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1.
钙铁辉石-钠长石-石英和透辉石-钠长石-石英体系的实验数据能够计算钙铁辉石-硬玉和透辉石-硬玉固溶体中硬玉的剩余自由能,如后面所示,实验点的最好近似值是根据亚规则溶体方程获得的(JK): 相似文献
2.
缅甸硬玉岩地区的热液型钠长石岩 总被引：2，自引：0，他引：2
产于俯冲带内的低温高压带的由单矿物构成的硬玉岩通常伴有钠长石岩,目前对于硬玉岩研究的关注度较高,而对于钠长石岩则相对较低,很少有相关论文报导.产于缅甸翡翠矿区的钠长石岩,经常与硬玉岩相伴而生,是良好的研究样品.钠长石岩的主要矿物成分是低温钠长石,其次含有硬玉、绿辉石、透辉石等辉石类矿物和钠透闪石、蓝透闪石、镁钠闪石等闪石类矿物,此外还有钠沸石等.钠长石沿着解理和裂隙交代硬玉,说明钠长石形成晚于硬玉岩.钠长岩中的主要组成矿物钠长石的形成温度小于300℃,且其形成压力小于0.5kb,推测是在硬玉岩抬升程中通过交代与沉淀作用形成.其内的透辉石有两种类型,一类可能是被交代的硬玉中的透辉石组分会渐进增加,最终形成透辉石.另一类是被绿辉石包裹的透辉石残留,其很有可能是早期来自地幔楔或者俯冲带岩石中的矿物残留,即异剥钙榴岩或辉石岩类,可以视作硬玉化绿辉石岩和硬玉化异剥钙榴岩的矿物学证据.热液型钠长石岩的存在进一步说明缅甸翡翠矿区钠化热液存在现象的普遍性与穿越性. 相似文献
3.
根据缅甸硬玉岩的化学成分,利用相平衡热力学模拟硬玉岩的成因理论,采用对称溶体的模型表达式:RTlnγi=-∑∑(X0K-Xk)(X0j-Xj)Wkj,根据Holland等的热力学数据库,计算得出硬玉岩中4种端元矿物硬玉(Jd)、普通辉石(Acm)、透辉石(Di)与钙铁辉石(Hed)的Wkj值. 相似文献
4.
翡翠的化学成分和矿物组成特征 总被引：2，自引：0，他引：2
对不同颜色的翡翠进行了较系统的化学成分和矿物成分研究，发现翡翠的化学成分和矿物 成分与翡翠的颜色之间有一定的内在规律。随着翡翠的绿色由浅变深，Ｃｒ、Ｍｇ、Ｃａ等元素的含量逐渐增 高，硬玉和绿辉石矿物成分逐渐向透辉石－钙铁辉石系列演化。 相似文献
5.
翡翠的矿物成分和辉玉的分类 总被引：5，自引：0，他引：5
翡翠主要由硬玉（ＮａＡｌＳｉ２Ｏ６）矿物集合体组成。除硬玉外,有时还含有一些其它的单斜辉石类矿物,现在已经确定的有：铬硬玉、透辉质硬玉、钠铬辉石质硬玉、绿辉石、钠铬辉石质绿辉石、透辉质钠铬辉石、硬玉质钠铬辉石、钠铬辉石、透辉石、硬玉质单斜顽火辉石、透辉质单斜顽火辉石、霓辉石和霓石等。只有主要由硬玉的摩尔百分数〉５０％的硬玉矿物组成的玉石才能叫翡翠。而主要由其它单斜辉石类矿物组成的玉石,应分别叫霓石 相似文献
6.
对于具有限混溶或原子有序分布的简单二元固溶体来说,已结合其自由能曲线来预测一种体系的相关系和出溶机理。有序过程的特征影响着出溶机理的适用性.如果有序化作用是二步(较高)有序时,则整个过程以连续机理占优势,而所描述的一种“条件旋节分解”(“Conditional spinodal”)(Allen 和 Cahni 1976)只有对序与无序端员组分之间起着决定作用.对于一步有序来说,有序相仅能经成核与生长来沉淀无序相.用透射电子显微镜所观察到的绿辉石徼细结构包括出溶页片和反相晶畴,并且在所选择的样品中它们之间的关系已用于解释地质条件下起控制作用的出溶机理。绝大多数绿辉石几乎都经历了阳离子的有序过程,然后保持均一体,或通过旋节分解作用出溶一种无序辉石。连续出溶机理占优势已用来说明 C2/c→P2/n 转换可以是二步(较高)有序的.现已提供了一种硬玉——普通辉石的可能相图,它是以这种理论为基础的,即在低温下无序端员组分之间应该是有限混溶的,而中间成分(绿辉石)的阳离子是有序的,两者迭加在一条溶相线上。这就完全解释了观察到的许多微细结构,并与在含杂质硬玉和绿辉石之间、绿辉石和钠辉石之间存在宽阔二相区的岩相学证据相符合。加入锥辉石所产生的影响类似于增温效应,所以,也就能够预测硬玉——锥辉石——普通辉石的相关系。 相似文献
7.
本文讨论了熔体中矿物的热流控制生长。作者按照传导方程的自由边界问题,在地质条件容许的范围内,导出了计算矿物生长速度和生长大小的公式,并以已有实验数据对计算公式进行了验证,还得到了计算透辉石-钙铝辉石固溶体生长速度和生长大小所需的导热系数。讨论认为本文模型适用于自然界在较高温度下从单组份熔体中缓慢结晶的矿物。 相似文献
8.
榴辉岩相变质岩石的温压研究对理解高压-超高压变质带的形成和演化具有重要意义,但西南天山低温榴辉岩运用石榴石-绿辉石（-多硅白云母）温压计计算的压力普遍低于相平衡模拟的结果.为此,在Zhang et al.（2017） 对含霓辉石榴辉岩研究结果的基础上,对该区域内榴辉岩及其脉体中的绿辉石进行了岩相学和矿物化学的研究,结果表明绿辉石普遍发育环带结构:从核部到边部,Fe3+含量降低,Al含量增加,Fe3+/Al比值的降低对应于霓石含量的降低和硬玉含量的升高.相平衡模拟中硬玉分子等值线的计算结果表明具有最高硬玉含量的边部绿辉石在降压阶段生长.因此,具有最高含量的硬玉组分的绿辉石并不一定代表峰期压力,在应用石榴石-单斜辉石（-多硅白云母）传统温压计时需谨慎,尤其是应用于低温的、具有复杂环带模式的矿物组合时要尤为慎重. 相似文献
9.
根据矿物成分及其结构演变,将大别山榴辉岩的退变质过程分为三个阶段:贫流体阶段、弱流体阶段和富流体阶段。贫流体阶段发生于榴辉岩相环境中,其主要作用是柯石英-石英和文石- 方解石等同质多象转变、石榴子石和绿辉石等的重结晶,以及绿辉石中硬玉和钠长石的固溶体出溶等。弱流体阶段发生于榴辉岩相退变质的晚期,含水矿物闪石、绿帘石和云母,以及钠长石等低压矿物大量形成之前,其标志是蓝晶石变斑晶和金红石脉的形成,以及浸染状金红石的富集成矿。富流体阶段始于低级角闪岩相退变质环境,并可能一直持续到近地表处。该阶段以出现大量含水和挥发份的矿物(如闪石、绿帘石、多硅白云母、钠云母、黑云母、磷灰石和碳酸盐等)为特征。围绕石榴子石和绿辉石的闪石次变边、闪 相似文献
10.
俄罗斯白海活动带Uzkaya Salma地区榴辉岩中发现的绿纤石形成于榴辉岩化早期亚绿片岩相阶段。该绿纤石多以包体形式存在于退变榴辉岩的变斑晶石榴石矿物中,并与榍石、金红石、单斜辉石、绿泥石、绿帘石、石英等矿物伴生,极少量单颗粒绿纤石包裹在基质单斜辉石(透辉石)矿物中,呈浑圆状。绿纤石成分上属于铝绿纤石和铁绿纤石,其中以铝绿纤石为主。在详细的岩相学研究基础上,通过相平衡计算,结合矿物温压计计算结果,发现含绿纤石榴辉岩共经历了4阶段的变质演化:Ⅰ早期进变质阶段,以石榴石中的绿纤石+绿泥石+绿帘石+石英等矿物包裹体为特征,依据实验岩石学研究的矿物组合绿纤石+绿泥石+石英和铁绿纤石+绿帘石稳定域,估算该变质阶段温压条件t=160~320℃,p=0.2~0.8 GPa;Ⅱ峰期榴辉岩相阶段,矿物组合为石榴石+Di-Pl后成合晶推测的绿辉石+金红石±角闪石+石英,石榴石核部镁等值线和绿辉石硬玉分子等值线限定其峰期温压条件为t=725~740℃,p=1.4~1.5 GPa;Ⅲ高压麻粒岩相退变质阶段,矿物组合为石榴石+透辉石+角闪石+斜长石+石英,石榴石-单斜辉石温度计和后成合晶中斜长石钙等值线限定该阶段的温压条件t=725~750℃,p=1.1~1.3 GPa;Ⅳ晚期角闪岩相退变质阶段,矿物组合角闪石+斜长石±黑云母+石英,相平衡计算和角闪石-斜长石温度计限定温压条件为t=670~700℃,p=0.7~0.9 GPa。综上,确定了俄罗斯白海活动带Uzkaya Salma地区含绿纤石榴辉岩具有顺时针的p-T演化轨迹,峰期对应的地温梯度为15℃/km,俯冲进变质阶段经历了绿纤石-绿帘石相变质,由峰期榴辉岩相到退变质高压麻粒岩相具近等温降压的特征。研究表明,板块的"冷"俯冲作用在地球演化早期太古宙时期就可能出现了。 相似文献
11.
Non-ideality in mineral solid solutions affects their elastic and thermodynamic properties, their thermobaric stability, and the equilibrium phase relations in multiphase assemblages. At a given composition and state of order, non-ideality in minerals is typically modelled via excesses in Gibbs free energy which are either constant or linear with respect to pressure and temperature. This approach has been extremely successful when modelling near-ideal solutions. However, when the lattice parameters of the solution endmembers differ significantly, extrapolations of thermodynamic properties to high pressures using these models may result in significant errors. In this paper, I investigate the effect of parameterising solution models in terms of the Helmholtz free energy, treating volume (or lattice parameters) rather than pressure as an independent variable. This approach has been previously applied to models of order–disorder, but the implications for the thermodynamics and elasticity of solid solutions have not been fully explored. Solid solution models based on the Helmholtz free energy are intuitive at a microscopic level, as they automatically include the energetic contribution from elastic deformation of the endmember lattices. A chemical contribution must also be included in such models, which arises from atomic exchange within the solution. Derivations are provided for the thermodynamic properties of n-endmember solutions. Examples of the use of the elastic model are presented for the alkali halides, pyroxene, garnet, and bridgmanite solid solutions. Elastic theory provides insights into the microscopic origins of non-ideality in a range of solutions, and can make accurate predictions of excess enthalpies, entropies, and volumes as a function of volume and temperature. In solutions where experimental data are sparse or contradictory, the Helmholtz free energy approach can be used to assess the magnitude of excess properties and their variation as a function of pressure and temperature. The formulation is expected to be useful for geochemical and geophysical studies of the Earth and other planetary bodies. 相似文献
12.
Al, Ca, Mg and Na montmorillonites were reacted with acid aqueous solutions in order to test the assumption of equilibrium underlying solubility determinations of thermodynamic properties of montmorillonite. The value calculated for the equilibrium constant varied with pH over the pH range 1.5–4.2. Hence montmorillonite was not in a unique state of equilibrium with all solutions over this range. Therefore the derivation of thermodynamic properties of montmorillonite by the application of a single step dissolution equation to results of solubility studies in mildly acidic solutions is invalid. Indications of solute activity control by a secondary solid phase were given by: (1) the dependence of the solution concentrations of some, but not all, montmorillonite constituent elements upon each other; and (2) a lack of congruency in the dissolution of montmorillonite. These indications were confirmed by a principal components statistical analysis, which showed that the solution activities of Si, Al and H after long-term treatments of the mineral from undersaturation were always related by the same expression. This particular expression is equivalent to an equilibrium constant for the reversible dissolution of a secondary solid phase that is enriched in silicon by comparison with montmorillonite. An aluminous solid phase was also shown to be formed. 相似文献
13.
广西拉么Zn—Cu矿床中夕卡岩的主要矿物特点与Ca—Fe—Si—C—O体系T—lgfO2图解 总被引：1，自引：0，他引：1
用电子探针数据研究了该矿床中主要夕卡岩矿物特点及其变化规律。采用理想结晶溶液固溶体位置混合模式,计算了石榴子石和辉石矿物对中钙铁榴石和钙铁辉石的摩尔分数。在计算纯固相和流体相参加的反应抵达平衡时的边界方程中,加上理想结晶固溶体中端元组分摩尔分数的修正项后,我们便可以计算出有纯固相、流体相和理想结晶溶液固溶体参加反应的在给定T、P条件下的lgfo_2值。计算结果表明:无变度点4周围的Hed+And+Wol组合对本矿区具有重要的地质地球化学意义。 相似文献
14.
胶南榴辉岩矿物氧同位素平衡及其Sm-Nd年代学制约 总被引：2，自引：4，他引：2
对苏鲁地体中的胶南榴辉岩进行了矿物氧同位素分析，并与同一手标本矿物的Sm-Nd内部等时线定年和Nd-Sr同位素分布进行了对比。研究表明，石榴子石与绿辉石之间的氧同位素平衡与否能够对矿物Sm-Nd同位素体系的平衡状况和内部等时线定年结果的有效性给予直接制约。合理的石榴子石＋绿辉石Sm-Nd内部等时线年龄产于两矿物之间达到并在峰变质条件下保持氧同位素平衡的样品中，而两矿物之间处于氧同位素不平衡的样品不能给出正确的Sm-Nd内部等时线年龄。同一矿物在手标本尺度出现显著的O-Nd-Sr同位素不均一性，据此对这些元素在石榴子石和绿辉石中的扩散速率顺序进行了估计，不仅得到了与实验扩散系数相吻合的结果，而且由此估计出在峰变质条件下达到矿物内部同位素均一化所需要的时间应大于10Ma。 相似文献
15.
Michael A. Carpenter 《Contributions to Mineralogy and Petrology》1980,71(3):289-300
The free energy curves for simple binary solid solutions with limited miscibility or atomic ordering have been combined to
predict the phase relations and exsolution mechanisms for a system in which both ordering and exsolution are possible. The
nature of the ordering process affects which exsolution mechanisms may be used. If the ordering is second (or higher) order
in character then continuous mechanisms predominate and a ‘conditional spinodal’ (Alien and Cahn, 1976) can be described which
operates between ordered and disordered end members. For a first order case, the ordered phase can only precipitate a disordered
phase by nucleation and growth.
Microstructures in omphacites observed by transmission electron microscopy include exsolution lamellae and antiphase domains
and the relations between them in selected specimens have been used to interpret the exsolution mechanisms which operated
under geological conditions. It appears that most omphacites undergo cation ordering, and then remain homogeneous or exsolve
a disordered pyroxene by spinodal decomposition. The predominance of continuous mechanisms has been used to indicate that
the C2/c→P2/n transformation may be second (or higher) order in character.
A possible phase diagram for jadeite-augite is presented. It is based on the idea that there should be limited miscibility
between the disordered end members at low temperatures and that the cation ordering at intermediate compositions (omphacite)
is superimposed on a solvus. It is adequate to explain many of the observed microstructures and fits with petrographic evidence
of broad two phase fields between impure jadeite and omphacite and between omphacite and sodic augite. The effect of adding
acmite is analogous to increasing temperature so that the phase relations for jadeite-acmite-augite can also be predicted. 相似文献
16.
Mixing properties for muscovite–celadonite–ferroceladonite solid solutions are derived from combining available experimental phase equilibrium data with tabulated thermodynamic data for mineral end‐members. When a partially ordered solution model is assumed, the enthalpy of mixing among the end‐members muscovite–celadonite–ferroceladonite is nearly ideal, although the Gibbs energies of muscovite–celadonite and muscovite–ferroceladonite solutions are asymmetric due to an asymmetry in the entropy of mixing. Thermodynamic consistency is achieved for data on phengite compositions inassemblages with (a) pyrope+kyanite+quartz/coesite (b) almandine+kyanite+quartz/coesite (c)talc+kyanite+quartz/coesite and (d) garnet–phengite pairs equilibrated both experimentally at high temperatures and natural pairs from low‐grade schists. The muscovite–paragonite solvus has been reanalysed using the asymmetric van Laar model, and the effects of the phengite substitution into muscovite have been quantitatively addressed in order to complete the simple thermodynamic mixing model for the solid solution among the mica end‐members. Results are applied to a natural pyrope–coesite–phengite–talc rock from the Western Alps, and to investigate the conditions under which biotite‐bearing mica schists transform to whiteschist‐like biotite‐absent assemblages for average pelite bulk compositions. 相似文献
17.
Robert G. Berman 《Geochimica et cosmochimica acta》1984,48(4):661-678
A thermodynamic model is proposed for calculation of liquidus relations in multicomponent systems of geologic interest. In this formulation of mineral-melt equilibria, reactions are written in terms of the liquid oxide components, and balanced on the stoichiometry of liquidus phases. In order to account for non-ideality in the liquid, a ‘Margules solution’ is derived in a generalized form which can be extended to systems of any number of components and for polynomials of any degree. Equations are presented for calculation of both the excess Gibbs free energy of a solution and the component activity coefficients.Application to the system CaO-Al2O3-SiO2 at one atmosphere pressure is achieved using linear programming. Thermodynamic properties of liquidus minerals and the melt are determined which are consistent with adopted error brackets for available calorimetric and phase equilibrium data. Constraints are derived from liquidus relations, the CaO-SiO2 binary liquid immiscibility gap, solid-solid reactions, and measured standard state entropies, enthalpies, and volumes of minerals in this system.Binary and ternary liquidus diagrams are recalculated by computer programs which trace cotectic boundaries and isothermal sections while checking each point on a curve for metastability. The maximum differences between calculated and experimentally determined invariant points involving stoichiometric minerals are 17°C and 1.5 oxide weight per cent. Because no solid solution models have been incorporated, deviations are larger for invariant points which involve non-stoichiometric minerals.Calculated heats of fusion, silica activities in the melt, and heats of mixing of liquids compare favorably with experimental data, and suggest that this model can be used to supplement the limited amount of available data on melt properties. 相似文献
18.
M. A. Carpenter 《Contributions to Mineralogy and Petrology》1978,67(1):17-24
Omphacites with a range of compositions from the blueschist rocks of Syros, Greece and from included blocks in serpentinite from the Motagua fault zone, Guatemala, have been examined by transmission electron microscopy. The complex microstructures observed are all on a fine scale and are composed of exsolution and antiphase features. At least three different assemblages have been identified: (a) a single ordered phase with antiphase domains, (b) two exsolved phases, one ordered and the other disordered and (c) two exsolved phases, both apparently ordered. Selected area electron diffraction patterns provide evidence for P2/n, P2/c, and P2 space groups in different parts of the ordered crystals.The microstructures cannot all be readily explained in terms of a simple equilibrium phase diagram and some are attributed to alternative and metastable transformations. It is suggested that under the low temperature conditions of blueschist metamorphism, omphacite crystallised metastably below its ordering temperature with imperfect cation order. Subsequent development by cation ordering and exsolution was controlled by kinetics, the fastest available transformation being used to give reductions in free energy. Ordering preceded exsolution and may have occurred in a series of steps as predicted by the Ostwald step rule. Slight differences in composition and initial state of order locally influenced which reaction pathway was embarked upon and many of the products may be metastable. Such behaviour is apparently sensitive to thermal history. 相似文献
19.
Peter L. McSwiggen 《Physics and Chemistry of Minerals》1993,20(1):33-41
The minerals of the ternary carbonate system CaCO3 - MgCO3 - FeCO3 represent a complex series of solid solutions and ordering states. An understanding of those complexities requires a solution model that can both duplicate the subsolidus phase relationships and generate correct values for the activities. Such a solution model must account for the changes in the total energy of the system resulting from a change in the ordering state of the individual constituents. Various ordering models have been applied to binary carbonate systems, but no attempts have previously been made to model the ordering in the ternary system. This study derives a new set of equations that allow for the equilibrium degree of order to be calculated for a system involving three cations mixing on two sites, as in the case of the ternary carbonates. The method is based on the Bragg-Williams approach. From the degree of order, the mole fractions of the three cations in each of the two sites can be determined. Once the site occupancies have been established, a Margules-type mixing model can be used to determine the free energy of mixing in the solid solution and therefore the activities of the various components. 相似文献
20.
The behaviour of Li and Mg isotopes during primary phase dissolution and secondary mineral formation in basalt 总被引：1，自引：0，他引：1
Josh Wimpenny Sigurður R. Gíslason Abdelmouhcine Gannoun Philip A.E. Pogge Von Strandmann 《Geochimica et cosmochimica acta》2010,74(18):5259-6026
This study presents lithium (Li) and magnesium (Mg) isotope data from experiments designed to assess the effects of dissolution of primary phases and the formation of secondary minerals during the weathering of basalt. Basalt glass and olivine dissolution experiments were performed in mixed through-flow reactors under controlled equilibrium conditions, at low pH (2-4) in order to keep solutions undersaturated (i.e. far-from equilibrium) and inhibit the formation of secondary minerals. Combined dissolution-precipitation experiments were performed at high pH (10 and 11) increasing the saturation state of the solutions (moving the system closer to equilibrium) and thereby promoting the formation of secondary minerals.At conditions far from equilibrium saturation state modelling and solution stoichiometry suggest that little secondary mineral formation has occurred. This is supported by the similarity of the dissolution rates of basalt glass and olivine obtained here compared to those of previous experiments. The δ7Li isotope composition of the experimental solution is indistinguishable from that of the initial basalt glass or olivine indicating that little fractionation has occurred. In contrast, the same experimental solutions have light Mg isotope compositions relative to the primary phases, and the solution becomes progressively lighter with time. In the absence of any evidence for secondary mineral formation the most likely explanation for these light Mg isotope compositions is that there has been preferential loss of light Mg during primary phase dissolution.For the experiments undertaken at close to equilibrium conditions the results of saturation state modelling and changes in solution chemistry suggest that secondary mineral formation has occurred. X-ray diffraction (XRD) measurements of the reacted mineral products from these experiments confirm that the principal secondary phase that has formed is chrysotile. Lithium isotope ratios of the experimental fluid become increasingly heavy with time, consistent with previous experimental work and natural data indicating that 6Li is preferentially incorporated into secondary minerals, leaving the solution enriched in 7Li. The behaviour of Mg isotopes is different from that anticipated or observed in natural systems. Similar to the far from equilibrium experiments initially light Mg is lost during olivine dissolution, but with time the δ26Mg value of the solution becomes increasingly heavy. This suggests either preferential loss of light, and then heavy Mg from olivine, or that the secondary phase preferentially incorporates light Mg from solution. Assuming that the secondary phase is chrysotile, a Mg-silicate, the sense of Mg fractionation is opposite to that previously associated with silicate soils and implies that the fractionation of Mg isotopes during silicate precipitation may be mineral specific. If secondary silicates do preferentially remove light Mg from solution then this could be a possible mechanism for the relatively heavy δ26Mg value of seawater. This study highlights the utility of experimental studies to quantify the effects of natural weathering reactions on the Li and Mg geochemical cycles. 相似文献