Rare earth element diffusion in natural enstatite

Chemical diffusion coefficients of La, Nd, Eu, Gd, and Yb in natural enstatite have been measured at 850-1250 °C and 1 atm. Anhydrous diffusion experiments were run in Pt capsules in air, or in sealed silica glass capsules under an iron-wüstite (IW) solid buffer. The sources of diffusant were pre-reacted mixtures of synthetic enstatite powder and microcrystalline rare-earth aluminate garnet. Rutherford Backscattering Spectrometry (RBS) was used to measure diffusion profiles. For Gd diffusion in air over the temperature range 1000-1250 °C, the following Arrhenius relation is found for diffusion normal to (210):

     

石笋稀土元素含量的两种溶样方法测试结果对比分析

对于采自川东北诺水河溶洞群的石笋SJ3,采用2%的HNO3和HF+HNO3两种溶样方法分析测试了其稀土元素(REE)含量。结果表明:虽然多数石笋中存在碎屑物质,SJ3的少数样品在采用2%的HNO3溶解后有明显的残留物存在,但采用HF+HNO3全部溶解样品得到的SJ3的REE含量与采用稀HNO3溶样得到的结果并没有显著的差别。这表明SJ3的REE可能主要不是直接来自于地表土壤中难溶的硅酸盐矿物,而可能是土壤风化释放的REE通过吸附在颗粒/胶体态物质的表面,经过岩溶地下水的搬运而沉积到SJ3中。由此认为,采用稀酸溶样基本上可以将石笋SJ3的REE释放出来。      

Rare earth element fractionation in magmatic Ca-rich garnets

Igneous garnets have the potential to strongly fractionate rare earth elements (REE). Yet informations on partition coefficients are very scant, and criteria for distinguishing between hydrothermal and magmatic garnets are ambiguous. To fill this gap, we present trace element and isotopic data for two types of Ca-rich garnets from phonolites (Mt. Somma-Vesuvius). Both Ca-garnet populations are different in their style and dynamics of fractionation: one population is progressively strongly depleted in HREE from core to rim, reflecting REE fractionation in the host phonolite via earlier-crystallized garnets. Such examples for extreme changes in HREE in garnets are only known for hydrothermal grandites by REE-bearing fluids. The second garnet population is homogeneous and formed in a closed system. Near-flat patterns between Sm and Lu confirm experimental data indicating lower D(Sm)/D(Lu) for Ca-rich garnets than for e.g. pyrope-rich garnets. It follows: D ^Grt/PhMelt for La = 0.5, Sm = 48 and Yb = 110.     

Rare earth element zonation in Pacific ferromanganese nodules

The lower surfaces of ferromanganese nodules from the north equatorial Pacific Ocean, which are enriched in Mn, Cu and Ni, and the upper surfaces, which are enriched in Fe, P and Co, have been analyzed for La, Ce, Nd, Sm, Eu, Gd, Dy, Er and Yb. The REE contents are lower and the Ce anomaly is smaller in the lower surfaces than in the upper surfaces. The magnitude of the Ce anomaly increases with decreasing $\text{Mn}\text{Fe}$ ratio, indicative of a seawater origin. The zonal distribution of the other REE supports the conclusion derived previously from inter-nodule and nodule/sediment relationships that diagenetic fixation of rare earths in sediments affects their enrichment by nodular iron oxyhydroxides.     

Rare earth element and gallium diffusion in yttrium aluminum garnet

Diffusion of four rare-earth elements and gallium has been measured in yttrium aluminum garnet (YAG). Sources of diffusant were mixtures of alumina and rare-earth element oxides for REE diffusion, and mixtures of gallium and yttrium oxides for Ga diffusion. Diffusion profiles were measured with Rutherford backscattering spectrometry (RBS). For the rare-earth elements investigated, the following Arrhenius relations were obtained: D_La=6.87×10^–1 exp (–582±21 kJ mol^–1 /RT) m²s^–1 D_Nd=1.63×10^–1 exp (–567±15 kJ mol^–1 /RT) m²s^–1 D_Dy=2.70×10⁰ exp (–603±35 kJ mol^–1 /RT) m²s^–1 D_Yb=1.50×10^–2 exp (–540±26 kJ mol^–1 /RT) m²s^–1 Diffusion rates for the rare earths are quite similar, in contrast with trends noted for zircon. It is likely that these differences are a consequence of the relative ionic radii of the REE and the cations for which they substitute in the mineral lattice. For gallium, the following Arrhenius relation was determined: D_Ga=9.96×10^–6 exp (–404±19 kJ mol^–1 /RT) m²s^–1 Gallium diffuses faster than the REE in YAG and has a smaller activation energy for diffusion. These data mirror relative trends in diffusion rates for YIG, in which trivalent cations occupying tetrahedral and octahedral sites (i.e., Al, Ga, Fe) diffuse faster than trivalent cations occupying dodecahedral sites (i.e., Y and the REE), and suggest that the rate-limiting process in the diffusion-controlled regime of solid-state creep of YAG is the diffusion of yttrium. Received: 10 November 1997 / Revised; accepted: 13 March 1998     

Molecular modelling of rare earth element complexation in subduction zone fluids

Complexation of (trace) elements in fluids plays a critical role in determining element mobility in subduction zones, but to date, the atomic-scale processes controlling elemental solubilities are poorly understood. As a first step towards computer simulation of element complexation in subduction zone fluids, a thermodynamic cycle was developed to investigate the hydration environment and energetics of lanthanide complexes using density functional theory. The first solvation shell is explicitly defined and the remaining part of the aqueous fluid is modelled using a polarisable continuum model, which allows extrapolation to a broad pressure and temperature range.We illustrate our method by comparing solvation of lanthanide series elements in H₂O in the presence of fluoride or chloride for conditions relevant to subduction zones. The energetics of lanthanide- and lanthanide-fluoride/chloride hydration complexes were determined computationally. Calculated hydration free energies for trivalent lanthanides with explicit eight- and nine-fold coordinated first hydration shells show good agreement with literature data at room pressure and temperature. The hydration free energy is more negative for smaller complexes (heavy lanthanides) relative to larger complexes (light lanthanides), with the difference between La and Lu in water amounting to 361 kJ mol⁻¹. The hydration free energy of all lanthanide ions becomes less negative with increasing pressure (p) and temperature (T) up to 2.5 GPa and 1000 K (typical conditions in the upper part of subducting slabs). The free energy difference between light- and heavy-lanthanides remains essentially unchanged at elevated (p, T) conditions. There are minor geometrical differences in local hydration environment between light lanthanide-chloride (La-Nd) and heavy lanthanide-chloride (Pm-Lu) hydrated complexes, without a distinguishable energy difference. Complexation with fluoride is energetically more favourable than with chloride by 206 ± 4 kJ mol⁻¹ across the entire lanthanide series. The association of fluoride-water and chloride-water fragments with lanthanide-water complexes is energetically more favourable for aqueous lanthanide complexes surrounded by fewer first hydration shell water molecules.The methods developed in this study, in conjunction with simulation of the energetics of trace element incorporation into minerals, open the possibility to use molecular modelling to constrain elemental behaviour in subduction zones.     

Rare earth element distributions in a proto-stratiform ultramafic intrusion

Rare earth element (REE) abundances are reported for ten whole rock and eight mineral samples from the Preacher Creek ultramafic intrusion of southeastern Wyoming. Chondrite-normalized distribution patterns for the whole rocks exhibit a broad maximum between Sm and Gd and reflect the REE pattern of clinopyroxene, the major REE-bearing phase. Alteration of the primary mineral assemblages to actinolite and chlorite, which is generally minor, does not appear to have significantly affected the REE distributions. Absolute abundances of the REE in the rocks and constituent minerals increase as a function of differentiation, and relative abundances suggest an accompanying light REE enrichment. Trapped-liquid phases, which may be relatively enriched in REE, possibly account for some or all of the observed REE trends. The REE data, interpreted in terms of crystal-melt fractionation, suggest derivation of the intrusion by crystallization from a gabbroic magma having a REE distribution pattern similar to the parent magma of the Skaergaard stratiform complex. The results of this study are in accord with and complement a previous proposal that the Preacher Creek body formed in a manner analogous to major stratiform intrusions.     

Sorption of yttrium and rare earth elements by amorphous ferric hydroxide: Influence of solution complexation with carbonate

The influence of solution complexation on the sorption of yttrium and the rare earth elements (YREEs) by amorphous ferric hydroxide was investigated at 25 °C over a range of pH (4.0-7.1) and carbonate concentrations . Distribution coefficients, defined as , where [MS_i]_T is the total concentration of sorbed YREE, M_T is the total YREE concentration in solution, and [S_i] is the concentration of amorphous ferric hydroxide, initially increased in magnitude with increasing carbonate concentration, and then decreased. The initial increase of is due to sorption of YREE carbonate complexes , in addition to sorption of free YREE ions (M³⁺). The subsequent decrease of , which is more extensive for the heavy REEs, is due to the increasing intensity of YREE solution complexation by carbonate ions. The competition for YREEs between solution complexation and surface complexation was modeled via the equation:

     

Rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments

Analyses have been made of REE contents of a well-characterized suite of deep-sea (> 4000 m.) principally todorokite-bearing ferromanganese nodules and associated sediments from the Pacific Ocean. REE in nodules and their sediments are closely related: nodules with the largest positive Ce anomalies are found on sediments with the smallest negative Ce anomalies; in contrast, nodules with the highest contents of other rare earths (3 + REE) are found on sediments with the lowest 3 + REE contents and vice versa. ${}^{143}\text{Nd}{}^{144}\text{Nd}$ ratios in the nodules (～0.51244) point to an original seawater source but an identical ratio for sediments in combination with the REE patterns suggests that diagenetic reactions may transfer elements into the nodules. Analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to REE contents of nodules and sediments is negligible. Inter-element relationships and leaching tests suggest that REE contents are controlled by a P-rich phase with a REE pattern similar to that for biogenous apatite and an Fe-rich phase with a pattern the mirror image of that for sea water. It is proposed that 3 + REE concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate. Processes which favour the enrichment of transition metals in equatorial Pacific nodules favour the depletion of 3 + REE in nodules and enrichment of 3 + REE in associated sediments. In contrast, Ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions.     

Rare earth element mobility in the Roffna Gneiss,Switzerland

The Roffna Gneiss, a deformed Hercynian granite porphyry within the Penninic nappes of eastern Switzerland, underwent extreme cataclasis with the progressive development of phengite towards the margins of the nappe under conditions of the glaucophane schist to greenschist facies. This resulted in the selective mobilization of major and trace elements over distances of 10's to 100's of meters and the resetting of the Rb — Sr whole rock isotopic systems some 100 my ago. The component ratios and compositionvolume relationships of progressively deformed gneiss samples studied here suggest that this process was essentially isovolumetric. The mineralogy of the deformation sequence appears to have been controlled by a reaction involving the breakdown of microcline, albite and biotite and the formation of phengite and quartz. The fluids introduced Mg and H₂O, promoting the development of phengite, and removed the Na being released by the breakdown of albite. The fluids were most probably derived from the surrounding Triassic carbonates and quartzites. These relatively high fO₂ and carbonate rich fluids also introduced rare earth elements (REE) into the gneiss. The gneiss was progressively enriched in Eu up to 60%, Y up to 40%, and Yb up to 100%. These enrichments are associated with the development of epitaxial xenotime around zircon in the most phengite-rich sample. While the REE were mobile, uranium and thorium were essentially immobile. The formation of xenotime was suggested to explain the observed heavy REE enrichment when large differences in the REE contents were found for replicate analyses using HF and then lithium metaborate for dissolution. These differences arose because xenotime, like monazite, can be difficult (if not impossible) to dissolve in hydrofluoric acid. Due to the possibility of incomplete sample dissolution, we now recommend fusion with lithium metaborate for all REE, Lu — Hf or Sm — Nd studies.     

Rare earth element mobility in vesicular lava during low-grade metamorphism

A geochemical comparison of basaltic relicts and spilitic domains from two burial metamorphosed flows in central Chile, of similar original composition and rich and poor in amygdules, respectively, demonstrates a relationship between initial vesicularity and rare earth element (REE) mobility. During spilitization the REE were partly leached from permeable parts of the flows and precipitated in voids, now amygdules and veinlets. The REE (excluding Eu) moved coherently in the highly amygdaloidal flow: spilitic domains and amygdules inherited the basaltic REE pattern. Besides being characterized by a positive Eu anomaly, epidotes separated from amygdules have a REE distribution which mimics that of the basalt; the absolute contents range widely, suggesting local and/or temporal REE variations in the metamorphic fluids. Pumpellyite differs by being strongly enriched in heavy REE. Similar ratios of Th, Hf and Ta in samples as contrasting as relict basalt and a geode are consistent with coherent leaching. Coherent mobility, when established for a rock system, can be used to elucidate, for example, whether minerals in cross-cutting veins were formed by local redistribution or from introduced material.     

Rare earth element fractionation in metamorphogenic hydrothermal calcite,magnesite and siderite

Summary Normalized REE patterns of aqueous solutions and their precipitates bear information on the physico-chemical environments a fluid experienced during REE mobilization, fluid migration and minerogenesis. Positive Eu and Yb anomalies indicate REE mobilization by a F^–-, OH^–- and CO₃ ^2–-poor fluid in a high-temperature regime, but are only retained by a precipitating mineral if precipitation occurs in a low-temperature environment. Negative Ce anomalies are typical of oxidizing conditions and are unlikely to develop during siderite precipitation. LREE/HREE fractionation is controlled by fluid composition and mineralogical control. REE patterns of Ca minerals allow to class the reacting fluids in normal (Ca/ligand 1) and ligand-enriched (Ca/ligand 1), the latter being characteristic for remobilization processes.The Radenthein magnesite and Hüttenberg siderite deposits, both Carinthia, Austria, are discussed and shown to be of non-sedimentary, non-metamorphic, but metamorphogenic metasomatic origin.

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Fraktionierung der seltenen Erd-Elemente in metamorphogenen hydrothermoclen Calciten, Magnesiten und Sideriten

Zusammenfassung Normierte Lanthaniden-Verteilungsmuster wässeriger Lösungen und deren Präzipitate enthalten Informationen über die verschiedenen physiko-chemischen Bedingungen, denen die Fluidphase während der Mobilisierung der Lanthaniden, der Migration und der Minerogenese ausgesetzt war. Positive Eu- und Yb-Anomalien weisen auf eine Mobilisierung der Lanthaniden bei erhöhten Temperaturen durch eine F^–-, OH^–-und CO₃ ^2–-arme Lösung. Die positiven Anomalien der Lösung werden jedoch nur dann auf ein Mineral übertragen, wenn dessen Präzipitation in einem niedrigen Temperaturbereich erfolgt. Negative Ce-Anomalien sind Indikatoren oxischer Bedingungen, weshalb ihre Entwicklung im Verlauf einer Siderit-Präzipitation weitgehend ausgeschlossen werden kann. Die Fraktionierung von leichten und schweren Lanthaniden wird von der chemischen Zusammensetzung der Fluidphase und der mineralogischen Kontrolle bestimmt. Die Lanthaniden-Verteilungsmuster von Ca-Mineralen erlauben es, deren Mutter-Lösungen in normal (Ca/Liganil 1) und Liganden-reich (Ca/Liganil 1) zu untergliedern, wobei letztere für Remobilisierungsprozesse typisch sind.Verschiedene minerogenetische Modelle für Spatmagnesite aus der Lagerstätte Radenthein und Siderite aus der Lagerstätte Hüttenberg, beide Kärnten, Österreich, werden vor dem Hintergrund deren Lanthaniden-Verteilung diskutiert. Es wird gezeigt, daß sowohl für die Radenthein-Magnesite als auch für die Hüttenberg-Siderite nur ein nicht-sedimentäres, nicht-metamorphes, wohl aber metamorphogen-metasomatisches minerogenetisches Modell mit der Lanthaniden-Verteilung kompatibel ist.

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This paper was presented at the IGCP 291 Project Symposium Metamorphic Fluids and Mineral Deposits, ETH Zürich, March 2I–23,1991.     

Rare earth element patterns in Archean high-grade metasediments and their tectonic significance

Metasediments from two contrasting types of Archean high-grade terrains are interpreted as being derived from distinct tectonic settings. The Kapuskasing Structural Zone, Canada, represents the deep roots of a typical greenstone belt, whereas the Limpopo Province, southern Africa and Western Gneiss Terrain, Australia, mainly consist of shelf sediments deposited on a granitic basement and then buried to the depths required for granulite fades metamorphism. Upper amphibolite to granulite fades paragneisses from the Kapuskasing Structural Zone have REE patterns similar to those of greenstone belt sediments, except where partial melting has occurred, forming restites with Eu enrichment and melts with Eu depletion. Except in this latter instance, metamorphism has not affected the primary REE patterns. REE patterns in Archean upper amphibolite to granulite facies metasediments from the central Limpopo Province and Western Gneiss Terrain show wide differences, ranging from patterns which resemble those in post-Archean terrigenous sediments, to typical Archean sedimentary rock patterns. The diversity in REE patterns for these shallow shelf metasediments is interpreted as resulting from derivation from local provenances. Samples with “post-Archean” patterns, displaying Eu depletion, are interpreted as being derived from K-rich granitic plutons which were portions of small, stable early Archean terrains, precursors of the widespread late Archean-Proterozoic episode of major cratonic development.     

Rare earth element patterns in manganese nodules and micronodules from northwest Atlantic

The shale-normalized REE patterns of manganese nodules from the northwest Atlantic show enrichment in Sm and Eu relative to the heavier and lighter REE, excluding Ce, and are similar to the patterns previously observed in deep water (> 3000m) nodules from the Pacific. The inverse relation of this pattern to that of sea water and the high Ce anomaly (average 5.5) indicate that probably the REE in the nodules originate from sea water and the nodules are possibly hydrogenous. The patterns for micronodules are similar to those of the nodules but the concentrations of REE were substantially higher in two of them.The red clay occurring on abyssal hills where nodules and micronodules are found also shows higher REE concentrations over terrigenous gray clay. The latter is devoid of nodules and micronodules and occurs in abyssal plains. The excess REE in the red clay also show a pattern similar to those of the nodules and micronodules. Most of the micronodule samples show a lower Ce anomaly (1.7) and lower Co concentration compared to the nodules, so it is inferred that at least some micronodules were formed during post-depositional periods when the conditions were less oxidizing than average.     

Rare earth element partitioning between minerals from anhydrous spinel peridotite xenoliths

REE abundances in minerals from spinel peridotite xenoliths from West Germany, the south-western U.S. and Mongolia decrease in the order clinopyroxene > orthopyroxene > olivine > spinel. While clinopyroxenes are similar in absolute chondrite-normalized concentrations to those known from other studies, orthopyroxenes and olivines are significantly lower in LREE although comparable in HREE. Spinels are much lower in all REE than any previously reported values and are completely negligible for the REE budget of peridotites.Partition coefficients for most orthopyroxene/clinopyroxene pairs increase systematically from La to Lu. Olivine/clinopyroxene and spinel/clinopyroxene partition coefficients increase from the intermediate rare earth elements to Lu and normally are higher for La compared to Sm.The application of Nagasawa's (1966) elastic lattice model suggests that all heavy but only minor amounts of the light REE substitute into structural positions of orthopyroxene and olivine.Significant differences between orthopyroxene/clinopyroxene partition coefficients for various xenoliths may be assigned to dependences upon equilibration temperature and bulk chemistry.Apart from grain surface contaminations, fluid inclusions which are practically always present in mantle minerals, can highly concentrate light rare earth elements and thus may be responsible for unexpectedly high concentrations of incompatible elements frequently reported for mantle olivines or orthopyroxenes.     

Rare earth element distribution in Plio-Quaternary volcanic rocks from southern Peru

Rare-earth element abundances of calc-alkaline andesitic rocks from southern Peru show that these rocks cannot be produceed by a single stage process. The high content of LILE, particularly LREE requires their derivation from a source already enriched in these elements and having a distinctly fractionated REE pattern. It is suggested that ascending hydrous fluids, released from the subducted oceanic lithosphere, enriched the upper mantle in LILE by zone refining. The partial melting of such an enriched upper mantle, followed by fractional crystallization, could produce andesitic rocks. REE data indicate that shoshonitic rocks from southern Peru can be derived from an unfractionated garnet-bearing peridotite by a low degree of partial melting.     

Rare earth element geochemistry of the Fen alkaline complex,Norway

Determination of rare earth element (REE) abundances in rocks of the Fen complex has shown that within rocks of the first magmatic series REE abundances increase in the order urtiteFen magmas are discussed and it is considered that parental magmas had relatively high La/Yb ratios (40–60). Utilizing petrological evidence from other alkaline complexes coupled with experimental studies it is considered that the parental magma was a carbonated nephelinite produced by limited (<10%) partial melting of the mantle. All the Fen rocks are placed in a petrogentic scheme in which a carbonated nephelinite magma undergoes liquid immiscibility, differentiation and volatile transport.     

Rare earth element distributions among minerals in a granodiorite and their petrogenetic implications

A study of the distribution of lanthanide rare earths in a granodiorite from the eastern Peninsular Ranges batholith, southern California, reveals that a large fraction of the REE in this rock resides in the accessory phases sphene and allanite. The minerals plagioclase, alkali feldspar, biotite, epidote and apatite each contribute approximately 1% or less of each REE to the whole rock, with the exception of Eu for which plagioclase contributes 7%. Sphene and allanite together contain 80% to 95% of each REE. Each of these phases is zoned in REE concentration with substantial decreases from core to margin. Textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma. REE zoning trends in sphene and allanite, and unexpectedly low REE concentrations in largely later crystallizing minerals such as feldspar, indicate that the precipitation of sphene and allanite significantly reduced REE concentrations in residual melts. These results illustrate the potential that sphene and allanite have for controlling the behavior of REE in granitic magmas.Available information collectively suggest that the sampled granodiorite existed as a complete melt, that the REE contained in the assemblage of phases were derived by direct crystallization from the melt, and that the melt behaved essentially as a closed system once crystallization of the phases now present began. Close correspondences between the major and trace element chemistries of the granodiorite and phenocryst-poor lavas from similar tectonic settings support these conclusions. The REE pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism. The high liquidus temperature of a granodiorite melt (~ 1000°C) indicates the importance of mantle-derived components within the sources of batholithic magmas in the Peninsular Ranges.     

Rare earth element geochemistry and petrogenesis of miles (IIE) silicate inclusions

An ion probe study of rare earth element (REE) geochemistry of silicate inclusions in the Miles IIE iron meteorite was carried out. Individual mineral phases among inclusions have distinct REE patterns and abundances. Most silicate grains have homogeneous REE abundances but show considerable intergrain variations between inclusions. A few pyroxene grains display normal igneous REE zoning. Phosphates (whitlockite and apatite) are highly enriched in REEs (50 to 2000 × CI) with a relatively light rare earth element (LREE)-enriched REE pattern. They usually occurred near the interfaces between inclusions and Fe host. In Miles, albitic glasses exhibit two distinctive REE patterns: a highly fractionated LREE-enriched (CI normalized La/Sm ∼15) pattern with a large positive Eu anomaly and a relatively heavy rare earth element (HREE)-enriched pattern (CI-normalized Lu/Gd ∼4) with a positive Eu anomaly and a negative Yb anomaly. The glass is generally depleted in REEs relative to CI chondrites.The bulk REE abundances for each inclusion, calculated from modal abundances, vary widely, from relatively depleted in REEs (0.1 to 3 × CI) with a fractionated HREE-enriched pattern to highly enriched in REEs (10 to 100 × CI) with a relatively LREE-enriched pattern. The estimated whole rock REE abundances for Miles are at ∼ 10 × CI with a relatively LREE-enriched pattern. This implies that Miles silicates could represent the product of a low degree (∼10%) partial melting of a chondritic source. Phenocrysts of pyroxene in pyroxene-glassy inclusions were not in equilibrium with coexisting albitic glass and they could have crystallized from a parental melt with REEs of ∼ 10 × CI. Albitic glass appears to have formed by remelting of preexisting feldspar + pyroxene + tridymite assemblage. Yb anomaly played an important role in differentiation processes of Miles silicate inclusions; however, its origin remains unsolved.The REE data from this study suggest that Miles, like Colomera and Weekeroo Station, formed when a molten Fe ball collided on a differentiated silicate regolith near the surface of an asteroid. Silicate fragments were mixed with molten Fe by the impact. Heat from molten Fe caused localized melting of feldspar + pyroxene + tridymite assemblage. The inclusions remained isolated from one another during subsequent rapid cooling.     

云南大平掌铜多金属矿床稀土元素地球化学特征

滇西大平掌铜多金属矿床具典型的“双层结构”。对上部盆地相的块状硫化物和下部通道相的细脉浸染状硫化物的稀土元素分析表明,前者具正Eu异常的球粒陨石标准化配分模式,后者具负Eu异常的配分模式。这种变化与成矿流体演化有关。通过与大西洋中脊TAG热液活动区表层沉积硫化物和黑烟囱流体等的稀土元素配分模式对比,可以认为成矿是火山喷流沉积作用的结果。