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1.
绿辉石流变学研究的某些进展   总被引：1，自引：1，他引：1  
简要概述了绿辉石的晶体结构、反相畴、显微构造及其变形机制等方面的研究现状与进展。结合大别山榴辉岩中的最新研究成果，着重讨论了其构造物理学研究意义，认为绿辉石晶体结构的有序化不仅是温度和化学成分的函数，而且是晶内应变程度的函数。  相似文献   

2.
Available experimental data on mixing of disordered C2/c clinopyroxenes in the system diopside-jadeite-hedenbergite-acmite are reviewed and evaluated. Because the methods used to determine jadeite activity suffer from severe uncertainty at high jadeite mol fractions, these data cannot be used to infer asymmetry in the jadeite-diopside or the jadeite-hedenbergite solid solutions. If the measurement uncertainties are taken into account, a single parameter (regular, or reciprocal energy) suffices to describe the mixing properties of these two solid solutions. It is argued that a two-site entropy of mixing satisfies the experiments and is consistent with the C2/c disordered nature of the solid solutions; the data in the range 600–1300° C are consistent with a temperature-independent interaction energy, implying no discernible excess entropy. The available experimental data imply W=26±2 kJ mol–1 for jd-di, and W=25±3 kJ mol–1 for jd-hd, solid-solutions. Landau theory for a tricritical phase transformation (C2/c-P2/n) is in good agreement with the calorimetrically determined disordering enthalpy, and may be used to derive a simple expression for the activities in ordered omphacite solid solutions. The derived activities of jadeite at 600° C in ordered omphacites are remarkably close to those reported previously for short-range ordered pyroxenes. A simple model is presented for determining the activities of end-members in the system jadeite-diopside-hedenbergite-acmite.  相似文献   

3.
自然界中矿物多以固溶体形式存在,据其晶体化学特征计算热力学性质是开展矿物成因理论研究的基础。本文引入描述二元矿物固溶体热力学性质的假三元模型,计算得到了透辉石-硬玉固溶体系列的热力学性质。该模型通过构造一种高度有序的中间相,同时考虑长程和短程有序效应,基于热力学平衡态矿物固溶体自由能最低的规律,可以计算特定组分下矿物的平衡自由能、焓和熵等热力学参数。本文针对透辉石-硬玉固溶体体系,取绿辉石为其中间有序态,计算了其活度-成分关系和温度-组分相图等,发现绿辉石随温度升高的有序无序相变为一级相变,相变温度为1 148±25 K,与实验研究结果一致。本文获得的透辉石-绿辉石-硬玉体系的热力学参数可用于视剖面图方法研究MORB成分的岩石的榴辉岩相变质作用过程。  相似文献   

4.
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   

5.
A pair approximation is used to estimate the effects of short-range order on the thermodynamic properties of aluminous clinopyroxenes on the joins diopside (CaMg-Si2O6)-jadeite (NaAlSi2O6) and diopside-CaTs (CaAl2SiO6). The generalized pair approximation is the simplest model for concentrated solutions which includes short-range order. Short-range order is expected to be especially significant in coupled solid solutions, such as aluminous pyroxenes, since atoms of different valence substitute for each other. The calculations show that the random model, in which the configurational entropy is calculated as if atoms on each crystallographic site mix randomly, is appropriate as a first approximation. The excess entropy relative to the random model behaves regularly, is always negative, and becomes more negative as temperature decreases or the ordering energies increase. The excess entropy relative to the random model can be modeled reasonably well with a simple power series, or Margules-type, formulation. In contrast, the excess entropy relative to a molecular model, in which the ideal activity is assumed to be equal to some mole fraction, is irregular, can be positive or negative, and even changes in sign with variations in temperature and composition. The configurational enthalpy is positive at high temperatures, and becomes negative with decreasing temperature or increasing ordering energy. The mixing enthalpy can have non-configurational contributions, in addition to the effective short-range configurational contributions considered explicitly. The pair approximation predicts an ordering transition from C2/c to P21/n for CaTs and diopside-CaTs solutions at moderate to low temperatures, respectively. A field where C2/c orders to C2 is also found. A higher order approximation, different relative ordering energies, or quantitative consideration of strain contributions is required to account for the C2/c to P2/n transition in omphacites. There is no justification for molecular models, in which the configurational entropy is calculated as if endmember “molecules” were mixing in the crystal, in either concentrated or dilute solutions. Molecular models do not represent limiting ordered states for coupled solid solutions.  相似文献   

6.
Swelling clays in stone can generate damaging stresses during a wetting or a drying cycle, which lead to deterioration of building stones such as Portland Brownstone. There are two primary types of swelling identified for clays: short-range, ordered intracrystalline swelling, and long-range, continuous osmotic swelling. Identification of the swelling mode is important for understanding and ultimately preventing swelling damage. Through comparison of XRD and swelling experiments with cationic pretreatments and organic solvents, we demonstrate that intracrystalline swelling is the primary mode of swelling present in three different stones, including Portland Brownstone. The results highlight the importance of the counterbalancing cation to the swelling process, and a method for characterizing the intracrystalline swelling in sandstones is developed. Finally, the implications of long-term swelling behavior for stones are discussed.  相似文献   

7.
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8.
Two Alpine eclogite bodies, sampled in metaophiolitic complexes of the Piemonte Zone, have been studied for geothermometry. It is demonstrated that temperature estimates, by both exchange thermometry and sizes of antiphase domains in omphacites, give rise to erratic results when the defect structures of the minerals are not taken into account. Microstructural criteria, by means of both optical and TEM microscopy, for reliable thermometry in low-temperature eclogites are disscussed. The dynamically recrystallized grains are the more suitable sites for the application of exchange thermometry, while only low-strained omphacites can be used for thermometry based on APD's.  相似文献   

9.
200 kV and 300 kV HREM images of mullite with beam direction parallel to [010] and [100] have been compared with extensive multi-slice calculations of structure models with different oxygen vacancy arrangements. The simulations reveal that changes of the contrast pattern in HREM images are correlated with enhanced vacancy concentrations and coupled cation shifts (Al*). Furthermore, the direct relationship between contrast variation and projected vacancy concentration permits the detection of 20% oxygen vacancies along [010] and [100]. An analysis of HREM images indicates preferred orientations of vacancies parallel to 〈102〉 in the (010) plane, whereas the (010) plane yields arrangements parallel to 〈012〉 and 〈001〉, resulting in an average direction of 〈013〉. Distances of 1.5a and 1.5b between these arrangements result from preferred inter-vacancy correlation vectors of 1/2 〈310〉 and 1/2 〈130〉 in the (001) plane. The investigated 2:1 and 3:2-mullites (x = 0.40 and x = 0.25) do not show long-range ordered arrangements of oxygen vacancies, but reveal the composition-dependent formation of short-range order regions of enhanced vacancy concentrations. These regions are distributed in a matrix with a minor degree of order.  相似文献   

10.
本文以中国大陆科学钻探主孔0～2000m岩芯中的榴辉岩为对象,运用EMPA和LA-ICP-MS技术,系统测定了榴辉岩中石榴石和绿辉石的主量与微量元素组成,并据此讨论了它们的成岩成矿意义.研究结果表明,CCSD主孔榴辉岩中石榴石富重稀土和Sc、Y、Co,而绿辉石则富中稀土和Pb、Sr、V,石榴石和绿辉石的高场强元素(特别是Nb、Ta)含量均很低.石榴石存在不同程度的Ce负异常,指示榴辉岩的形成过程中卷入有地表氧化条件下形成的风化沉积物.石榴石具有低的Zr/Y比值,绿辉石普遍具有高的Sr含量,这些特征说明榴辉岩(特别是高钛榴辉岩)的原岩可能为遭受过壳源物质混染与交代的富集地幔部分熔融的产物.高钛与低钛榴辉岩中石榴石和绿辉石在主量及微量元素组成上存在一定差别,总体而言,高钛榴辉岩中石榴石具高的MgO含量和较高的MgO/TFeO比值,以及较高的稀土和Sc含量,而绿辉石则相对富TFeO、MnO,并具有较高的Sr、Zr、Hf含量.高钛榴辉岩中石榴石和绿辉石常出现不同程度的Eu正异常,Cr含量均显著低于低钛榴辉岩.综合分析表明,高钛榴辉岩的原岩最可能为富斜长石的辉长质侵入岩,原岩组成的差异应是导致二类榴辉岩中石榴石和绿辉石矿物化学组成存在差异的主要原因.  相似文献   

11.
梁金龙  孙晓明  徐莉  翟伟  汤倩  梁业恒 《地质学报》2006,80(12):1904-1910
单斜辉石中发育石英出溶体是UHP变质作用的典型矿物学标志之一,在世界上著名UHP变质地体中屡有发现。本文利用激光Raman光谱和电子探针分析在中国大陆科学钻探先导孔(CCSD-PP1)榴辉岩岩心的绿辉石中发现了大量石英(棒)出溶现象。通过与CCSD主孔榴辉岩各种赋存形式的绿辉石成分对比,发现含石英出溶体的绿辉石具有超硅特征,这是出溶现象发生的决定性因素之一。结合高压实验岩石学资料,提出在UHP变质的峰值期部分Si进入六次配位的Si-O八面体位置,压力降低这部分Si析出,形成石英出溶体的出溶机制。结合新的矿物学研究进展,认为绿辉石中出溶石英所标志的压力应远大于前人提出的2.5GPa,意味着苏鲁超高压变质带陆壳物质的俯冲深度要大于目前一般认为的80~120km范围。  相似文献   

12.
This contribution presents the results of a numerical study of karst denudation on limestone plateaux. The landscape evolution model used incorporates not only long-range fluvial and short-range hill-slope processes, but also large-scale chemical dissolution of limestone surfaces. The relative efficiencies of fluvial and chemical processes are of equal importance to the landscape evolution of a plateau dropping to sea level along an escarpment. While fluvial processes have an impact confined mostly to river channels, the karst denudation process is more uniform, removing material also from the plateau surface. The combined effect of both processes results in a landscape evolution almost twice as effective as the purely erosional evolution of an insoluble landscape.  相似文献   

13.
The elastic and thermodynamic properties of Li2O for high pressures are presented. For cubic Li2O, model effective interatomic interaction potential incorporating long-range Coulomb, charge transfer interactions, covalency effect, Hafemeister and Flygare type short-range overlap repulsion extended up to the second neighbor ions and van der Waals interactions is formulated. Both charge transfer interactions and covalency effect apart from long-range Coulomb are important in revealing high-pressure-induced associated volume collapse, elastic, and thermodynamical properties. The elastic constants, Debye temperature, and thermal expansion coefficient obtained are in good agreement with the available experimental data and other theoretical results. The Li2O is mechanically stiffened, thermally softened, and brittle in nature as inferred from the pressure-dependent elastic constants behavior. To our knowledge, this is the first quantitative theoretical prediction of the pressure dependence of elastic, thermal, and thermodynamical properties of Li2O and still awaits experimental confirmation.  相似文献   

14.
This paper describes a geostatistical method, known as factorial kriging analysis, which is well suited for analyzing multivariate spatial information. The method involves multivariate variogram modeling, principal component analysis, and cokriging. It uses several separate correlation structures, each corresponding to a specific spatial scale, and yields a set of regionalized factors summarizing the main features of the data for each spatial scale. This method is applied to an area of high manganese-ore mining activity in Amapá State, North Brazil. Two scales of spatial variation (0.33 and 2.0 km) are identified and interpreted. The results indicate that, for the short-range structure, manganese, arsenic, iron, and cadmium are associated with human activities due to the mining work, while for the long-range structure, the high aluminum, selenium, copper, and lead concentrations, seem to be related to the natural environment. At each scale, the correlation structure is analyzed, and regionalized factors are estimated by cokriging and then mapped.  相似文献   

15.
The ordering of Al and Si in Mg cordierite Mg2Al4Si5O18 is considered using computer simulation. First the enthalpy of interaction J ij between sites is derived by computer modelling 101 different Al/Si configurations and analysing their energies. They are compared with similar results for three other minerals and with ab initio calculations to assess the whole approach. Secondly the ordering process is studied using Monte Carlo simulation applied to the J ij . The ordering phase transition temperature T c is found as 1800°C in reasonable agreement with the experimental estimate of 1450° C. These are much lower than the estimate T c(ABW)≈7600°C obtained from Bragg-Williams theory. Strong short-range order sets in below T c(ABW), and the reasons for much lower temperature T c of long-range ordering are discussed. Strong short-range also sets in very rapidly in a simulated anneal, in agreement with experiment. Thirdly an attempt is made to compare our calculated enthalpies directly with the results of NMR and calorimetry experiments, not completely successfully. A free energy ΔG≈4.6 eV for the activation barrier for ordering is suggested.  相似文献   

16.
The enthalpies of solution of seven synthetic clinopyroxenes on the join CaMg2Si2O6 (diopside)-NaAlSi2O6 (jadeite), of two natural low-Fe ordered omphacites near the 1:1 composition, and of a nearly pure natural jadeite, were measured in molten Pb2B2O5 at 970 K. Enthalpies of solution of the natural omphacites experimentally disordered at 1350°C and 30 kbar were also measured.The synthetic clinopyroxenes have positive excess enthalpies of mixing, which can be expressed by a symmetrical function ΔHmix = WHXJdXDi, with WH = 7250 ±950 calories. The enthalpy of disordering of the two natural omphacites averages 1.8 kcal, which is nearly the same as the excess enthalpy of mixing of a 1:1 disordered pyroxene.The interaction parameter, WH, can be shown to be essentially equivalent to ΔG° of the reciprocal reaction: CaMgSi2O6 + NaAlSi2O6 = CaAlSi2O+6 + NaMgSi2O?6 M-site cation distribution data of natural omphacites heat-treated at 1000°C (Aldridgeet al., 1978) lead to ΔG° = 7200 cal for the above reaction, in good agreement with the calorimetric WH. The reciprocal solution theory with ΔG° = 7200 cal predicts closely the activities of NaAlSi2OP6 in jadeite-diopsides found from phase equilibrium measurements at 600°C (Holland, 1979a) and is nearly equivalent to an entropically ideal two site mixing model with a (fictive) WH of 5800 cal.Jadeite-diopside solid solutions near the 1:1 composition at temperatures of 1000–1500 K are ‘pseudoideal’; that is, they have nearly the free energies of ideal one-site mixtures (Ganguly, 1973). If the order-disorder transition is nearly first-order at about 1000 K, as suggested by Fleetet al. (1978), the pseudo-ideality holds also for ordered omphacites at least somewhat below 1000 K.  相似文献   

17.
大气动力学方程组全局分析的研究进展   总被引：5，自引：1，他引：4  
把天气预报问题提成初值问题的反问题,可以使用多时刻的历史资料去补充和完善数值预报模式。借助于几何直观可以对大气动力学方程组的极限解集进行全局定性分析,运用胞 概念和方法可以对大气的数值模式的整体特征进行了全局分析和借助概率论的语言进行统计描述。还给出“气候”这个模糊概念的严格的数学定义及定量研究大气可预测性问题的途径。全局分析是研究气候不同于简单初值问题的另一条道路。综述了这方面研究的最新进展。  相似文献   

18.
Essentially, quickclays are products of glaciation which accounts for their limited distribution; other modes of development being of lesser importance. Glacial grinding provides the fine silt and clay sizes required to constitute quickclays. Two major factors account for the geotechnical properties, a composition factor related to material comprising the soil system and a leaching factor, the effectiveness of which is related to the clay-mineral content of the soil.Soils can be divided into three types, based on criteria of particle size and type of interparticle bond. Among the latter are long-range active bonds, typical of true clay-mineral systems; and short-range inactive bonds such as are observed between two quartz particles. The three main soil types have: (a) small particles and long-range forces - the bond/weight ratioR is high; (b) small particles and short-range forces ? R > 1 ; and (c) large particles and short-range forces - i.e., the sands, andR < 1. Quickclays fall more conveniently into type (b) than into type (a) in as much as the most important property is a preponderance of inactive bonds in the soil system. This is achieved by a high content of non-clay mineral particles, and also may be assisted by leaching and cementation. If more than a critical proportion of long-range bonds are present, the required very high sensitivity does not occur.The initial failure of the soil might be treated as tensile using a volume failure criterion; the low settling velocity of the very small (≈ 1?2 μm) particles allows the solid-liquid transformation to occur after a modest shock loading. Observations of low thixotropy, lack of secondary settlement and sudden failure in compression tests can be explained by requirements of particle size and material.  相似文献   

19.
Mechanisms controlling the activity of free aluminum (Al) in Bw1 horizons of soils developed from volcanic ash deposits in Japan were investigated by means of acid-base titrations and kinetic studies. In a Bw1 horizon, with a high content of acid-oxalate extractable Al, soil solution reached equilibrium with short-range ordered aluminosilicates in the order of days. Relatively fast kinetics of the release and precipitation of Al and Si indicate a high reactivity of short-range ordered aluminosilicates in the soil. In the Bw1 horizon of an adjacent soil, with a high content of crystalline clay minerals like halloysite and interlayered vermiculite, solution remained well undersaturated with respect to short-range ordered aluminosilicates and aluminum hydroxide. Apparent equilibrium with respect to halloysite occurred after more than 30 days. This halloysite ( (25 °C)) has a solubility that is less than that reported in the literature ( (25°C)). Our findings suggest that different reactive aluminosilicates may control the activity of free Al in sub-surface horizons of volcanic ash soils with different mineralogy.  相似文献   

20.
The Upper Jurassic Marls of Mikulov present a formation that is considered to be the most promising strata to produce hydrocarbons in the Vienna basin. The marls are composed of dark pelagic marlstones that frequently contain layers of limestone with thickness reaching several hundreds of meters. Twenty-seven core samples from selected wells located in the south-eastern portion of the Czech Republic representing depths ranging from 2300 to 4500 m were analyzed by x-ray diffraction to assess bulk mineralogy and the progress of smectite illitization.Bulk mineralogy of the Mikulov Marls comprises carbonates (mean value = 54.4 mass%), clay minerals (26.6 mass%), quartz (15.0 mass%), and feldspar (1.6 mean%). In the decreasing order, the clay mineral fraction is composed of illite/mica, kaolinite, illite-smectite, and chlorite. The amount of smectite in illite-smectite decreases with depth from 70% to 28%. There is a change from random to ordered interstratification at the depth of 3300 m. The transition from short-range ordering (R1) to long-range ordering (R3) occurs at depths greater than 4,500 m.There was a good correspondence between thermal maturity parameters: the percentage of smectite in illite-smectite structures and vitrinite reflectance as a parameter of organic matter. The increase of the metamorphic grade was compared in respect to the geothermal gradient with adjacent basins.  相似文献   

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