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钨、锡流-熔分配实验结果及其矿床成因意义 总被引：4，自引：1，他引：4
本文用实验确定了钨、锡在成分不同的花岗质熔体相与共存水热流体相的流-熔分配系数(D_(Me)~(V/L))及其与介质溶液(NaF,KF,HF,NaCl等水溶液)摩尔浓度间的函数关系。实验结果表明,钨、锡的分配行为明显不同。在相同条件下,随体系的不同,D_W~(V/L)比D_(Sn)~(V/L)大几倍至二十倍。钠和钾对钨、锡的流-熔分配行为的影响基本相同,而氟和氯对钨、锡的分配行为的影响相差甚远,花岗质熔体的主成分对D_W~(V/L)和D_(Sn)~(V/L)有复杂的影响。利用这些结果探讨与花岗岩有关的钨、锡矿床的成矿机理,得出了一些与前人不同的新认识。 相似文献
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F既是重要的岩浆挥发分,又是重要的助熔剂和矿化剂,同时也是克拉克值较大的元素之一,并且在(铝)硅酸盐熔体中高度可溶。本文从F的常见工业矿物和主要赋存形式、分配行为的多样性、对其它元素分配行为的影响、矿化作用(即亲氟元素在热液体系中的氟化物络合形式、存在环境和沉淀机制等)、萤石和冰晶石的溶解及沉淀机制以及富F岩浆一热液体系的成矿专属性及特征6个方面探讨了F的地球化学成矿作用。结论认为:F必须有能力大量进入与花岗质或伟晶岩质熔体共存的含水流体相中才具有进一步的成矿学意义,云英岩化、钠长石化、含黄玉—萤石石英脉、具有较高F/CaO比值的残余熔体以及F在高度演化花岗质岩浆中的过饱和等因素均可能导致含矿富F热液的出溶;但总体上,富F岩浆—热液体系具有成矿专属性的原因之一仍在于:F首先通过对熔体物理化学性质的影响间接支配着高场强亲氟元素如W、Sn、Nb、Ta、REE、U等的热液成矿效应。 相似文献
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再论富F熔体-溶液流体体系的成矿效应 总被引：1，自引：0，他引：1
通过例证的方式建立并诠释了富F熔体-溶液流体体系成矿效应的工作原理,认为:①F-OH-在不同载体矿物特别是云母类矿物中的置换行为构成了全岩F含量的主要贡献,具有物源意义;②在大多数情况下,F强烈倾向于分配进入晚期硅酸盐熔体相中,并深刻制约着熔体的结构、相平衡、物理化学性质和分异路径,不过在其他一些情况下F亦将大量进入热液或富水贫硅酸盐的"过渡性"流体相中;③富F流体体系另具有强烈萃取诸如W、Sn等高场强亲氟元素的成矿效应,最终可伴生萤石或冰晶石矿床,此时F作为矿化剂亦影响着Eh值、pH值和化学硬度等体系控矿因素。这样的三重作用围绕着F的基本化学性质一脉相承地促成了富F地质体系的成矿效应及其地球化学行为的特殊性。 相似文献
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实验研究了W、Sn、Be、Nb、Ta在不同压力(150 MPa、100MPa和50 MPa)、温度(850℃和800℃)条件下,于水饱和含P过铝质岩浆体系(P2O5分别为0.32%、1.98%、4.91%和7.78%)中流体-熔体间的分配.研究结果显示,W、Sn、Be、Nb、Ta在流体/熔体相间的分配系数Di＜0.1,表明它们强烈分配进入熔体相.W、Nb、Ta在流体/熔体相间的分配显示压力相关性随压力降低而降低. 相似文献
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硅酸盐熔体和流体中金的性质及行为研究进展 总被引：1，自引：0，他引：1
岩浆演化过程中岩浆—流体阶段发生的相转变过程控制了元素在两相之间的分配行为。作为与岩浆热液活动有密切成因联系的金矿床,其在硅酸盐熔体和流体中的性状及两相间的分配行为是控制该类矿床成矿的重要物理化学因素。介绍了金在流体、熔体中的性状,论述了其在流体/硅酸盐熔体间的分配行为不仅受温度、压力、氧逸度等物理化学条件的影响,还受流体组分(阴离子、阳离子)、熔体组成(Na2O+K2O/Al2O3,Na/K,SiO2,NBO/T)的制约;最后对目前实验研究存在的问题、改进方法以及今后的研究方向进行了探讨。 相似文献
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朱溪矿床是江南钨矿带中产于燕山期中酸性侵入岩与晚古生代碳酸盐岩接触带附近以矽卡岩矿体为主的钨铜矿床,发育“上铜下钨”的空间分带。浅部发育矽卡岩型和脉型铜矿体,深部发育矽卡岩型钨铜矿体、云英细脉-网脉型钨矿体及蚀变花岗岩型钨矿体。浅部矽卡岩型铜矿体中石榴子石U-Pb年龄为152.6±2.6 Ma、深部云英脉型钨矿体中白钨矿U-Pb年龄为153.4±2.2 Ma、深部矽卡岩型钨铜矿体中白钨矿U-Pb年龄为153.9±2.7 Ma,三者时代在误差范围内一致,表明钨、铜矿化均形成于同一热液体系,结合云英脉型钨矿体和矽卡岩型钨铜矿体中两类白钨矿的微量元素特征分析,流体起源于富WO42-、低Sr的高分异岩浆热液,白钨矿是以Ca2+空位的方式置换REE3+,稀土元素的分配行为记录了不同类型矿化流体性质。云英脉型钨矿化形成于还原环境,且氧逸度的显著降低以及围岩提供大量Ca2+促进了白钨矿的沉淀,而矽卡岩型钨铜矿化为相对开放的热液体系,后期经历了氧逸度升高,增强了流体富集金属Cu的能力,从而萃取... 相似文献
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《矿物岩石地球化学通报》2016,(3)
采用ICP-MS和ICP-OES分析了缅甸曼排钨矿床的花岗岩、云英岩和石英的微量元素和稀土元素组成。在对所获数据进行标准化处理和相关分析的基础上,将其与钨矿化地质特征进行综合分析研究,认为该区花岗岩体只形成钨矿床,而没有形成钨-锡矿床或锡-钨矿床的原因,很可能是在岩浆期后的气液作用过程中,W、Sn发生了矿化分离。W、Sn发生矿化分离的原因,除了与W、Sn元素的地球化学行为有关外,还与成矿热液系统的物质组成和富氧低硫的特性有关。 相似文献
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锡在花岗质熔体和流体中的性质及分配行为研究进展 总被引：2，自引：0，他引：2
元素在流/熔体间的交换、分配过程是岩浆热液矿床形成的重要环节，作为与岩浆活动有密切成因联系的典型矿种之一，锡在花岗质熔体和流体中的存在形式、分配行为及其影响因素是认识其成矿机理的关键。锡在花岗质熔体和流体中的分配特征不仅受温度、压力、氧逸度等条件的制约，流体组成和熔体的NBO/T（非桥氧键/桥氧键）、碱含量、AlK/Al(总碱与铝含量比)也是制约锡分配行为的重要因素；挥发分F、Cl对锡在流体、熔体中的地球化学行为影响尤为明显。 相似文献
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100MPa、800℃下Mo和W在流体／花岗质熔体相间分配的实验研究 总被引：3，自引：0，他引：3
利用“RQV-快速内冷淬火”（外加热冷封式）高温高压实验装置,在100MPa、800℃条件下,以东秦岭地区出露的高钾钙碱性岩浆岩（合峪花岗岩）为实验初始物,实验研究了Mo和W在花岗岩-H2O、花岗岩-NaCl（KCl）-H2O及花岗岩-NaF-H2O体系流体／熔体相间的分配行为。实验结果表明,Mo比W更倾向于分配进入流体相（DMo^流体/溶体〉〉DW^流体/溶体）,相对于纯水体系而言,流体介质中Cl和F的存在均有利于Mo和W向流体相迁移富集,随体系内Cl含量的不断增高,Mo和W的分配系数呈线性增大趋势,而在天然花岗岩可能含有的F含量范围之内,F含量的增高将阻碍Mo、W向流体相迁移,流体介质中Na／K（摩尔比）的变化对Mo和W的分配系数没有明显影响,表明体系碱质（Na或K）类型不是Mo和W在流体／熔体相间分配的主要影响因素。 相似文献
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Zircon (ZrSiO4) and hafnon (HfSiO4) solubilities in water-saturated granitic melts have been determined as a function of melt composition at 800° and 1035°C at 200 MPa. The solubilities of zircon and hafnon in metaluminous or peraluminous melts are orders of magnitude lower than in strongly peralkaline melt. Moreover, the molar ratio of zircon and hafnon solubility is a function of melt composition. Although the solubilities are nearly identical in peralkaline melts, zircon on a molar basis is up to five times more soluble than hafnon in peraluminous melts. Accordingly, calculated partition coefficients of Zr and Hf between zircon and melt are nearly equal for the peralkaline melts, whereas for metaluminous and peraluminous melts DHf/DZr for zircon is 0.5 to 0.2. Consequently, zircon fractionation will strongly decrease Zr/Hf in some granites, whereas it has little effect on the Zr/Hf ratio in alkaline melts or similar depolymerized melt compositions.The ratio of the molar solubilities of zircon and hafnon for a given melt composition, temperature, and pressure is proportional to the Hf/Zr activity coefficient ratio in the melt. The data imply that this ratio is nearly constant and probably close to unity for a wide range of peralkaline and similar depolymerized melts. However, it changes by a factor of two to five over a relatively small interval of melt compositions when a nearly fully polymerized melt structure is approached. For most ferromagnesian minerals in equilibrium with a depolymerized melt, DHf > DZr. Typical values of DHf/DZr range from 1.5 to 2.5 for clinopyroxene, amphibole, and titanite. Because of the change in the Hf/Zr activity ratio in the melt, the relative fractionation of Zr and Hf by these minerals will disappear or even be reversed when the melt composition approaches that of a metaluminous or peraluminous granite. It is thus not surprising that fractional crystallization of such granitic magmas leads to a decrease in Zr/Hf, whereas fractional crystallization of depolymerized melts tends to increase Zr/Hf. There is no need to invoke fluid metasomatism to explain these effects. Results demonstrate that for ions with identical charge and nearly identical radius, crystal chemistry does not alone determine relative compatibilities. Rather, the effect of changing activity coefficients in the melt may be comparable to or even larger than elastic strain effects in the crystal lattice. 相似文献
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This paper is focused on the role of boron coordination in determining the 11B/10B isotopic fractionation between melt/glass and biotite at magmatic temperatures. For this purpose, three evolved volcanic rocks from Roccastrada, Mt. Amiata, and Mt. Cimini belonging to the Neogene-Quaternary magmatism of central Italy were studied. In these samples, the measured boron biotite-glass partition coefficient ranges between 0.004 and 0.011, indicating that boron behaves as an incompatible element during biotite crystallization. The 11B magic-angle spinning nuclear magnetic resonance (NMR) spectra reveal the presence of trigonal BO3/2 units, tetrahedral BO4/2− sites, and three-coordinated BO2/2O− species containing one nonbridging oxygen. The relative contributions of these different boron sites were estimated by spectral deconvolution, and it was observed that the fraction of trigonally coordinated boron decreases with increasing K2O concentration in the glass. The 11B/10B isotopic fractionation between biotite and melt/glass was observed to be large even at magmatic temperatures and was found to be 1.0066 (Roccastrada sample), 1.00535 (Mt. Amiata sample), and 1.00279 (Mt. Cimini sample). Fractionation is mostly related to the relative amount of trigonal and tetrahedral boron sites in the glass network rather than to other processes, including the speciation of hydrous species in the glass structure. The measured α values are significantly higher than the calculated ones obtained using the reduced partition function ratios (RPFRs) for B(OH)3 and B(OH)4− as reported by Kakihana et al. (1977) and the abundance of trigonal and tetrahedral boron obtained by 11B NMR spectra. Furthermore, a nonlinear relationship is observed between the percentage of BO4 in the glass structure and the measured 1000lnα, suggesting that the approximation of monomeric B(OH)3 and B(OH)4− species contributions through ideal mixing in calculating the RPFRs in polyanions (Oi et al., 1989) probably does not apply to silicate glasses.The large B isotopic fractionation measured between glass and biotite and its dependence on the boron coordination in the glass are a limitation to the use of δ11B in the mineral to characterize magmas. Nonetheless, the high incompatible behavior of boron in the most common magmatic minerals rules out that fractional crystallization significantly modified the B isotopic composition of the melt. 相似文献
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Melt/peridotite interaction in the Southern Lanzo peridotite: Field, textural and geochemical evidence 总被引：2，自引：0，他引：2
This paper presents field, petrographic–structural and geochemical data on spinel and plagioclase peridotites from the southern domain of the Lanzo ophiolitic peridotite massif (Western Alps). Spinel lherzolites, harzburgites and dunites crop out at Mt. Arpone and Mt. Musinè. Field evidence indicates that pristine porphyroclastic spinel lherzolites are transformed to coarse granular spinel harzburgites, which are in turn overprinted by plagioclase peridotites, while strongly depleted spinel harzburgite and dunite bands and bodies replace the plagioclase peridotites. On the northern flank of Mt. Arpone, deformed, porphyroclastic (lithospheric) lherzolites, with diffuse pyroxenite banding, represent the oldest spinel-facies rocks. They show microstructures of a composite subsolidus evolution, suggesting provenance from deeper (asthenospheric) mantle levels and accretion to the lithosphere. These protoliths are locally transformed to coarse granular (reactive) spinel harzburgites and dunites, which show textures reminiscent of melt/rock reaction and geochemical characteristics suggesting that they are products of peridotite interaction with reactively percolating melts. Geochemical data and modelling suggest that <1–5% fractional melting of spinel-facies DMM produced the injected melts. Plagioclase peridotites are hybrid rocks resulting from pre-existing spinel peridotites and variable enrichment of plagioclase and micro-gabbroic material by percolating melts. The impregnating melts attained silica-saturation, as testified by widespread orthopyroxene replacement of olivine, during open system migration in the lithosphere. At Mt. Musinè, coarse granular spinel harzburgite and dunite bodies replace the plagioclase peridotites. Most of these replacive, refractory peridotites have interstitial magmatic clinopyroxene with trace element compositions in equilibrium with MORB, while some Cpx have REE-depleted patterns suggesting transient geochemical features of the migrating MORB-type melts, acquired by interaction with the ambient plagioclase peridotite. These replacive spinel harzburgite and dunite bodies are interpreted as channels exploited for focused and reactive migration of silica-undersaturated melts with aggregate MORB compositions. Such melts were unrelated to the silica-saturated melts that refertilized the pre-existing plagioclase peridotites. Finally, MORB melt migration occurred along open fractures, now recorded as gabbroic dikes.
Our data document the complexity of rock-types and mantle processes in the South Lanzo peridotite massif and describe a composite tectonic and magmatic scenario that is not consistent with the “asthenospheric scenario” proposed by previous authors. We envisage a “transitional scenario” in which extending subcontinental lithospheric mantle was strongly modified (both depleted and refertilized) by early melts with MORB-affinity formed by decompression partial melting of the upwelling asthenosphere, during pre-oceanic rifting and lithospheric thinning in the Ligurian Tethys realm. 相似文献
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Melt density and the average composition of basalt 总被引：9，自引：0，他引：9
Densities of residual liquids produced by low pressure fractionation of olivine-rich melts pass through a minimum when pyroxene and plagioclase joint the crystallization sequence. The observation that erupted basalt compositions cluster around the degree of fractionation from picritic liquids corresponding to the density minimum in the liquid line of descent may thus suggest that the earth's crust imposes a density filter on the liquids that pass through it, favoring the eruption of the light liquids at the density minimum over the eruption of denser more fractionated and less fractionated liquids. 相似文献
16.
Relationships between mineral/silicate melt partition coefficients and melt structure have been examined by combining Ca and Mn olivine/melt partitioning data with available melt structure information. Compositions were chosen so that melts with olivine on their liquidii range in degree of polymerization, NBO/T, from ∼0.5 to ∼2.5 under near isothermal conditions (1350-1400°C). Olivine/melt Ca-Mn exchange coefficients, Ca(olivine)/CaO(melt)/MnO(olivine)/MnO(melt) (KD Ca-Mnolivine/melt), as a function of melt NBO/T have a parabolic shape with a minimum KD Ca-Mnolivine/melt-value at NBO/T near 1. Notably, published KD Fe2+-Mgolivine/melt versus NBO/T functions are also parabolic with a maximum in KD Fe2+-Mgolivine/melt near 1 (Kushiro and Mysen, 2002).The olivine/melt partitioning data are modeled in terms of structural units (Qn-species) in the melt. The NBO/T-value corresponding to the minimum KD Ca-Mnolivine/melt is near that where the abundance ratio of Qn-species, XQ3/XQ2, has its largest value. Therefore, the activity coefficient ratio in the melt, γCa2+(melt)/γMn2+(melt), attains a minimum where the abundance ratio of XQ3/XQ2 is at maximum. It is inferred from this relationship that Ca2+ in the melts is dominantly bonded to nonbridging oxygen (Ca-NBO) in Q3-species, whereas Mn2+ is bonded to nonbridging oxygen (Mn-NBO) in less polymerized Qn-species such as Q2. 相似文献
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We use the results of elevated pressure melting experiments to constrain the role of melt/mantle reaction in the formation
of tholeiitic magma from Kilauea volcano, Hawaii. Trace element abundance data is commonly interpreted as evidence that Kilauea
tholeiite is produced by partial melting of garnet lherzolite. We experimentally determine the liquidus relations of a tightly
constrained estimate of primary tholeiite composition, and find that it is not in equilibrium on its liquidus with a garnet
lherzolite assemblage at any pressure. The composition is, however, cosaturated on its liquidus with olivine and orthopyroxene
at 1.4 GPa and 1425 °C, from which we infer that primary tholeiite is in equilibrium with harzburgite at lithospheric depths
beneath Kilauea. These results are consistent with our observation that tholeiite primary magmas have higher normative silica
contents than experimentally produced melts of garnet lherzolite. A model is presented whereby primary tholeiite forms via
a two-stage process. In the first stage, magmas are generated by melting of garnet lherzolite in a mantle plume. In the second
stage, the ascent and decompression of magmas causes them to react with harzburgite in the mantle by assimilating orthopyroxene
and crystallizing olivine. This reaction can produce typical tholeiite primary magmas from significantly less siliceous garnet
lherzolite melts, and is consistent with the shift in liquidus boundaries that accompanies decompression of an ascending magma.
We determine the proportion of reactants by major element mass balance. The ratio of mass assimilated to mass crystallized
(Ma/Mc) varies from 2.7 to 1.4, depending on the primary magma composition. We use an AFC calculation to model the effect of melt/harzburgite
reaction on melt rare earth and high field strength element abundances, and find that reaction dilutes, but does not significantly
fractionate, the abundances of these elements. Assuming olivine and orthopyroxene have similar heats of fusion, the Ma/Mc ratio indicates that reaction is endothermic. The additional thermal energy is supplied by the melt, which becomes superheated
during adiabatic ascent and can provide more thermal energy than required. Melt/harzburgite reaction likely occurs over a
range of depths, and we infer a mean depth of 42 km from our experimental results. This depth is well within the lithosphere
beneath Kilauea. Since geochemical evidence indicates that melt/harzburgite reaction likely occurs in the top of the Hawaiian
plume, the plume must be able to thin a significant portion of the lithosphere.
Received: 4 February 1997 / Accepted: 27 August 1997 相似文献
18.
T. G. Shumilova S. I. Isaenko B. A. Makeev A. A. Zubov S. N. Shanina Ye. M. Tropnikov A. M. Askhabov 《Doklady Earth Sciences》2018,480(1):595-598
Liquation structures were described in ultrahigh-pressure impact glasses of the Kara astrobleme (Pay-Khoy) with differentiation into the bisilica, aluminosilicate, and ore components for the first time. The sequence of differentiation of mineral phases upon solidification of an ultrahigh-pressure impact melt was established: coesite, silicate glass, augite, aluminosilicate glass of albite composition, and pyrite. The discovered impact glasses are highly resistant to postimpact alterations. 相似文献
19.
在流纹质岩浆中,存在两种不混溶的熔体,一种熔体富SiO_2贫FeO,另一种则相反。从熔体结构的角度看,前一种熔体富桥氧,后者则富自由氧。水的解聚作用可以改变流纹质岩浆的结构,即降低它的聚合程度,因此,含水流纹岩浆的粘度低于玄武岩浆的粘度,从而使流纹岩中流纹构造发育。 实际工作中应避免混淆流纹岩与酸性熔结凝灰岩。 相似文献
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