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高级变质岩中的熔体包裹体为包裹于寄主矿物（石榴子石、锆石等）中的熔体滴,主要由子晶矿物、玻璃和一些偶然捕获的固相矿物组成.最近10年来,熔体包裹体已经成为研究区域变质岩部分熔融作用的新手段和新途径.熔体包裹体粒径通常 < 20 μm,微小的尺度对熔体包裹体识别与分析提出巨大挑战.为此系统总结了熔体包裹体的识别方法、结构特征、化学成分分析方法,并指出熔体包裹体研究对于部分熔融的识别、部分熔融发生的温压条件、机制和流体状态的限定等具有重要的意义. 相似文献
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云南哀牢山和新疆可可托海伟晶岩矿物中熔融包裹体电子探针研究 总被引：5，自引：0，他引：5
运用电子探针测定了云南哀牢山伟晶岩和新疆可可 托海伟晶岩矿物中熔融包裹体及流体-熔融包裹体子矿物成分。据73个包裹体中120个测 点分 析结果,鉴定出锌尖晶石、刚玉、磷灰石、磁铁矿、白云母、黑云母、钾长石、钠长石、绿 柱石和石英等10种 子矿物,并确定矿物组合27个。其中锌尖晶石、刚玉在两地区伟晶岩熔融包裹体中属首次发 现,磷灰石成分属首次测定。两地伟晶岩矿物的熔融及流体-熔融包裹体中子 矿 物成分及矿物组合各异,包裹体中子矿物与主矿物的化学成分存在一定演化规律,可作为了 解伟晶岩浆结晶分异作用、元素演化规律的依据。研究表明,伟晶岩存在局部岩浆分异作 用,岩浆具不混溶性及非均匀性。此成果对了解伟晶岩物质成分、形成机制及成因研究具重 要意义。对岩浆岩、地幔岩及陨石研究也有一定启迪。 相似文献
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南极罗斯岛地区玄武岩中包裹体研究 总被引：1，自引：1，他引：1
南极罗斯岛玄武岩中分布着三种熔融包裹体(结晶质熔融包裹体、流体-熔融包裹体和玻璃质熔融包裹体)和CO_2流体包裹体。流体-熔融包裹体是一种新类型,它代表了从岩浆分异出热液的过程。本次研究中还发现了玄武岩浆的不混溶性,从而形成了富含K、Na和富含Fe、Mg的两种不同成分的岩浆。玄武岩中熔融包裹体的均一温度在1190—1350℃,其形成压力大于7.2—7.5 kbar。发现许多包裹体爆裂并有次生熔融包裹体形成,这证明玄武岩可能来自下地壳或上地幔。在这么深的地方形成的玄武岩浆分异出来的流体相主要是CO_2,而不是地壳中常见的H_2O,这对于了解上地幔、下地壳环境下可能存在的流体相方面有重要意义。 相似文献
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云南哀牢山和新疆可可托海伟晶岩矿物中熔融包裹体电子探针研究 总被引：6，自引：0，他引：6
运用电子探针测定了云南哀牢山伟晶岩和新疆可可 托海伟晶岩矿物中熔融包裹体及流体-熔融包裹体子矿物成分。据73个包裹体中120个测 点分 析结果,鉴定出锌尖晶石、刚玉、磷灰石、磁铁矿、白云母、黑云母、钾长石、钠长石、绿 柱石和石英等10种 子矿物,并确定矿物组合27个。其中锌尖晶石、刚玉在两地区伟晶岩熔融包裹体中属首次发 现,磷灰石成分属首次测定。两地伟晶岩矿物的熔融及流体-熔融包裹体中子 矿 物成分及矿物组合各异,包裹体中子矿物与主矿物的化学成分存在一定演化规律,可作为了 解伟晶岩浆结晶分异作用、元素演化规律的依据。研究表明,伟晶岩存在局部岩浆分异作 用,岩浆具不混溶性及非均匀性。此成果对了解伟晶岩物质成分、形成机制及成因研究具重 要意义。对岩浆岩、地幔岩及陨石研究也有一定启迪。 相似文献
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山东昌乐刚玉巨晶中的流体和熔融包裹体及其流体组分特征 总被引：7，自引：1，他引：7
山东昌乐第三纪玄武岩中产有刚玉巨晶,内含丰富的原生和假次生流体包裹体和熔融包裹体。流体包裹体可分为CO2单相包裹体、H2O-CO2两相和三相包裹体。熔融包裹体类型复杂,其中富流体相包裹体可分为含CO2收缩气泡两相熔融包裹体和气-液-固多相熔融包裹体。诸类包裹体主要赋含在刚玉晶核外的“主体”部分,以CO2单相流体包裹体和两相熔融包裹体最为发育,并且不同类型包裹体常密切伴生,表明它们形成时流体发生了不混溶作用:出现熔浆相(富含挥发分)、气相(CO2为主)和富水相(H2O-CO2为主)等多相体系。激光拉曼分析结果显示,各类包裹体中的气体组分主要是CO2,另有不等量的N2和H2S,据此划分为纯CO2、CO2-N2、CO2-H2S和CO2-N2-H2S等气体组合类型,没有发现O2、CH4和H2等组分。此外,拉曼分析也证实了流体包裹体和熔融包裹体中存在H2O。上述资料表明,昌乐地区深部流体以CO2为主,同时包含H2O、N2和H2S在内的多种组分,这些流体组分也是刚玉母浆系统的重要成分。 相似文献
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混合岩中浅色体的有限迁移及其对变形分解的影响 总被引：5，自引：0，他引：5
熔体在地壳和地幔中怎样迁移及其动力学是地质学中的一个重要问题。作为地壳深融作用的产物 ,混合岩中的浅色体提供了一个极好的机会来探讨影响地壳熔体在中下地壳迁移的因素。为此 ,我们对美国加州南 Sierra Nevada岩基中典型的混合岩、变泥质岩及邻近的花岗闪长岩进行了详细的主要元素地球化学和野外构造变形分析 ,同时应用流体动力学理论估算了在中下地壳条件下 ,典型浅色体的迁移距离。南 Sierra Nevada岩基中的混合岩中的浅色体厚度为 1mm至 1cm。在部分熔融程度较高的区域 (>10 % ) ,浅色体相互连接而成网结状构造 ,应变的承载方式主要以 IWL(Interconnected Weak L ayers)形式进行 ,即熔融体表现为弱相而承载大部分的应变。相反地 ,在部分熔融程度较低的区域 (<5 % ) ,浅色体孤立地出现 ,应变的承载方式主要以 L BF(L oad- Bearing Frame-work)形式进行 ,即应变主要由非熔融体的基质来承担。这表明在混合岩形成过程中 ,熔体的出现强烈地制约着应变分解作用。应用 Shaw的岩石粘度模型 ,我们根据浅色体的主要元素地球化学成分计算了浅色体在熔融状态下的粘度。根据流体动力学原理 ,估算了浅色体在不同条件下的迁移距离。计算结果表明 :1和典型花岗岩相比 ,浅色体具有较高的粘度 ,为 10 9～ 10 1 2 相似文献
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新疆乔尕山和粤西河台韧性剪切带金矿床中熔融包裹体的发现及矿床成因 总被引：6，自引：0，他引：6
乔尕山和河台金矿床属典型韧性剪切带金矿床，分别产于志留－泥盆系及震旦系云开群地层中。在2个矿床含金石英脉及糜棱岩中首次发现了熔融包裹体及流体－熔融包裹体，对解决此类型矿床成因具重大意义。乔尕山金矿床包裹体均一温度：熔融包裹体为900－1100℃，液相包裹体为285－390℃；河台金矿包裹体均一温度，熔融包裹体为870℃，不混熔液相包裹体为530℃，液相包裹体为180－350℃。前者流体性质属Na^ -K^ -Ca2 -SO4^2-HCO3^--Cl^-体系；后者流体性质属K^ -Ca^2 -Mg^2 -Na^ -SO4^2--HCO^3--Cl^-体系。运用电子显微镜能谱对熔融包裹体子矿物进行分析，鉴定出石英，钾长石、硅灰石及铝硅酸盐等9种子矿物，它们分别组成不同矿物组合，为熔融包裹体在矿脉中存在提供了重要的实验依据。在变质溶熔作用及强烈 动力变质作用下，沉积变质岩可以形成铝硅酸盐熔融体，具熔体－流体性质，成矿与多阶段铝硅酸盐熔体及流体作用相关。 相似文献
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George E. Sullivan 《Contributions to Mineralogy and Petrology》1991,106(3):296-308
The chemical compositions of melt inclusions in a primitive and an evolved basalt recovered from the mid-Atlantic ridge south
of the Kane Fracture Zone (23°–24°N) are determined. The melt inclusions are primitive in composition (0.633–0.747 molar Mg/(Mg+Fe2+), 1.01–0.68 wt% TiO2) and are comparable to other proposed parental magmas except in having higher Al2O3 and lower CaO. The primitive melt inclusion compositions indicate that the most primitive magmas erupted in this region are
not near primary magma compositions. Olivine and plagioclase microphenocrysts are close to exchange equilibrium with their
respective basalt glasses, whose compositions are displaced toward olivine from 1 atm three phase saturation. The most primitive
melt inclusion compositions are close to exchange equilibrium with the anorthitic cores of zoned plagioclases (An78.3-An83.1; the hosts for the melt inclusions in plagioclase) and with olivines more forsteritic (Fo89-Fo91) than the olivine microphenocrysts (the hosts for the melt inclusions in olivine). Xenocrystic olivine analyzed is Fo89 but contains no melt inclusions. These observations indicate that olivines have exchanged components with the melt after
melt inclusion entrapment, whereas plagioclase compositions have remained the same since melt inclusion entrapment. Common
denominator element ratio diagrams and oxide versus oxide variation diagrams show that the melt inclusion compositions, which
represent liquids higher along the liquid line of descent, are related to the glass compositions by the fractionation of olivine,
plagioclase and clinopyroxene (absent from the mincral assemblage), probably occurring at elevated pressures. A model is proposed
whereby clinopyroxene segregates from the melt at elevated pressures (to account for its absence in the erupted lavas that
have the chemical imprint of clinopyroxene fractionation). Zoned plagioclases in the erupted lavas are thought to be survivors
of decompressional melting during magma ascent. Since similar primitive melt inclusions occur in olivine microphenocrysts
and in the cores of zoned plagioclases, any model must account for all phases present. 相似文献
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We present melt and mineral compositions from nominally anhydrouspartial melting experiments at 2–3 GPa on a quartz eclogitecomposition (G2) similar to average oceanic crust. Near-soliduspartial melts at 3 GPa, determined with melt traps of vitreouscarbon spheres, have 55–57 wt % SiO2, rather less silicathan the dacitic compositions that are generally assumed fornear-solidus eclogite partial melts. At 2 GPa, equivalent near-soliduspartial melts are less silicic ( 相似文献
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This experimental study simulates the interaction of hotter, deeper hydrous mantle melts with shallower, cooler depleted mantle, a process that is expected to occur in the upper part of the mantle wedge. Hydrous reaction experiments (~6 wt% H2O in the melt) were conducted on three different ratios of a 1.6 GPa mantle melt and an overlying 1.2 GPa harzburgite from 1060 to 1260 °C. Reaction coefficients were calculated for each experiment to determine the effect of temperature and starting bulk composition on final melt compositions and crystallizing assemblages. The experiments used to construct the melt–wall rock model closely approached equilibrium and experienced <5% Fe loss or gain. Experiments that experienced higher extents of Fe loss were used to critically evaluate the practice of “correcting” for Fe loss by adding iron. At low ratios of melt/mantle (20:80 and 5:95), the crystallizing assemblages are dunites, harzburgites, and lherzolites (as a function of temperature). When the ratio of deeper melt to overlying mantle is 70:30, the crystallizing assemblage is a wehrlite. This shows that wehrlites, which are observed in ophiolites and mantle xenoliths, can be formed by large amounts of deeper melt fluxing though the mantle wedge during ascent. In all cases, orthopyroxene dissolves in the melt, and olivine crystallizes along with pyroxenes and spinel. The amount of reaction between deeper melts and overlying mantle, simulated here by the three starting compositions, imposes a strong influence on final melt compositions, particularly in terms of depletion. At the lowest melt/mantle ratios, the resulting melt is an extremely depleted Al-poor, high-Si andesite. As the fraction of melt to mantle increases, final melts resemble primitive basaltic andesites found in arcs globally. An important element ratio in mantle lherzolite composition, the Ca/Al ratio, can be significantly elevated through shallow mantle melt–wall rock reaction. Wall rock temperature is a key variable; over a span of <80 °C, reaction with deeper melt creates the entire range of mantle lithologies from a depleted dunite to a harzburgite to a refertilized lherzolite. Together, the experimental phase equilibria, melt compositions, and reaction coefficients provide a framework for understanding how melt–wall rock reaction occurs in the natural system during melt ascent in the mantle wedge. 相似文献
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Olivine-hosted melt inclusions have been analyzed from the young (4,150 ± 300 ybp) Dotsero basaltic (48.2 wt% SiO2) lava flow in Northwest Colorado, USA. Silicate melt-inclusion compositions have a bimodal distribution (41–46 wt% SiO2 and 47–50 wt% SiO2). Low-Si melt inclusions record high pre-eruptive sulfur concentrations (>1,000 ppm S) and variations in their major- and
trace-element compositions appears to be related to shallow assimilation of local basement sandstone. Whole-rock compositions
are modeled as a contamination of low-Si inclusion compositions with ~10 wt% sandstone. Host olivine crystallization may have
accompanied magma injection into a shallow storage chamber. In contrast to the low-Si melt inclusions, the high-Si population
is relatively degassed and records late-stage rapid crystallization either during or post-eruption. Hopper or skeletal olivine
grains in conjunction with the bimodal inclusion compositions suggest relatively rapid cooling rates at the time of eruption
and inclusion entrapment. Inclusion compositions, in conjunction with mineral textures, therefore provide a more complete
picture of shallow magma processes, coupling the relative timing of undercooling and crystallization, assimilation and melt
compositional evolution. Most of the inclusion and host textural and compositional data indicates late and very shallow petrogenetic
processes and does not appear to record deeper (mid-, lower-crustal) processes. 相似文献
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Pelitic hornfelses within the inner thermal aureole of the Etive igneous complex underwent limited partial melting, generating agmatic micro‐stromatic migmatites. In this study, observed volume proportions of vein leucosomes in the migmatites are compared with modelled melt volumes in an attempt to constrain the controls on melting processes. Petrogenetic modelling in the MnNCKFMASHT system was performed on the compositions of 15 analysed Etive pelite samples using THERMOCALC. Melt modes were calculated at 2.2 kbar (the estimated pressure in the southern Etive aureole) from solidus temperatures to 800 °C for both fluid‐absent and fluid‐present conditions. Volume changes accompanying fluid‐absent melting at 2.2 kbar were also calculated. P–T pseudosections reproduce the zonal sequence of the southern Etive aureole fairly well. The modelled solidus temperatures of silica‐rich pelitic compositions are close to 680 °C at 2.2 kbar and, in the absence of free fluid, melt modes in such compositions rise to between 12 and 29% at 800 °C, half of which is typically produced over the narrow reaction interval in which orthopyroxene first appears. Silica‐poor compositions have solidus temperatures of up to ～770 °C and yield <11.4% melt at 800 °C under fluid‐absent conditions. For conditions of excess H2O, modelled melt modes increase dramatically within ～13 °C of the solidus, in some cases to >60%; by 800 °C they range from 61 to 88% and from 29 to 74% in silica‐rich and silica‐poor compositions, respectively. Calculated volume changes for fluid‐absent melting are positive for all modelled compositions and reach 4.5% in some silica‐rich compositions by 800 °C. Orthopyroxene formation is accompanied by a volume increase of up to 1.48% over a temperature increase of as little as 2.7 °C, supporting the arguments for melt‐induced ‘hydrofracturing’ as a viable melt‐escape mechanism in low‐P metamorphism. Mineral assemblages in the innermost aureole support previous conclusions that partial melting took place predominantly under fluid‐absent conditions. However, vein leucosome proportions, estimated by image analysis, do not show the expected correlation with grade, and are locally greatly in excess of melt modes predicted by fluid‐absent models, particularly close to the melt‐in isograd. Melting of interlayered psammites, addition of H2O from interlayered melt‐free rocks, and metastable persistence of muscovite are ruled out as major causes of the excess melt anomaly. The most likely cause, we believe, is that local variations existed in the amount of fluid available at the onset of melting, promoted by focussing of fluid released by dehydration in the middle and outer aureole; however, some redistribution of melt by compaction‐driven flow through the vein channel network cannot be ruled out. The formation of melt‐filled fractures in the inner Etive aureole was assisted by stresses that caused extension at high angles to the igneous contact. The fractures were probably caused either by transient pressure reduction in the diorite magma chamber associated with a second phase of intrusion, or by sub‐solidus thermal contraction in the diorite pluton during the early stages of inner‐aureole cooling. 相似文献
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The study of melt microinclusions in olivine megacrysts from meimechites and alkali picrites of the Maimecha–Kotui alkali ultramafic and carbonatite province (Polar Siberia) revealed that the melt compositions corrected for loss of olivine due to post-entrapment crystallization of olivine on inclusion walls (differentiates of primary meimechite magma) match well to the composition of nephelinites and olivine melilitites belonging to carbonatite magmatic series. Modeling of fractional crystallization of meimechite magmas results in the high-alkali melt compositions corresponding to the silicate–carbonate liquid immiscibility field. The appearance of volatile-rich melts at the base of magma-generating plume systems at early stages of partial melting can be explained by extraction of incompatible elements including volatiles, by near-solidus melts at low degrees of partial melting, and meimechites are an example of such magmas. Subsequent accumulation of CO2 in the residual melt results in generation of carbonate magma. 相似文献
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An important control on magma rheology is the extent to which the magma crystallizes during ascent as a result of the effective undercooling created by volatile exsolution. To assess this undercooling, we need to know the final (anhydrous) one-atmosphere phase relations of silicic magmas. For this reason, we have performed one-atmosphere controlled-fO2 crystallization experiments on dacitic to rhyolitic melt compositions (67–78 wt% SiO2) and determined equilibrium phase assemblages, melt fractions, and some phase compositions over a range of temperatures. Experiments were run at oxygen fugacities between NNO+1 and NNO+2 and temperatures of 1,000 to 1,250°C. Constant phase compositions and sample crystallinities in runs longer than 3.5 days suggest that these runs closely approached compositional equilibrium. Additionally, melting experiments with similar compositions yielded results closely resembling those obtained in crystallization experiments. All samples have liquidus temperatures between 1,250 and 1,200 °C, with plagioclase the liquidus phase for the two most mafic samples and quartz for the most silicic sample. When associated glass compositions are projected into the Qz-Ab-Or system they define a revised one-atmosphere quartz-feldspar cotectic 5–10% less quartz normative than previously estimated. Glass compositions from each sample plot along this cotectic between 1,100 and 1,000 °C, consistent with the plagioclase-quartz co-crystallization textures found in runs at these temperatures. This cotectic constrains glass compositions to a maximum silica content of 76±1 wt% SiO2. Reported glass compositions in excess of 77 wt% SiO2 in volcanic samples suggest non-equilibrium crystallization, perhaps a consequence of large melt undercoolings.Editorial responsibility: I. Carmichael 相似文献
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In order to improve our understanding of HSE geochemistry, we evaluate the effect of Fe on the solubility of Pd in silicate melts. To date, experimentally determined Pd solubilities in silicate melt are only available for Fe-free anorthite-diopside eutectic compositions. Here we report experiments to study the solubility of Pd in a natural picritic melt as a function of pO2 at 1300 °C in a one atm furnace. Palladium concentrations in the run products were determined by laser-ablation-ICP-MS. Palladium increases from 1.07 ± 0.26 ppm at FMQ-2, to 306 ± 19 ppm at FMQ+6.6. At a relative pO2 of FMQ the slope in log Pd concentration vs. log pO2 space increases considerably, and Pd concentrations are elevated over those established for AnDi melt compositions. In the same pO2 range, ferric iron significantly increases relative to ferrous iron. Furthermore, at constant pO2 (FMQ+0.5) Pd concentrations significantly increase with increasing XFeO-total in the melt. Therefore, we consider ferric Fe to promote the formation of Pd2+ enhancing the solubility of Pd in the picrite melt significantly.The presence of FeO in the silicate melt has proven to be an important melt compositional parameter, and should be included and systematically investigated in future experimental studies, since most natural compositions have substantial FeO contents. 相似文献
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The effect of CaO and MgO, with or without TiO2 and P2O5, on the two-melt field in the simplified system Fe2SiO4–KAlSi3O8–SiO2 has been experimentally determined at 1,050°–1,240°C, 400 MPa. Despite the suppressing effect of MgO, CaO, and pressure on silicate melt immiscibility, our experiments show that this process is still viable at mid-crustal pressures when small amounts (0.6–2.0 wt%) of P2O5 and TiO2 are present. Our data stress that the major element partition coefficients between the two melts are highly correlated with the degree of polymerisation (nbo/t) of the SiO2-rich melt, whatever temperature, pressure, or exact composition. Experimental immiscible melt compositions in natural systems at 0.1 MPa from the literature (lunar and tholeiitic basalts) plot on similar but distinct curves compared to the simplified system. These relations between melt polymerisation and partition coefficients, which hold for a large range of compositions and fO2, are extended to various volcanic and plutonic rocks. This analysis strengthens the proposal that silicate melt immiscibility can be important in volcanic rocks of various compositions (from tholeiitic basalts to lamprophyres). However, the majority of proposed immiscible compositions in plutonic rocks are at least not coexisting melts, but may have suffered accumulation of early crystallized minerals. 相似文献
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Contributions to Mineralogy and Petrology - Melting experiments were performed in the systems at P H 2 O =5 kbars. The compositions of the plagioclases coexisting with melt or with melt and quartz... 相似文献