Thermodynamics of plagioclase III: Spontaneous strain at the I\overline 1 - P\overline 1 phase transition in Ca-rich plagioclase     

Simon A. T. Redfern  Ann Graeme-Barber  Ekhard Salje 《Physics and Chemistry of Minerals》1988,16(2):157-163

The lattice parameters of anorthites An₉₈Ab₂ and An₁₀₀ have been measured from 22 to 1100 K. The spontaneous strain arising from the \(I\overline 1 - P\overline 1\) displacive transition in An₉₈ follows second order Landau behaviour. The spontaneous strain (? _s) couples quadratically to the order parameter (Q ⁰) with ? _s∝Q ⁰²∝(T _c ^* ?T) and T _c ^* =530 K in An₉₈. This is in contrast to the tricritical behaviour observed in pure anorthite. These observations are consistent with a Landau model for the free energy of Ca-rich plagioclases in which Al/Si order and Na content renormalize the fourth order coefficient.  相似文献   

Equilibrium thermodynamics of Al/Si ordering in anorthite     

M. A. Carpenter 《Physics and Chemistry of Minerals》1992,19(1):1-24

Variations in the equilibrium degree of Al/Si order in anorthite have been investigated experimentally over the temperature range 800-1535° C. Spontaneous strain measurements give the temperature dependence of the macroscopic order parameter, Q, defined with respect to the \(C\bar 1 \rightleftharpoons I\bar 1\) phase transition, while high temperature solution calorimetric data allow the relationship between Q and excess enthalpy, H, to be determined. The thermodynamic behaviour can be described by a Landau expansion in one order parameter if the transition is first order in character, with an equilibrium transition temperature, T _tr, of ～2595 K and a jump in Q from 0 to ～0.65 at T_tr. The coefficients in this Landau expansion have been allowed to vary with composition, using Q=1 at 0 K for pure anorthite as a reference point for the order parameter. Published data for H and Q at different compositions allow the calibration of the additional parameters such that the free energy due to the \(C\bar 1 \rightleftharpoons I\bar 1\) transition in anorthite-rich plagioclase feldspars may be expressed (in cal. mole^-1) as: \(\begin{gathered}G = \tfrac{1}{2} \cdot 9(T - 2283 + 2525X_{Ab} )Q^2 \\ {\text{ + }}\tfrac{1}{4}( - 26642 + 121100X_{Ab} )Q^4 \\ {\text{ + }}\tfrac{1}{6}(47395 - 98663X_{Ab} )Q^6 \\ \end{gathered}\) where X _Ab is the mole fraction of albite component. The nature of the transition changes from first order in pure anorthite through tricritical at ～An₇₈ to second order, with increasing albite content. The magnitude of the free energy of \()\) ordering reduces markedly as X _Ab increases. At ～700° C incommensurate ordering in crystals with compositions ～An₅₀–An₇₀ needs to have an associated free energy reduction of only a few hundred calories to provide a more stable structure. These results, together with a simple mixing model for the disordered ( \()\) ) solid solution, an assumed tricritical model for the incommensurate ordering and published data for ordering in albite have been used to calculate a set of possible free energy relations for the plagioclase system. The incommensurate structure should appear on the equilibrium phase diagram, but its apparent stability with respect to the assemblage albite plus anorthite at low temperatures depends on the values assigned to the mixing parameters of the $$$$ solid solution.  相似文献   

Thermodynamics of plagioclase II: Temperature evolution of the spontaneous strain at the I\bar 1 \leftrightarrow P\bar 1 phase transition in anorthite     

Simon A. T. Redfern  Ekhard Salje 《Physics and Chemistry of Minerals》1987,14(2):189-195

The temperature dependence of the lattice parameters of pure anorthite with high Al/Si order reveals the predicted tricritical behaviour of the \(I\bar 1 \leftrightarrow P\bar 1\) phase transition at T _c ^* =510 K. The spontaneous strain couples to the order parameter Q° as x _i∝S _xQ ⁱ Q°² with S _xQ ¹ =4.166×10^?3, S _xQ ² =0.771×10^?3, S _xQ ³ =?7.223×10^?3 for the diagonal elements. The temperature dependence of Q° is $$Q^{\text{o}} = \left( {1 - \frac{T}{{510}}} \right)^\beta ,{\text{ }}\beta = \tfrac{{\text{1}}}{{\text{4}}}$$ A strong dependence of T _c ^* , S _xQ ⁱ and β is predicted for Al/Si disordered anorthite.  相似文献   

Optical absorption spectra of iron ions in vivianite     

M. N. Taran  A. N. Platonov 《Physics and Chemistry of Minerals》1988,16(3):304-310

Absorption bands are determined in polarized optical spectra of vivianite Fe₃(PO₄)₂·8H₂O, recorded at room and low temperatures. These bands are caused by spin-allowed d-d transitions in structurally nonequivalent Fe _A ²⁺ (～11000 cm^-1 (γ-polarization) (and) ～12000 cm^-1 (β-polarization)) (and) Fe _B ²⁺ (～8400 cm^-1 (γ, α-polarization) and ～11200 cm^-1 (α-polarization)) ions. A charge transfer band (CTB) Fe _B ²⁺ +Fe _B ³⁺ →Fe _B ²⁺ +Fe _B ²⁺ (～15000 cm^-1) also determined, has polarizing features giving evidence of a change in the Fe _B ²⁺ -Fe _B ³⁺ bond direction, when compared with Fe _B ²⁺ -Fe _B ²⁺ . Bands of exchange-coupled Fe³⁺-Fe³⁺ pairs (～19400, ～20400, ～21300 and ～21700 cm^-1) which appear on oxidation of Fe²⁺ in paired Fe _B octahedra are also characterized.  相似文献   

Interdiffusion of NaSi—CaAl in peristerite     

Richard A. Yund 《Physics and Chemistry of Minerals》1986,13(1):11-16

The ‘average’ interdiffusion coefficient ( \(\bar D\) ) for NaSi—CaAl exchange in plagioclase for the interval from An₀ to An₂₆ was estimated from experimentally determined homogenization times for peristerite exsolution lamellae. The average spacing between adjacent (unlike) lamellae is 554±77 Å. Dry heating in air at 1,100°C for 98 days produced no change in the exsolution microstructure; thus \(\bar D\) (dry)<10^?17 cm²/s. This limit is consistent with the recently reported ‘average’ \(\bar D\) (dry) values for the Huttenlocher interval (An_70–90) at this temperature. At 1.5 GPa with about 0.2 weight percent water added the ‘average’ diffusion coefficient from 1,100°C to 900°C is given by: \(\bar D\) (wet)=18 _?15 ⁺¹⁰⁸ (cm²/s) exp (?97±5 (kcal/mol)/RT), where R is the gas constant, and T is °K. This \(\bar D\) (wet) at 1,100°C is more than three orders of magnitude greater than \(\bar D\) (dry) for Na- and Ca-rich plagioclases.  相似文献   

Experimental delineation of the “e” ⇌ I\bar 1 and “e” ⇌ C\bar 1 transformations in intermediate plagioclase feldspars     

Michael A. Carpenter 《Physics and Chemistry of Minerals》1986,13(2):119-139

Approximately 125 hydrothermal annealing experiments have been carried out in an attempt to bracket the stability fields of different ordered structures within the plagioclase feldspar solid solution. Natural crystals were used for the experiments and were subjected to temperatures of ～650°C to ～1,000°C for times of up to 370 days at \(P_{{\text{H}}_{\text{2}} {\text{O}}} \) =600 bars, or \(P_{{\text{H}}_{\text{2}} {\text{O}}} \) =1,200 bars. The structural states of both parent and product materials were characterised by electron diffraction, with special attention being paid to the nature of type e and type b reflections (at h+k=(2n+1), l=(2n+1) positions). Structural changes of the type C \(\bar 1\) → I \(\bar 1\) , C \(\bar 1\) → “e” structure, I \(\bar 1\) → “e” and “e” structure → I \(\bar 1\) have been followed. There are marked differences between the ordering behaviour of crystals with compositions on either side of the C \(\bar 1\) ? I \(\bar 1\) transition line. In the composition range ～ An₅₀ to ～ An₇₀ the e structure appears to have a true field of stability relative to I \(\bar 1\) ordering, and a transformation of the type I \(\bar 1\) ? e has been reversed. It is suggested that the e structure is the more stable ordered state at temperatures of ～ 800°C and below. For compositions more albite-rich than ～ An₅₀ the upper temperature limit for long range e ordering is lower than ～ 750°C, and there is no evidence for any I \(\bar 1\) ordering. The evidence for a true stability field for “e” plagioclase, which is also consistent with calorimetric data, necessitates reanalysis both of the ordering behaviour of plagioclase crystals in nature and of the equilibrium phase diagram for the albite-anorthite system. Igneous crystals with compositions of ～ An₆₅, for example, probably follow a sequence of structural states C \(\bar 1\) → I \(\bar 1\) → e during cooling. The peristerite, Bøggild and Huttenlocher miscibility gaps are clearly associated with breaks in the albite, e and I \(\bar 1\) ordering behaviour but their exact topologies will depend on the thermodynamic character of the order/disorder transformations.  相似文献   

The thermodynamics of the I \overline{1} –P \overline{1} phase transition in Ca-rich plagioclase from an assessment of the spontaneous strain     

Mario Tribaudino  Ross J. Angel 《Physics and Chemistry of Minerals》2012,39(9):699-712

In-situ powder diffraction measurements between 90 and 935?K on four anorthite-rich plagioclase samples (An₁₀₀, An₉₆Ab₄, An₈₉Ab₁₁ and An₇₈Ab₂₂) were used to determine the detailed evolution of these samples through the $I \overline{1} $ – $P \overline{1} $ phase transition. The c-type reflections indicative of $P \overline{1} $ symmetry were detected only in An₁₀₀, An₉₆Ab₄, whereas deviations in the evolution of the unit-cell parameters with temperature were observed in all samples, most prominently in the β unit-cell angle. The c-type reflections disappear at ~510 and ~425?K in An₁₀₀ and An₉₆Ab₄ respectively, and their intensity decreases according to a tricritical trend $ I^{2} \propto \left( {T - T_{\text{c}} } \right) $ . The cell parameter changes were used to determine the spontaneous strains arising from the transition which were modelled with Landau theory, allowing for low-temperature quantum saturation, in order to determine the thermodynamic behaviour. In An₁₀₀ tricritical behaviour was observed [T _c?=?512.7(4)?K; θ_s?=?394(4)] in good agreement with previous studies, and the c-type superlattice reflections indicative of $P \overline{1} $ symmetry persist up to the T _c determined from the spontaneous strain, and then disappear. The evolution of the spontaneous strain in An₉₆Ab₄ is tricritical at low temperatures [T _c?=?459(1) K, θ_s?=?396(5)] up to the temperature of disappearance of c-type reflections, but becomes second order beyond ~440?K. In An₈₉Ab₁₁ the strain displays second-order behaviour throughout [T _c?=?500(1) and θ_s?=?212(5)], and the c-type reflections are not detected in the powder diffraction patterns at any temperature. The apparent discrepancy between the absence of c-type reflections in temperature ranges where the cell parameters display significant spontaneous strain is resolved through consideration of the sizes of the anti-phase domains within the crystals. It is deduced that the tricritical phase transition occurs in well-ordered crystals with large domains in which the behavior of individual domains is dominant (i.e. in pure anorthite) or where the $P \overline{1} $ distortions within the domains are large enough to dominate the structural coherency strains between the domains. When both the magnitude of the $P \overline{1} $ pattern of displacements of the tetrahedral framework become smaller and the influence of the structural coherency between anti-phase domains becomes significant, the thermodynamic behavior becomes 2nd-order in character, the c-type reflections disappear, and the orientation of the spontaneous strain changes.  相似文献   

Gehlenite stability in the system CaO-Al2O3-SiO2-H2O-CO2     

Gert Hoschek 《Contributions to Mineralogy and Petrology》1974,47(4):245-254

P, T, \(X_{{\text{CO}}_{\text{2}} }\) relations of gehlenite, anorthite, grossularite, wollastonite, corundum and calcite have been determined experimentally at P _f =1 and 4 kb. Using synthetic starting minerals the following reactions have been demonstrated reversibly

1. 2 anorthite+3 calcite=gehlenite+grossularite+3 CO₂.
2. anorthite+corundum+3 calcite=2 gehlenite+3 CO₂.
3. 3anorthite+3 calcite=2 grossularite+corundum+3CO₂.
4. grossularite+2 corundum+3 calcite=3 gehlenite+3 CO₂.
5. anorthite+2 calcite=gehlenite+wollastonite+2CO₂.
6. anorthite+wollastonite+calcite=grossularite+CO₂.
7. grossularite+calcite=gehlenite+2 wollastonite+CO₂.

In the T, \(X_{{\text{CO}}_{\text{2}} }\) diagram at P _f =1 kb two isobaric invariant points have been located at 770±10°C, \(X_{{\text{CO}}_{\text{2}} }\) =0.27 and at 840±10°C, \(X_{{\text{CO}}_{\text{2}} }\) =0.55. Formation of gehlenite from low temperature assemblages according to (4) and (2) takes place at 1 kb and 715–855° C, \(X_{{\text{CO}}_{\text{2}} }\) =0.1–1.0. In agreement with experimental results the formation of gehlenite in natural metamorphic rocks is restricted to shallow, high temperature contact aureoles.  相似文献   

Hydrotalcite-like solid solutions with variable SO 4 2− and CO 3 2− contents at 50° C     

Carole Le Bail  Jean-Hugues Thomassin  Jean-Claude Touray 《Physics and Chemistry of Minerals》1987,14(4):377-382

Hydrotalcite-like solid solutions have been synthesized by coprecipitation in basic solutions with variable SO ₄ ^2? /CO ₃ ^2? ratios. Chemical determination of CO ₃ ^2? in the interlayer was impossible because of the presence of minor hydromagnesite. SO ₄ ^2? was determined both by chemical analysis and X-ray photoelectron spectroscopy (XPS), the two methods giving similar results. A Raman spectrometry gave additional data on the SO ₄ ^2? /CO ₃ ^2? ratio. Then, the stoichiometry of the anionic interlayers, X _s , X _c , and X _OH were determined, and the influence of X _s on the c′ parameter (increasing from c′=7.97 Å to c′=8.63 Å between X _s =0 and X _s =1) was characterized. In addition, a partitioning curve of SO ₄ ^2? and CO ₃ ^2? between aqueous solutions and hydrotalcite-like compounds was established. Its general shape strongly suggests a miscibility gap between a sulfate-rich end and a carbonate-rich solid solution (maximum SO ₄ ^2? /CO ₃ ^2? about 0.2). This result explains why most of the hydrotalcites synthesized during experimental alteration of basaltic glasses by sea-water (a sulfate-rich solution) are CO ₃ ^2? -rich solid solutions.  相似文献   

A dynamical model for the I\bar 1 - P\bar 1 phase transition in anorthite,CaAl2Si2O8     

Dorian M. Hatch  Subrata Ghose 《Physics and Chemistry of Minerals》1989,16(6):614-620

The non-ferroic triclinic to triclinic \(I\bar 1 - P\bar 1\) phase transition in anorthite is described in terms of the spontaneous onset of an order parameter η. A triclinic to triclinic phase transition can be driven by order parameters (representations) arising from the Γ, Z, X, U, V, R, Y, and T points of symmetry of the Brillouin zone. Each point leads to a set of two inequivalent representations and thus there is a total of sixteen inequivalent order parameters. However, only the R ₁ ⁺ representation is consistent with the change from the body-centered to primitive cell (increase of primitive cell size of two) and also with the origin of the two space groups (inversion center) being at the same position. The R ₁ ⁺ order parameter of the high symmetry triclinic phase \(P\bar 1_0\) (or equivalently \(I\bar 1\) ) causes a reciprocal lattice change and, in terms of the lower symmetry reciprocal lattice, the order parameter corresponds to the b^* point. This is consistent with experimentally observed x-ray diffuse scattering. Using induced representation theory, microscopic distortions compatible with the R ₁ ⁺ order parameter are obtained. Assuming a distortion in an arbitrary direction at the general 2(i) Wyckoff position (x₀,y₀,z₀) of \(P\bar 1_0\) (the higher symmetry phase) induced representation theory demands an opposite displacement at the position (x₀, y₀, z₀), an opposite displacement at (x₀+1,y₀+1,z₀+1), and the same displacement at ( \(\bar x\) ₀+1, \(\bar y\) ₀+1, \(\bar z\) ₀+1) of \(P\bar 1_0\) . This is also consistent with experiment. The presence of the weak c-type reflections above the transition is attributed to the fluctuating lower symmetry antiphase domains related by the translation (1/2, 1/2, 1/2).  相似文献   

A theoretical study of bond distances,X-ray spectra and electron density distributions in borate polyhedra     

Abha Gupta  J. A. Tossell 《Physics and Chemistry of Minerals》1981,7(4):159-164

The borate polyhedra BO ₃ ^3? , B(OH)₃, BO ₄ ^5? , and B(OH) ₄ ^? are studied using the ab initio and multiple scattering Xα quantum mechanical methods. The ab initio self-consistent-field (SCF) molecular orbital (MO) method, at the minimum basis set level, predicts equilibrium B-O distances within 0.04 Å of their average values in solids so long as the polyhedron charge is small. Orbital energies from double zeta basis set ab initio calculations and analogies with isoelectric compounds are used to assign the X-ray spectra of BO ₃ ^3? and to predict the valence region spectra of BO ₄ ^5? . Contour maps of the difference between molecular and superimposed free atom electron densities show charge buildup along the B-O bond which is only slightly smaller than that observed in CO ₃ ^2? .  相似文献   

On the nonstoichiometry and point defects of olivine     

A. Nakamura  H. Schmalzried 《Physics and Chemistry of Minerals》1983,10(1):27-37

This paper presents the point-defect thermodynamics for fayalite and olivine solid solutions (Fe _x Mg_1?x )₂SiO₄. By means of thermogravimetry, the metal-to-oxygen ratio of these silicates has been determined as a function of oxygen potential, compositionx and temperature. Experiments were performed in the range of 1,000° C≦T≦1,280° C and 0.2≦x≦1.0. It is found that V _Me ^″ , Fe _Me ^· and the associate {Fe′ _Si ^′ Fe _Me ^· } are the majority defects. With this knowledge it is possible to calculate the nonstoichiometry at given temperature as a function of \(p_{O_2 } \) and \(a_{SiO_2 } \) . The cation vacancy concentration shows a \(p_{O_2 }^{1/5} \) -dependence (forx≧0.2) and increases at givenT and \(p_{O_2 } \) almost exponentially with compositionx. In the composition range studied here, the silicates show an oxygen excess, and FeO is more soluble in the olivine than SiO₂.  相似文献   

Thermodynamic behaviour of the high-temperature P\bar 1{\text{-}}I\bar 1 phase transition along the CaAl2Si2O8–SrAl2Si2O8 join     

M. Tribaudino  P. Benna  F. Nestola  C. Meneghini  E. Bruno 《Physics and Chemistry of Minerals》2005,32(4):314-321

In situ high-temperature synchrotron radiation powder diffraction patterns were taken from room temperature to T = 740°C from synthetic feldspars along the join CaAl₂Si₂O₈–SrAl₂Si₂O₈ (An–SrF). Three samples of composition An₉₅SrF₅, An₉₀SrF₁₀ and An₈₅SrF₁₅ were investigated, and the evolution of cell parameters with T was determined by Rietveld analysis of powder X-ray diffraction patterns. The high-temperature $P\bar 1{\text{-}}I\bar 1$ phase transition, previously observed with T _c = 241°C in anorthite, was found in An₉₅SrF₅, An₉₀SrF₁₀ and An₈₅SrF₁₅ feldspars at T _c = 233(5)°, 195(2)° and 174(2)°C respectively. The transition was revealed by the disappearance of critical reflections and variations in the rate of change of cell parameters with temperature. A significant, although small (between 0.0025 and 0.0012 at room temperature), spontaneous strain could be measured, allowing the thermodynamic behaviour of the transition to be modelled. A second-order trend for An₉₀SrF₁₀ and An₈₅SrF₁₅ [β = 0.504(7) and 0.505(7) respectively] or nearly second-order for An₉₅SrF₅[β = 0.458(4)] was observed in contrast with tricritical behaviour of end member anorthite. An extrapolation of the T _c versus composition to room temperature indicates that the critical composition for the $P\bar 1$ phase is An₆₀SrF₄₀.  相似文献   

Urban land-use effects on groundwater phosphate distribution in a shallow aquifer, Nanfei River basin, China   总被引：1，自引：0，他引：1  

Jiazhong Qian  Lulu Wang  Hongbin Zhan  Zhou Chen 《Hydrogeology Journal》2011,19(7):1431-1442

Groundwater, surface water, soil and river sediment samples, and information on land use in the Nanfei River basin (NRB) of China have been analyzed to study the geochemistry, distribution, and mobilization of phosphorus. The distribution of phosphate (PO ₄ ^3??/sup> ) and the relationships between PO ₄ ^3??/sup> and several constituents in groundwater were studied. Partial correlation analysis relating PO ₄ ^3??/sup> to types of land use was conducted using the data analyzing tool SPSS 15.0. The processes controlling the transport of PO ₄ ^3??/sup> are discussed. The conclusions from this study are: (1) urban land use has obvious impact on PO ₄ ^3??/sup> in groundwater, the average concentration of PO ₄ ^3??/sup> being 4.37?mg/L, greater than that resulting from farmland and mixed land use, which have average PO ₄ ^3??/sup> concentrations of 0.10 and 0.18?mg/L, respectively; (2) the partial correlation between PO ₄ ^3??/sup> and types of land use is significant with a coefficient of 0.760; (3) the PO ₄ ^3??/sup> concentrations in surface water are generally higher than those in groundwater, and the total phosphorus (TP) concentrations in river sediments are generally higher than those in soil samples; (4) groundwater is a carrier of PO ₄ ^3??/sup> and is likely responsible for the redistribution of PO ₄ ^3??/sup> in different regions of NRB.  相似文献   

On the least-squares fit of small and great circles to spherically projected orientation data     

Norman H. Gray  Peter A. Geiser  James R. Geiser 《Mathematical Geosciences》1980,12(3):173-184

Given the direction cosines a _i ^′ = (a ₁ ⁱ , a ₂ ⁱ , a ₃ ⁱ )corresponding to a set of pspherically projected fabric poles, an initial estimate x′ = (x₁, x₂, x₃, x₄)for the angular radius x₄,and direction cosines of the center of the least-squares small circle which minimizes the sum of the squares of the angular residuals $$r = \sum\limits_p {\left[ {x_4 - \cos ^{ - 1} \left( {a_1^i x_1 + a_2^i x_2 + a_3^i x_3 } \right)} \right]} ^2 $$ can be iteratively improved by taking x_j+1 = x_j + Δxwhere x_j is the value of xat the jth iteration and $$\Delta x = - H_j^{ - 1} \left[ {q_j + x_j \left( {x'_j H_j^{ - 1} x_j } \right)\left( {q_j - x'_j H_j^{ - 1} q_j } \right)} \right],$$ where As an initial approximation for xwe have found it convenient to ignore the fact that the data are constrained to lie on the surface of the reference sphere and to use the parameters of a least-squares plane through the given poles. Generalization of this approach to fitting variously constrained great and small circles is easily made. The relative merits of differently constrained fits to the same data can be tested approximately if it is assumed that the errors in the location of the poles are isotropic and normally distributed. It is thus possible to statistically assess the relative significance of conflicting structural models which predict different geometrical patterns of fabric elements.  相似文献   

Standing stock and estimated production rates of phytoplankton and zooplankton in Narragansett Bay,Rhode Island     

A. G. Durbin  E. G. Durbin 《Estuaries and Coasts》1981,4(1):24-41

Seasonal changes in phytoplankton biomass and production, total zooplankton biomass, and biomass and potential production rates of the two dominant copepods, Acartia hudsonica (formerly called Acartia clausi) and Acartia tonsa are described for several stations in Narragansett Bay, R.I. Plankton in the bay behaved as a single population with simultaneous changes occurring at the upper bay (Station 5) and the lower bay (Station 1). Phytoplankton biomass was higher in the upper bay ( \(\bar x\) =16.95 mg chl a·m^?3) than in the lower bay ( \(\bar x\) =6.37 mg chl a·m^?3) and these 0269 0101 V differences in biomass were reflected in the phytoplankton production rates. The zooplankton, which was dominated by A. hudsonica in the spring and early summer and A. tonsa during summer and fall, showed no such consistent differences between the stations. Mean A. hudsonica biomass (St 1, \(\bar x\) ;=82.7 mg dry wt·m^?3; St 5, _ \(\bar x\) ;=95.2 mg dry wt·m^?3) exceeded that of A. tonsa (St 1, \(\bar x\) ;=56.7 mg dry wt·m^?3; St 5, \(\bar x\) ;=60.0 mg dry wt·m^?3). Potential production rates of the two Acartia 0269 0101 V spp. were strongly temperature dependent. Despite the higher biomass levels of A. hudsonica, low temperatures resulted in lower potential production rates ( \(\bar x\) ; St 1=7.25 mg C·m^?3 day^?1; \(\bar x\) ; St 5=10.77mg C·m^?3 day^?1) and biomass doubling times of up to 9.6 days. Potential production rates of A. tonsa at summer temperatures were high ( \(\bar x\) ; St 1=19.0 mg C·m^?3 day^?1; \(\bar x\) ; St 5=22.9 mg C·m^?3 day^?1) and biomass doubling times were generally less than one day.  相似文献   

Le gisement de tungstène de Xihuashan (Sud-Jiangxi,Chine): Relations granites,altérations deutériques-hydrothermales,minéralisations     

G. Giuliani 《Mineralium Deposita》1985,20(2):107-115

The Xihuashan tungsten deposit (South Jiangxi, China) is located on the border of a granitic stock composed of four intrusive units: γ _inf2a ^sup5 , γ _inf2b ^sup5 , γ _inf2c ^sup5 and γ _inf2e ^sup5 chronologically. The deposit is situated in γ _inf2a ^sup5 and γ _inf2b ^sup5 whose contact zone is marked by a stockscheider and by a sporadic fine-grained granite designated γ _inf2b′ ^sup5 . The feldspathic episyenitic veins or masses located mainly in γ _inf2b ^sup5 resulted from granite alteration. This alteration characterizes the fluid activity which followed previous mechanical action, remnant liquids draining under structural control. The quartz-bearing Xihuashan veins (Dayu mining district) are a typical wolframite-quartz vein deposit and have developed mainly in γ _inf2b ^sup5 . The density of the veins and the huge mineralizations in γ _inf2b ^sup5 can be explained by the carapace role played by γ _inf2a ^sup5 , γ _inf2b′ ^sup5 and the stockscheider. The deposit is formed by 615 economically valuable veins (medium grade: 1,08% in WO₃) characterized by four stages of mineralization; a reverse vertical zoning is generally observed. Thus, the Xihuashan tungsten deposit possesses a metallogenic value contributing to the comprehension of metallogenic and structural phenomena related to the evolution of granitic masses.  相似文献   

X-ray diffraction study of the orientational order/disorder transition in NaNO3: Evidence for order parameter coupling     

Wolfgang Wilhelm Schmahl  Ekhard Salje 《Physics and Chemistry of Minerals》1989,16(8):790-798

The orientational ordering transition R \(R\bar 3m - R\bar 3c\) in NaNO₃ near 552 K has been investigated using x-ray diffraction techniques. NaNO₃ is a model system for CaCO₃ and other minerals with orientational disorder of triangular molecules in a simple NaCl-type matrix. The temperature evolution of the integrated intensities of the superlattice reflection \(\bar 1\) 23 and the fundamental reflection 110 are discussed in terms of Landau theory of two coupled order parameters. It is shown that the known phenomenological critical exponent (Poon and Salje 1988) and the anomalous thermal expansion at T > T _tr (Reeder et al. 1988) can be understood as the result of a Z point instability which mainly describes the NO ₃ ^- disorder, and a second order parameter linked with the spontaneous strain of this phase transition.  相似文献   

First principles quantum mechanical calculation of the electric dipole polarizabilities of the borate,carbonate, nitrate and related ions     

J. A. Tossell 《Physics and Chemistry of Minerals》1990,17(2):133-141

Electric dipole polarizabilities have been calculated from first principles of quantum mechanics for the BO ₃ ^3? , CO ₃ ^2? , NO ₃ ^? series and for NO ₂ ^? and LiNO₃(g). Calculated trends in average polarizability and polarizability anisotropy in the BO ₃ ^3? -NO ₃ ^? series are in agreement with experiment and can be qualitatively interpreted in terms of the varying energies of the a₁′, a₂″ and e′ symmetry unoccupied MO's of the oxyanions. Embedding a CO ₃ ^2? ion in a D_3h symmetry array of divalent cations reduces both the average polarizability and its anisotropy, particularly when diffuse s and p functions are included in the calculation. Calculations on the gas phase LiNO₃ molecule and on the free NO ₃ ^? ion in the distorted geometry found in LiNO₃(g) allow us to separate polarizability contributions internal to the NO ₃ ^? and Li⁺ ions from those which arise from the Li⁺-NO ₃ ^? interaction. The Li⁺-NO ₃ ^? interaction term so obtained is much smaller than the NO ₃ ^? contribution but is in turn larger than the Li⁺ contribution, suggesting that the inclusion of this interaction term is essential for obtaining accurate results for ion pairs. Although static polarizabilities are in reasonable agreement with experiment for NO ₃ ^? the wavelength dispersion of the polarizability is underestimated by about a factor of two, apparently as a result of inadequacies in the quantum mechanical method. Calculated values are also presented for ¹⁴N NMR shieldings in the nitrogen oxyanions but these are in only qualitative agreement with the experimental values. Similarly, calculated values of magnetic susceptibility are in only qualitative agreement with experiment although trends along the BO ₃ ^3? -NO ₃ ^? series are properly reproduced.  相似文献   

A note on the significance of the assemblage calcite-quartz-plagioclase-paragonite-graphite     

E. D. Ghent  J. W. Jones  J. Nicholls 《Contributions to Mineralogy and Petrology》1970,28(2):112-116

The biotite zone assemblage: calcite-quartz-plagioclase (An₂₅)-phengite-paragonite-chlorite-graphite, is developed at the contact between a carbonate and a pelite from British Columbia. Thermochemical data for the equilibrium paragonite+calcite+2 quartz=albite+ anorthite+CO₂+H₂O yields: $$\log f{\text{H}}_{\text{2}} {\text{O}} + \log f{\text{CO}}_{\text{2}} = 5.76 + 0.117 \times 10^{ - 3} (P - 1)$$ for a temperature of 700°K and a plagioclase composition of An₂₅. By combining this equation with equations describing equilibria between graphite and gas species in the system C-H-O, the following partial pressures: \(P{\text{H}}_2 {\text{O}} = 2572{\text{b, }}P{\text{CO}}_2 = 3162{\text{b, }}P{\text{H}}_2 = 2.5{\text{b, }}P{\text{CH}}_4 = 52.5{\text{b, }}P{\text{CO}} = 11.0{\text{b}}\) are obtained for \(f{\text{O}}_2 = 10^{ - 26}\) . If total pressure equals fluid pressure, then the total pressure during metamorphism was approximately 6 kb. The total fluid pressure calculated is extremely sensitive to the value of \(f{\text{O}}_2\) chosen.  相似文献