The P-T-fO 2 stability of deerite,Fe 12 2+ Fe 6 3+ [Si12O40](OH)10     

Dominique Lattard  Nicole Le Breton 《Contributions to Mineralogy and Petrology》1994,115(4):474-487

New equilibrium experiments have been performed in the 20–27 kbar range to determine the upper thermal stability limit of endmember deerite, Fe ₁₂ ²⁺ Fe ₆ ³⁺ [Si₁₂O₄₀](OH)₁₀. In this pressure range, the maximum thermal stability limit is represented by the oxygen-conserving reaction: deerite(De)=9 ferrosilite(Fs)+3 magnetite(Mag)+3 quartz(Qtz)+5 H₂O(W) (1). Under the oxygen fugacities of the Ni-NiO buffer the breakdown-reduction reaction: De=12 Fs+2 Mag+5 W+1/2 O₂ (10) takes place at lower temperatures (e.g. T=63° at 27 kbar). The experimental brackets can be fitted using thermodynamic data for ferrosilite, magnetite and quartz from Berman (1988) and the following 1 bar, 298 K data for deerite (per gfw): V^o=55.74 J.bar^-1, S^o=1670 J.K^-1, H _f ^o =-18334 kJ, =2.5x10^-5K^-1, =-0.18x10^-5 bar^-1. Using these data in conjunction with literature data on coesite, grunerite, minnesotaite, and greenalite, the P-T stability field of endmember deerite has been calculated for P _s=P _{H 2}O. This field is limited by 6 univariant oxygenconserving dehydration curves, from which three have positive dP/dT slopes, the other three negative slopes. The lower pressure end of the stability field of endmember deerite is thus located at an invariant point at 250±70°C and 10+-1.5 kbar. Deerite rich in the endmember can thus appear only in environments with geothermal gradients lower than 10°C/km and at pressures higher than about 10 kbar, which is in agreement with 4 out of 5 independent P-T estimates for known occurrences. The presence of such deerite places good constraints on minimum pressure and maximum temperature conditions. From log f _{O 2}-T diagrams constructed with the same data base at different pressures, it appears that endmember deerite is, at temperatures near those of its upper stability limit, stable only over a narrow range of oxygen fugacities within the magnetite field. With decreasing temperatures, deerite becomes stable towards slightly higher oxygen fugacities but reaches the hematite field only at temperatures more than 200°C lower than the upper stability limit. This practically precludes the coexistence deerite-hematite with near-endmember deerite in natural environments.  相似文献   

Origin and thermal evolution of icy satellites     

Angioletta Coradini  Costanzo Federico  Olivier Forni  Gianfranco Magni 《Surveys in Geophysics》1995,16(4):533-591

The paper reviews the problem of formation and evolution of the so-called regular satellites of the giant planets, and it consists of two parts: the first describes the possible origin of the satellites, the second studies their evolution, attempting to stress the relations of the present status of the satellites with their evolutionary history.The formation of regular satellite systems around giant planets is probably related to the formation of the central planet. Some characteristics of regular satellite systems are quite similar, and suggest a common origin in a disk present around the central body. This disk can originate through different mechanisms which we will describe, paying attention to the so-called accretion disk model, in which the satellite-forming material is captured. The disk phase links the formation of the primary body with the formation of satellites. The subsequent stages of the disk's evolution can lead first to the formation of intermediate size bodies, and through the collisional evolution of these bodies, to the birth of satellite embryos able to gravitationally capture smaller bodies.Given the scenario in which icy satellites may be formed by homogeneous accretion of planetesimals made of a mixtures of ice and silicates, if no melting occurs during accretion, the satellites have a homogeneous ice-rock composition. For the smaller satellites this homogeneous structure should not be substantially modified; only sporadic local events, such as large impacts, can modify the surface structure of the smaller satellites. For the larger satellites, if some degree of melting appears during accretion, a differentiation of the silicate part occurs, the amount of differentiation and hence the core size depending on the fraction of gravitational potential energy retained during the accumulation process. Melting and differentiation soon after the accretion, for the larger satellites, could also depend on the convective evolution in presence of phase transitions and generate an intermediate rock layer, considerably denser than the underlying, still homogeneous core, and unstable to overturning on a geologic time scale. Moreover the liquid water mantle could be a transient feature because the mantle would freeze over several hundred million years. For these large bodies the stable configuration is expected to be one consisting of a silicate core and a mantle of mixed rock and ice.  相似文献   

Surface texture of Vesta from optical polarimetry     

T. Le Bertre  B. Zellner 《Icarus》1980,43(2):172-180

Polarimetric, photometric, and reflectance spectroscopic properties of asteroid 44 Vesta are simulated in the laboratory by a preparation of eucrite Bereba consisting oof a broad mixture of particle sizes (mainly greater than 50-μm) mixed and partially coated with particles of size 10 μm and less. Coarse grains are necessary for producing the same albedo and a very fine dust coating is necessary for producing the same polarization inversion angle as observed for Vesta. There are less small grains and fine dust in this sample than in lunar soils. Photometrically, if coating a sphere, this sample shows a constant brightness on the sunward half of the observed hemisphere, the brightness being given on the other half by the Minnaert reciprocity principle. With such a photometric behavior, the global geometric albedo and the sub-Earth point geometric albedo differ by no more than 5%. The microscopic phase coefficient β is 0.021 magnitude per degree for the sample; the larger value, β = 0.025, observed telescopically for Vesta indicates that large-scale roughness is present on this asteroid.  相似文献   

Corporate Organisation, Corporate Strategy and Agribusiness Development in New Zealand: An Introductory Study with Particular Reference to the Fruit and Vegetable Processing Industry     

R. B. Le Heron  E. C. R. Warr 《New Zealand geographer》1976,32(1):1-16

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煤炭城市生态环境可持续发展研究--以淮南市为例     

邢琴琴  焦华富  尹乐 《世界地理研究》2006,15(2):54-60

根据城市生态学原理和方法,针对煤炭城市生态环境特点,构建了能够体现煤炭城市生态环境质量主要特征的,定性、定量考核的评价指标体系。利用层次分析、变权综合指数等方法,建立了煤炭城市生态环境质量综合评价模型。从自然、经济、社会三个方面对淮南市生态环境质量进行评价,并对淮南市生态环境可持续发展提出了相应对策。  相似文献   

Mean flow-transient perturbation interaction in the Southern Hemisphere: a simulation using a variable-resolution GCM     

A. Carril  C. Menéndez  M. Nuñez  H. Le Treut 《Climate Dynamics》2002,18(8):661-673

The ability of an atmospheric general circulation model to reproduce fundamental features of the wintertime extratropical Southern Hemisphere (SH) circulation is evaluated with emphasis on the daily variability of the SH mean flow and the mean flow-transient perturbations interaction. Two 10-year simulations using a new version of the LMDZ GCM with a stretched grid scheme centered at 45 °S and forced by climatological SST are performed: a high (144Ꮡ) and low (64Ꭹ) horizontal resolution runs. The performance of both simulations was determined by comparing several simulated fields (zonal wind, temperature, kinetic energy, transient eddy momentum and heat fluxes, Eliassen-Palm fluxes, Eady growth rate and baroclinic conversion term) against the European Centre for Medium Range Weather Forecast reanalyses (ERA). High and low-resolution simulations are similar in many respects; in particular, both experiments reproduce the main patterns of the southern extratropical large-scale circulation satisfactorily. Increasing resolution does not improve universally some spurious aspects of the low resolution simulation (e.g. the cold bias in the high polar troposphere, the debilitated subtropical jet, the low baroclinic conversion rate). Those aspects present little sensitivity to the model resolution. The interaction between transient eddies and zonal mean flow are examined. The low-resolution experiment is able to qualitatively represent the acceleration/deceleration of the mean flow by transient perturbations, south/north of 30 °S with an accuracy similar to that of the high-resolution experiment. Although both experiments represent the baroclinic structure of the mean flow satisfactorily, the model underestimates some transient properties due to the underestimation of the baroclinic conversion term in middle latitudes. Such misrepresentation does not improve with increasing resolution and is related to the relatively weak meridional temperature gradient and the inadequate geographical distribution of the eddy heat fluxes. In particular, the eddy kinetic energy is always underestimated. Eddy kinetic energy does not improve convincingly with increasing resolution, suggesting that the adequate representation of the storm tracks is highly influenced by the physical parametrizations.  相似文献   

A thermodynamic model for Fe–Mg dioctahedral K white micas using data from phase-equilibrium experiments and natural pelitic assemblages     

Teddy Parra  Olivier Vidal  Phillipe Agard 《Contributions to Mineralogy and Petrology》2002,143(6):706-732

The purpose of this study is to derive a solid-solution model for potassic white micas (KWM) encountered in rocks of various bulk compositions, over a wide range of P-T conditions. A compilation of phengite compositions lead us to propose a seven-thermodynamic-component (muscovite, Fe²⁺-Al-celadonite, Mg-Al-celadonite, annite, phlogopite, pyrophyllite and paragonite) ionic solid-solution model which accounts for the Tschermak, Fe-Mg, di/trioctahedral, pyrophyllitic and paragonitic substitutions observed in nature. A four-site mixing model with symmetric Margules parameters to model the Tschermak substitutions, asymmetric Margules parameters to model the other substitutions, and ideal intersite interaction has been adopted. In contrast to previous models, the relevant thermodynamic data and solid-solution properties are calibrated with independent sets of published experiments conducted for the KMASH, KFASH, KFMASH, and KNASH systems, as well as about 200 natural data involving KWM assemblages. The constraints span a wide range of pressure and temperature conditions (150 to 750 °C, 0.5 to 30 kbar), so that our model does not need to be extrapolated outside the calibration range to be used for P-T thermobarometric purposes. The calculated thermodynamic data are interconsistent with the TWQ thermodynamic database and solid-solution models, including that recently published for chlorites.  相似文献   

Morphology, origin and infrared microthermometry of fluid inclusions in pyrite from the Radka epithermal copper deposit, Srednogorie zone, Bulgaria   总被引：3，自引：0，他引：3  

Kalin Kouzmanov  Laurent Bailly  Claire Ramboz  Olivier Rouer  Jean-Michel Bény 《Mineralium Deposita》2002,37(6-7):599-613

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Up to what temperature is petroleum stable? New insights from a 5200 free radical reactions model     

Florent Domin  Roda Bounaceur  Gerard Scacchi  Paul-Marie Marquaire  Daniel Dessort  Bernard Pradier  Olivier Brevart 《Organic Geochemistry》2002,33(12)

The discovery of crude oils and condensates at ever higher temperatures casts doubt on the validity of the usual geochemical modelling approach, that uses empirical reactions and rate constants. The solution used to account for such a high thermal stability is presently to adjust the rate parameters, but the physical meaning and scientific value of such a strategy can be questioned. We have developed a mechanistic model consisting of 5200 lumped free radical reactions to describe the thermal evolution of a mixture of 52 organic species meant to represent light petroleum. Rate constants used are those available in the literature or estimated using well established thermochemistry-reactivity correlations. Chemical structures included in the model are linear, branched and cyclic hydrocarbons, hydro- and alkyl-aromatics, PAHs, and three heteroatomic compounds. Reactions include cracking and alkylation chains and inhibiting and accelerating reactions from the various reactants. This model has been applied to several mixtures with various proportions of reaction inhibitors and accelerators, and to a composition representing a light mature oil. From the results obtained, we conclude that mature oils will be stable up to 240–260 °C, depending on their composition, and that the thermal cracking of oil to gas is not possible under reasonable basin conditions. The kinetics of petroleum cracking are thus much slower than generally recognized.  相似文献   

Book review: L'écologie urbaine et l'urbanisme. Aux fondements des enjeux actuels     

Vincent Berdoulay  Olivier Soubeyran 《GeoJournal》2002,57(4):346-347

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