al ratios for the end members dravite NaMg₃Al₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH) and Mg-foitite &ding6F;(Mg₂Al)Al₆ (Si₆O₁₈)(BO₃)₃(OH)₃(OH). Six different Na concentrations were investigated to determine the distribution of Na between tourmaline and fluid in the SiO₂-saturated system Na₂O-MgO-Al₂O₃-SiO₂-B₂O₃-H₂O-HCl. Synthetic tourmaline ranges from X-site vacant (&ding6F;) tourmaline (Mg-foitite) to nearly ideal dravite with Na=0.95 apfu. There are small, but significant, amounts of proton deficiency and negligible tetrahedral Al. Chemical variation is primarily caused by the substitutions Al&ding6F;Mg_-1Na_-1 and minor AlMg_-1H_-1. Varying amounts of Na and &ding6F; determine the Mg/Al ratios. Besides tourmaline and quartz, additional Mg-Al phases are chlorite and, at 700 °C, cordierite. Albite is also present at high Na concentrations in the bulk composition. The c dimension of the tourmaline crystals increases with Na in tourmaline. The amount of Na in the X-site depends strongly on the bulk concentration of Na in the system as well as on the temperature. These factors in turn control the phase assemblage and the composition of the fluid phase. For the assemblage tourmaline + quartz + chlorite/cordierite + fluid, a linear relationship exists between Na concentration in the fluid (quenched after the run) and tourmaline with temperature: T °C [ᆭ °C]=(Na_fluid/Na_tur)앾.878-14.692 (r²=0.96). For the assemblage tourmaline + albite + quartz + fluid, it is: T °C [ᆣ °C]=(Na_fluid/Na_tur)욝.813-6.231 (r²=0.95), where Na_fluid is the concentration of Na⁺ in the final fluid (mol/l) and Na_tur is the number of Na cations in the X-site of tourmaline. The equations are valid in the temperature range of 500-715 °C. Our experiments demonstrate that the occupancy of the X-site in combination with the changing concentrations of Al and Mg can be used to monitor changes in the fluid composition in equilibrium with a growing tourmaline crystal. Currently, this relation can be applied qualitatively to natural tourmaline to explain zoning in Na- and Al/(Al+Mg).  相似文献   

High pressure fluids in the system MgO–SiO2–H2O under upper mantle conditions     

R. Stalder  P. Ulmer  A. Thompson  D. Günther 《Contributions to Mineralogy and Petrology》2001,140(5):607-618

Fluids and melts have been trapped and analysed in high pressure experiments in the model mantle system MgO-SiO₂-H₂O at 6 to 10.5 GPa and 900 to 1,200 °C. The fluid/melt traps consisted of a diamond layer that was added to the experimental charge and was separate from the silicate phases. The recovered diamond traps were analysed by laser ablation - ICP - MS. Starting materials were synthetic mixtures of brucite, talc and silica with variable Mg/Si containing 11-31 wt% H₂O. Experiments on a serpentine starting composition [Mg₃Si₂O₅(OH)₄] result in MgO/SiO₂ weight ratios in the subsolidus fluids close to 1 at 6 GPa and close to 2 at 9 GPa. Melt compositions at 6 and 9 GPa have MgO/SiO₂ ratios close to that of forsterite. At a single pressure the amount of dissolved silicate in the fluid increases steadily with increasing temperature up to 1,150 °C, where a sudden increase of both SiO₂ and MgO is observed. This discrete step marks the solidus, which is more clearly developed at 6 than at 9 GPa. Thus, hydrous melts within the model mantle subsystem Mg₂SiO₄-Mg₂Si₂O₆-H₂O are chemically distinct from aqueous fluids up to at least 9 GPa, corresponding to 300 km depth. Extrapolation of the current data set implies that total convergence between fluid and melt along the solidus probably occurs at 12-13 GPa (~400 km), i.e. close to the Earth's mantle transition zone. Beneath cratons, interactions of hydrous fluids with upper mantle lithologies cause relative silica depletion (olivine enrichment) at depths greater than 200 km and silica (orthopyroxene) enrichment at shallower depths.  相似文献   

Peralkalinity, Al{rightleftharpoons}Si Substitution, and Solubility Mechanisms of H2O in Aluminosilicate Melts     

MYSEN  BJORN 《Journal of Petrology》1992,33(2):347-375

The solubility mechanisms of H₂O in peralkaline sodium aluminosilicatequenched melts (anhydrous NBO/T = 0.5) have been studied withRaman spectroscopy as a function of Al/(Al + Si) (0–0–3)and H²O content (0–7.5 wt.%). The coexisting structuralunits in the anhydrous quenched melts are TO2 (Q4), T2O5(Q3),and TO3 (Q2). In Al-free Na₂Si₄O₉ (NS4) melt, H₂O forms complexes with Na⁺(Na–OH bonds) and with Si⁴⁺ (Si–OH bonds). MolecularH₂O is also detected. TO3 structural units are not detectedin this composition. In the H₂O concentration range between0 and 4 wt.%, there is an approximately 20% increase in NBO/Tresulting from the increased abundance ratio, T₂O₅/TO2. Withfurther increments in water activity, the NBO/T of hydrous NS4melt is reduced. The depolymerization results from hydroxylationof the silica tetrahedra, whereas polymerization is due to formationof complexes with Na–OH bonding. In Al-bearing compositions on the Na₂Si₄O₉–Na₂(NaAl)₄O₉–join, there is evidence for Al–OH bonding in additionto Na–OH and Si–OH bonds. Among these complexes,the relative abundance of those with Si–OH bonds diminisheswith increasing Al/(A1 + Si), whereas complexes with Al–OHand Na–OH bonds become more important. Complexes withNa–OH bonds dominate for H₂O4 wt.%, whereas complexeswith Al–OH dominate at higher water content. The threestructural units, TO₃, T₂O₅, and TO², were observed in bothanhydrous and hydrous peralkaline sodium aluminosilicate melts.Their abundance varies, however, with the H₂O concentrationin the melts. The NBO/T decreases to a minimum (a 30–50%lowering of NBO/T relative to anhydrous materials) for low H₂Ocontents (3–4 wt.% H₂O), and increases as the H₂O contentis increased further.  相似文献   

Synthesis, properties and stability of end member boromuscovite, KAl2[BSi3O10](OH)2     

Ingo Jung  Werner Schreyer 《Contributions to Mineralogy and Petrology》2002,143(6):684-693

End member boromuscovite, with nearly the ideal composition, was synthesized as a single phase from mixtures of its own composition, or with excess boron and water, at high pressures of between 15 and 30 kbar at 700 °C. The mica synthesized consists of a mixture of 2M₁ and 1M polytypes with the cell dimensions of 2M₁: a=5.071(4), b=8.786(4), c=19.830(89) Å, #=95.84(12)°, V=878.5(1.4) ų; and 1M: a=5.059(5), b=8.819(6), c=10.025(17) Å, #=101.39(57)°, V=438.4(1.3) Å. The IR spectrum shows characteristic differences relative to that of muscovite. DTA registers an endothermic peak due to dehydration breakdown above 680 °C. Seeded experiments indicate that boromuscovite is a high-pressure phase requiring minimum pressures of 3 to 10 kbar at temperatures that concomitantly increase from 300 to 750 °C. At lower pressures, the anhydrous solid assemblage K-feldspar + Al-borate (probably Al₄B₂O₉) coexists with a vapor rich in boric acid. The conversion of this assemblage to boromuscovite is connected with increases in the coordination number of B from [3] to [4], and of Al from [4] to [6]. Above 10 kbar, the boromuscovite stability field is limited along its high-temperature side by congruent (or incongruent?) melting of the mica, starting near 750 °C and 10 kbar and increasing to about 900 °C at 50 kbar, although, at such very high pressures a supercritical fluid may be present. Because, even in the presence of excess-boron fluid, the synthetic mica shows invariable X-ray properties, it is concluded that one B atom per formula unit represents the maximum, and - contrary to olenitic tourmalines - no further substitution of Si by B linked with addition of hydrogen takes place. In contrast to muscovite, KAl₂[AlSi₃O₁₀](OH)₂, end member boromuscovite is not stable under normal P-T conditions of the Continental Crust along a 30 °C/km geotherm, and especially not during the intrusion of acidic igneous rocks including their pegmatites, which may explain its scarcity in nature. However, it may form in the waning hydrothermal stages of deep-seated (>10.5 km) pegmatites and - providing sufficient boron is available - in HP/LT subduction zone environments, where it may carry boron to considerable depths.  相似文献   

Kinetics of crystallization: example of micro-crystallization in basalt lava   总被引：1，自引：0，他引：1  

Dorothee J. Burkhard 《Contributions to Mineralogy and Petrology》2002,142(6):724-737

The kinetics of crystallization of basalt glass from Kilauea, Hawaii, was investigated to derive time and temperature dependence of growth rates, and to relate these results to crystallization characteristics that develop during in-place cooling of lava and isothermal re-heating in the lab. The choice of temperatures of re-heating was based on observations that pyroxene and Fe-Ti oxide production starts at about 850 °C and plagioclase above 920 °C. Crystallization parameters were determined by the crystal size distribution method (CSD), which allows one to derive growth (G) and nucleation (J) rates, if the residence time within the temperature interval of crystallization is known. For the in-place cooled lava, the residence time was determined from cooling rates that could be derived from literature data of temperature measurements in the upper 2 cm of lava lobes. Re-heating of basalt glass as a function of time shows a linear relationship between log G and log (time): % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabiabaaGcbaGaciiBaiaac+ % gacaGGNbGaam4raiabg2da9iabgkHiTiaadggaciGGSbGaai4Baiaa % cEgacaWG0bGaeyOeI0Iaam4AamaaBaaaleaacaaIXaaabeaaaaa!42ED! logG = - alogt - k₁\log G = - a\log t - k_1 . This observation was possible because the time scale of crystallization was similar to the observational time scale, a condition usually not given for cooling processes. The time dependence of G is shown to correspond to a decrease in G (and J) from the original surface-air interface to the interior of the lava: a change that occurs concomitant with an increase in crystal size and number density. Hence, it is the time dependence of G that explains the hitherto well-observed relationship with cooling rate along a temperature gradient in magmatic bodies. Moreover, the log-linear relationship between time and growth rate is suggested to describe heterogeneous nucleation and growth, which is independent of the process, i.e. cooling or metamorphism. Isothermal re-heating extinguishes the high growth rate signatures of cooling. Temperature dependence of growth rates, carried out at 24 h, shows minimum temperatures of 900-950 °C, which, because of the time dependence of growth, refers to the nucleation and crystallization maximum, and is in agreement with results from differential scanning calorimetry.  相似文献