共查询到19条相似文献，搜索用时 406 毫秒
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《矿物岩石地球化学通报》2017,(1)
水是地球岩浆中的一种主要挥发分。水的存在导致岩石的熔融温度降低,其根本原因在于水易溶于硅酸盐熔体。本文总结了在地球岩石圈温压条件下,水在硅酸盐熔体中的赋存形式、溶解度与水对熔体物理性质的影响。熔体中溶解的水以H_2O分子和OH形式存在。水在熔体中的溶解度随压力的升高而增大。当温压条件位于含水硅酸盐体系的临界曲线之上时,甚至可能形成成分介于硅酸盐熔体和富水流体之间的超临界流体。水使熔体的密度和黏度降低,更易于脱离源区向上运移。水使元素扩散加快,有利于晶体和气泡的生长。水导致熔体的电导率升高,使部分熔融造成的电导率异常更加显著。水对硅酸盐熔体迁移性质的影响以及水的溶解行为都与水的种型分异反应密切相关。在研究与熔融有关的地质过程时必须充分考虑水的作用。 相似文献
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水在岩浆熔体中的溶解机理—水与硅酸盐熔体反应 总被引：2，自引：0，他引：2
本文将有关水－熔体反应研究领域内的最新果归纳为以下几个方面：（１）硅酸盐熔体中水至少以三种方式存在：分子水，羟基和质子，它们的相对丰度是熔体组成，溶解水含量，温度，压力等多种因素的函数；（２）水的溶解使熔体粘度降低，但这并不一定要求Ｓｉ－Ｏ－Ｓｉ键的破坏，质子对Ｎａ＾＋，Ｋ＾＋的置换也产生同样效果；（３）相对于温度和压力而言，熔体的组成对水溶解度的影响程度更高，水的溶解度随富Ｎａ和Ｌｉ组分含量的增 相似文献
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硫在岩浆熔体中的溶解行为综述 总被引：4，自引：0，他引：4
对火山放气过程中硫行为的研究是研究岩浆氧化状态及估算火山排气量的一种有效手段。硫在硅酸盐熔体中的溶解行为与其氧化状态紧密相关,硫在硅酸盐熔体中的溶解度取决于氧逸度、硫逸度和Ｏ２－在熔体中的行为,且熔体中硫的溶解度与其中水的含量呈反比关系。常压条件下硫在熔体中的溶解度与ＳｉＯ２的含量呈反比关系,在还原环境中硫在熔体中的溶解度与熔体中ＦｅＯ含量呈正相关。在氧化性岩浆中硫的溶解度较高,这可能是硫自地幔或下地壳迁移至近地表火山环境中的有效机制。 相似文献
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磷灰石在岩浆中的溶解行为有助于理解熔体的演化、微量元素如REE、U、Th、Sr等的分异和地幔交代流体的形成。本文综述了硅酸盐熔体中温度、熔体成分(Si O2、Ca O、Al2O3、S等)和碳酸盐熔体中温度、Ca O含量等对磷灰石溶解度的影响,介绍了已建立的溶解度模型以及采用模型成功解释实际成岩成矿过程的例子。在概述研究进展的基础上,指出了压力、卤素和高压流体等对磷灰石溶解行为影响的研究的不足。 相似文献
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选取人工合成的简单花岗岩玻璃以及铌锰矿和钽锰矿晶质矿物作为实验初始物,实验研究了100MPa、800℃条件下铌锰矿和钽锰矿在水饱和(或近水饱和)的无磷和含磷简单花岗质熔体中的溶解度。实验结果显示,在过碱质熔体中铌锰矿和钽锰矿的溶解度远高于它们在准铝质和过铝质熔体中的溶解度,但两者之间的溶解度相差不大;在准铝质和过铝质熔体中,铌锰矿的溶解度要明显低于钽锰矿。在过碱质熔体中,铌锰矿、钽锰矿的溶解度与体系中P2O5的含量存在负的线性相关性,即lgKspNb=-0.29×P2O5-2.05(R2=0.96)和1gKspTa=-0.29×P2O5-1.79(R22=0.98);在准铝质熔体中,铌锰矿、钽锰矿的溶解度则随体系中P2O5含量的增大呈逐渐升高趋势;在过铝质熔体中,铌锰矿、钽锰矿的溶解度随体系中P205的含量增大,先表现为降低的趋势,但是当P2O5的含量大于约3%时铌锰矿、钽锰矿的溶解度在误差范围内随P205含量的升高基本保持恒定。上述实验结果产生的主要原因很可能与铌、钽在硅酸盐熔体中的溶解机制以及磷在不同化学组成的硅酸盐熔体中不同的结构作用有关。 相似文献
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中酸性硅酸盐熔体-水体系氢同位素分馏的压力效应 总被引：1，自引：0，他引：1
对0．2－2000MPa条件下钠长石熔体，钾长石熔体以及0．2－150MPa条件下流纹岩熔体－－水体系的氢同位素分馏实验数据进行了筹压拟合，发现硅酸盐熔体与水之间的氢同位素分馏存在显著的压力效应，在800，1000和1200度条件下对钠长石熔体，水体系和流夺熔体－－水体系氢同位素分馏压力方程进行的等温拟合表明，只有在特定的压力条件下才可以用钠长石熔体－水体系来近似流纹岩熔体－－水体系的氢同位素分馏行为，当压力超过临界值时，硅酸盐熔体－水体系氢同位素分馏会发生变化，本文拟合的硅酸盐熔体－水体系氢同位素分馏等值线在P－T空间的形态变化特征与矿物－水体系存在较大差异，依据流纹岩熔体与水之间氢同位素分馏的压力效应，成功地模拟了美国西部Glass Creek流纹岩δD值和水含量变化规律与岩浆去气之间的关系。 相似文献
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秘鲁马库萨尼过铝、富亲石元素的流纹黑曜岩在200MPa、饱和蒸气条件下的实验表明H2O和硅酸盐熔体组分具很高的混溶性。达到饱和时熔体的含水量为11．5±0．5wt％，蒸气中熔体组分相应的溶解度从750℃-775℃时的15wt％（溶解的固体）减少到600℃时的9wt%。在高于液相线温度（＞645℃）时，所研究的元素（B、P、FLiRb、Cs、Be、Sr、Ba、Nb、Zr、Hf、Y、Pb、Th、U、La、Ce、Pr、Nd、Sm、Gd、Tb、Dy、Ho、Er、Tm)的蒸气／熔体分配系数，只有B大于或等于1，其余元素均小于1。 相似文献
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对火山放气过程中硫行为的研究是研究岩浆氧化状态及估算火山排气量的一种有效手段,硫在硅酸盐熔体中的溶解行为与其氧化状态紧密相关,硫在硅酸盐熔３体中的溶解度取决于氧逸度、硫逸度和Ｏ＾２－在溶体中的行为,且熔体中硫的溶解度与其中水的含量呈反比关系。常压条件下硫在熔体中的溶解度与ＳｉＯ２的含量呈反比关系,在还原环境中硫在溶体中的溶解度与熔体中ＦｅＯ含量呈正相关。在氧化性岩浆中硫的溶解度较高,这可能是硫自地 相似文献
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热扩散在地质过程中是否发挥重要作用一直存有争议。本文回顾了热扩散的研究历史和现状,重点总结了热扩散驱动的元素和同位素行为规律,并探讨了温度、硅酸盐组分、压力和氧逸度等因素对热扩散行为的影响。已有的研究表明,稳定热梯度下的硅酸盐热扩散效应类似于结晶分异或AFC过程,可以造成轻、重同位素分别在高温端和低温端富集,而主、微量元素的扩散方向则取决于两端化学势的高低和熔体中的电价平衡。从基性岩浆到酸性岩浆,熔体聚合度增大,黏度增加,热扩散速率明显降低,成网元素的热扩散效应减弱,变网元素则反之;水、氟、氯和硫化氢等挥发组分能增加熔体的非桥氧比例,降低熔体聚合度,因而能显著增强硅酸盐熔体中元素和同位素的热扩散效应。在此基础上,本文提出了当前硅酸盐体系热扩散研究中存在的五个亟需解决的问题,即:1)对不同硅酸盐体系的热扩散规律的研究还不够全面;2)对微量元素的热扩散行为认识不足;3)硅酸盐体系热扩散作用的影响因素及尺度还不够明确;4)热扩散作用的地质与地球化学关键识别标志有待确立;5)硅酸盐体系热扩散作用的理论模型有待建立。尽管硅酸盐体系热扩散的研究还存在诸多不足,但越来越多的证据表明,热扩散是地质过程中不容忽视的一种成分分异机制。这种机制会造成岩浆房或岩浆通道中的元素分异和同位素分馏,可能对于一些成分分异的岩石和矿床的形成具有重要的意义。 相似文献
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以合成花岗岩、水、不同浓度的盐酸溶液、氢氟酸溶液作为反应初始物,在850℃,100 MPa,接近于NNO的条件下开展了金在不同花岗质熔体中溶解度的实验研究,实验固液相产物中的金含量使用石墨炉原子吸收法测定。实验结果显示,金在花岗质熔体中的溶解度变化范围为1.87～156.62μg/g,流体相中金的溶解度为0.31～6.92μg/g;金在熔体相中的溶解度较其在共存液相中的高。花岗质熔体相中金的溶解度明显受熔体化学组成的影响,过碱性富钠花岗质熔体中金的溶解度明显高些;金在花岗质熔体中的溶解度随着熔体中Na2O/K2O摩尔比增大而增大;在氟氯共存岩浆体系中,氟含量变化对金在熔体相中的溶解度影响不明显,而液相中氯含量增大有利于提高金在流体相中的含量。 相似文献
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. Cl solubility in evolved alkaline melts was investigated at 860-930 °C and pressures of 25 to 250 MPa using natural trachytes and a synthetic phonolite equilibrated with subcritical fluids in the H2O-(Na,K)Cl system (i.e. silicate melt coexisted with water-rich aqueous fluid and a saline brine). Fluid phase characteristics were identified by examination of fluid inclusions present in the run product glasses and the fluid bulk composition was calculated by mass balance. The Cl contents of trachytic glasses coexisting with subcritical fluids increase linearly with decreasing pressure from 250 to 25 MPa and range from 0.37 to 0.90 wt%; Cl in the phonolitic glass ranges from 0.35 to 0.59 wt%. These values are approximately twice those found in metaluminous rhyolitic melts under similar conditions. Variations from peralkaline to peraluminous composition has little effect on Cl solubility in trachytes, whereas it is a more important factor in phonolites. More generally, melt structure, in particular non-bringing oxygen, appears to strongly influence Cl solubility in silicate melts. The negative correlation between pressure and melt Cl content is governed by the large negative partial volume of NaCl in the vapour phase. No change in Cl solubility is observed between 200 and 250 MPa. Comparison of our experimental results with Cl abundance in glass inclusion and matrix glass from Italian volcanoes can be used to identify those eruptive products preserved in the geologic record which may have been associated with large Cl emissions. 相似文献
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We have compiled water solubility data for a wide range of natural and synthetic aluminosilicate melts in a search for correlations between melt composition and solubility. The published data reveal some interesting systematics. For example, molar water solubility increases with decreasing silica content in binary and pseudobinary silicates, and much higher solubilities are associated with alkali systems compared to alkaline earth silicate melts. Water solubility increases regularly with decreasing silica content along the silica-nepheline join. From the limited data available for potassium and calcium aluminosilicate melts, these systems appear to behave differently to sodium aluminosilicates. The compiled data are not nearly extensive enough to begin to understand the effects of melt composition on solubility. We suggest that many more systematic studies for a wide range of aluminosilicate melts will be necessary before we can systematize and understand the compositional dependence of water solubility. We have also examined results of experiments designed to probe the details of the water dissolution mechanism, and discuss the present state of interpretation of these data. We conclude that although considerable progress has been made, the water dissolution process is still not well understood at the molecular level, and remains an important research problem. 相似文献
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This paper reviews the results of investigations of melt inclusions in minerals of carbonatites and spatially associated silicate rocks genetically related to various deep-seated undersaturated silicate magmas of alkaline ultrabasic, alkaline basic, lamproitic, and kimberlitic compositions. The analysis of this direct genetic information showed that all the deep magmas are inherently enriched in volatile components, the most abundant among which are carbon dioxide, alkalis, halides, sulfur, and phosphorus. The volatiles probably initially served as agents of mantle metasomatism and promoted melting in deep magma sources. The derived magmas became enriched in carbon dioxide, alkalis, and other volatile components owing to the crystallization and fractionation of early high-magnesium minerals and gradually acquired the characteristics of carbonated silicate liquids. When critical compositional parameters were reached, the accumulated volatiles catalyzed immiscibility, the magmas became heterogeneous, and two-phase carbonate-silicate liquid immiscibility occurred at temperatures of ≥1280–1250°C. The immiscibility was accompanied by the partitioning of elements: the major portion of fluid components partitioned together with Ca into the carbonate-salt fraction (parental carbonatite melt), and the silicate melt was correspondingly depleted in these components and became more silicic. After spatial separation, the silicate and carbonate-silicate melts evolved independently during slow cooling. Differentiation and fractionation were characteristic of silicate melts. The carbonatite melts became again heterogeneous within the temperature range from 1200 to 800–600°C and separated into immiscible carbonate-salt fractions of various compositions: alkali-sulfate, alkali-phosphate, alkali-fluoride, alkali-chloride, and Fe-Mg-Ca carbonate. In large scale systems, polyphase silicate-carbonate-salt liquid immiscibility is usually manifested during the slow cooling and prolonged evolution of deeply derived melts in the Earth’s crust. It may lead to the formation of various types of intrusive carbonatites: widespread calcite-dolomite and rare alkali-sulfate, alkali-phosphate, and alkali-halide rocks. The initial alkaline carbonatite melts can retain their compositions enriched in P, S, Cl, and F only at rapid eruption followed by instantaneous quenching. 相似文献
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The speciation of water in silicate melts 总被引：1，自引：0，他引：1
Edward Stolper 《Geochimica et cosmochimica acta》1982,46(12):2609-2620
Previous models of water solubility in silicate melts generally assume essentially complete reaction of water molecules to hydroxyl groups. In this paper a new model is proposed that is based on the hypothesis that the observed concentrations of molecular water and hydroxyl groups in hydrous silicate glasses reflect those of the melts from which they were quenched. The new model relates the proportions of molecular water and hydroxyl groups in melts via the following reaction describing the homogeneous equilibrium between melt species: H2Omolecular (melt) + oxygen (melt) = 2OH (melt). An equilibrium constant has been formulated for this reaction and species are assumed to mix ideally. Given an equilibrium constant for this reaction of 0.1–0.3, the proposed model can account for variations in the concentrations of molecular water and hydroxyl groups in melts as functions of the total dissolved water content that are similar to those observed in glasses. The solubility of molecular water in melt is described by the following reaction: H2O (vapor) = H2Omolecular (melt).These reactions describing the homogeneous and heterogeneous equilibria of hydrous silicate melts can account for the following observations: the linearity between fH2O and the square of the mole fraction of dissolved water at low total water contents and deviations from linearity at high total water contents; the difference between the partial molar volume of water in melts at low total water contents and at high total water contents; the similarity between water contents of vapor-saturated melts of significantly different compositions at high pressures versus the dependence on melt composition of water solubility in silicate melts at low pressures; and the variations of viscosity, electrical conductivity, the diffusivity of “water,” the diffusivity of cesium, and phase relationships with the total dissolved water contents of melts.This model is thus consistent with available observations on hydrous melt systems and available data on the species concentrations of hydrous glasses and is easily tested, since measurements of the concentrations of molecular water and hydroxyl groups in silicate glasses quenched from melts equilibrated over a range of conditions and total dissolved water contents are readily obtainable. 相似文献
16.
火成碳酸岩及其风化产物是全球战略性关键金属稀土元素(REE)和铌(Nb)的主要来源。因此,对关键金属在火成碳酸岩中的超常富集机理研究具有重要的科学意义。研究表明成矿碳酸岩常常与碱性杂岩体存在密切的时空联系,因而母岩浆应属于碳酸盐化的硅酸盐岩浆,并以霞石岩岩浆为主。针对碳酸岩关键金属矿床的成岩成矿过程,已有实验发现母岩浆在地壳内的演化过程中,既可以通过分离结晶作用,也可以通过液态不混溶作用形成碳酸岩。然而,更加接近自然样品的多组分体系的实验均表明液态不混溶作用总是先于碳酸盐矿物分离结晶作用。因此,液态不混溶作用对关键金属成矿过程有着不可忽视的作用。尽管如此,已有不混溶实验表明当碳酸盐熔体和硅酸盐熔体发生不混溶之后,关键金属REE与Nb总是优先分配到硅酸盐熔体(碱性岩)中,但是在成矿杂岩体中,REE与Nb是高度富集在碳酸岩中。虽然不混溶实验表明REE与Nb在碳酸盐-硅酸盐熔体中的分配系数与含水量有关,即与熔体的聚合程度有关,但是绝大部分成矿碳酸岩成矿过程一般并不富水,所以碳酸岩中REE和Nb等关键金属元素超常富集的机理并不明确。因此未来的研究应重点关注在碳酸岩演化的过程中,除了水以外,其他配体对于关键金属元素在不混溶硅酸盐-碳酸盐熔体之间分配系数是否有影响,从而找到控制碳酸岩中关键金属成矿的关键。 相似文献
17.
Bjørn O. Mysen R. J. Arculus David H. Eggler 《Contributions to Mineralogy and Petrology》1975,53(4):227-239
Carbon dioxide solubilities in H2O-free hydrous silicate melts of natural andesite (CA), tholeiite (K 1921), and olivine nephelinite (OM1) compositions have been determined employing carbon-14 beta-track mapping techniques. The CO2 solubility increases with increasing pressure, temperature, and degree of silica-undersaturation of the silicate melt. At 1650° C, CO2 solubility in CA increases from 1.48±0.05 wt % at 15 kbar to 1.95±0.03 wt % at 30 kbar. The respective solubilities in OM1 are 3.41±0.08 wt % and 7.11±0.10 wt %. The CO2 solubility in K1921 is intermediate between those of CA and OM1 compositions. At lower temperatures, the CO2 contents of these silicate melts are lower, and the pressure dependence of the solubility is less pronounced. The presence of H2O also affects the CO2 solubility (20–30% more CO2 dissolves in hydrous than in H2O-free silicate melts); the solubility curves pass through an isothermal, isobaric maximum at an intermediate CO2/(CO2+H2O) composition of the volatile phase. Under conditions within the upper mantle where carbonate minerals are not stable and CO2 and H2O are present a vapor phase must exist. Because the solubility of CO2 in silicate melts is lower than that of H2O, volatiles must fractionate between the melt and vapor during partial melting of peridotite. Initial low-temperature melts will be more H2O-rich than later high-temperature melts, provided vapor is present during the melting. Published phase equilibrium data indicate that the compositional sequence of melts from peridotite +H2O+CO2 parent will be andesite-tholeiite-nephelinite with increasing temperature at a pressure of about 20 kbar. Examples of this sequence may be found in the Lesser Antilles and in the Indonesian Island Arcs. 相似文献
18.
花岗岩体系中岩浆阶段金属组分的浓度(英文) 总被引：2，自引：0，他引：2
E.N.GRAMENITSKIY 《地学前缘》2001,8(3):45-51
在岩浆阶段 ,富集金属元素最有效的机制是流体熔体的分离。受到硅酸盐熔体中盐的溶解度的限制 ,这种分离实为一个天然结晶过程的产物 ,所以必然发生在岩浆结晶的最后阶段。含氟的花岗岩体系中的矿物相的关系是已知的 ,并已确定了一个宽的液相不混溶区 ,其中也包括霞石标准分子的成分。该体系的不同部分 ,由多种元素在共存的硅酸盐和氟化铝两种熔体间的分配就可以得知。在这些实验中首次确定出元素分配与体系成分间的关系。这些数据也可解释一些经验数据所熟知的地球化学标志的变化。 相似文献
19.
Mathieu Roskosz Bjorn O. Mysen George D. Cody 《Geochimica et cosmochimica acta》2006,70(11):2902-2918
Solubility and speciation of nitrogen in silicate melts have been investigated between 1400 and 1700 °C and at pressures ranging from 10 to 30 kbar for six different binary alkali and alkaline-earth silicate liquids and a Ca-Mg-alumino silicate. Experiments were performed in a piston-cylinder apparatus. The nitrogen source is silver azide, which breaks down to Ag and molecular N2 below 300 °C. At high pressure and temperature, the nitrogen content may be as high as 0.7 wt% depending on the melt composition, pressure, and temperature. It increases with T, P and the polymerization state of the liquid. Characterization by Raman spectroscopy and 15N solid state MAS NMR indicates that nitrogen is not only physically dissolved as N2 within the melt structure like noble gases, but a fraction of nitrogen interacts strongly with the silicate network. The most likely nitrogen-bearing species that can account for Raman and NMR results is nitrosyl group. Solubility data follow an apparent Henry’s law behavior and are in good agreement with previous studies when the nitrosyl content is low. On the other hand, a significant departure from a Henry’s law behavior is observed for highly depolymerized melts, which contain more nitrosyl than polymerized melts. Possible solubility mechanisms are also discussed. Finally, a multi-variant empirical relation is given to predict the relative content of nitrosyl and molecular nitrogen as a function of P, T, and melt composition and structure. This complex speciation of nitrogen in melts under high pressure may have significant implication concerning crystal-melt partitioning of nitrogen as well as for potential elemental and isotopic fractionation of nitrogen in the deep Earth. 相似文献