Extraterrestrial water in micrometeorites and cosmic spherules from Antarctica: An ion microprobe study     

Ccile Engrand  Etienne DeLoule  Franois Robert  Michel Maurette  Gero Kurat 《Meteoritics & planetary science》1999,34(5):773-786

Abstract— The D/H ratios and water contents were measured by ion microprobe analysis in 52 individual Antarctic micrometeorites (AMMs) and 10 Antarctic cosmic spherules (ACSs) containing nuggets of iron hydroxide (COPS phase). In AMMs, δD values vary from ?366 to +249%‰ and water contents lie between 0.4-3.7 wt%. The COPS nuggets in cosmic spherules have high water contents (2 to 8 wt%) and exhibit δD values from ?144 to +167%‰, which is indicative of an extraterrestrial origin of their constituent water. The silicate portion of ACSs also contain extraterrestrial H equivalent to ～0.l to 1.2 wt% water. Deuterium-exchange experiments were performed with isotopically spiked water. These experiments demonstrate that water in mineral phases of AMMs and ACSs is indigenous and does not result from contamination during residence in Antarctic ice. The frequency distribution of D/H ratios in AMMs allows us to further narrow the relationship between AMMs and carbonaceous chondrites to CM and CI chondrites but contrasts with that of stratospheric interplanetary dust particles (IDPs) of similar sizes (from ?10 to 50 μm). The relatively narrow range of D/H ratios measured in AMMs as well as in ACSs (which are more resistant and thus less susceptible to collection biases) suggests that D-rich IDP-like particles are very rare in our AMMs collections. This indicates that these D-rich grains might constitute a minor fraction of the micrometeorite flux in the interplanetary medium and that possible collection biases in Antarctica would not be responsible for their strong depletion in the AMMs collections.  相似文献   

Aktashite Cu6Hg3As4S12 from the Aktash deposit, Altai, Russia: Refinement and crystal chemical analysis of the structure     

V. I. Vasil’ev  N. V. Pervukhina  S. V. Borisov  S. A. Magarill  D. Yu. Naumov  N. V. Kurat’eva 《Geology of Ore Deposits》2010,52(7):656-661

The composition and structure of aktashite from the Aktash deposit, Gorny Altai, Russia, have been studied by electron microprobe and X-ray structural analysis. On the basis of close compositions and crystal structures, the identity of aktashite from the Gal-Khaya and Aktash deposits has been demonstrated. Crystals of aktashite are of trigonal symmetry; the unit-cell dimensions are: a = 13.7500(4), c = 9.3600(3) Å, V = 532.54(8) ų, space group R3, Z = 3 for the composition of Cu₆Hg₃As₄S₁₂, R = 0.043. The structure of aktashite as a framework of vertex-shared HgS_4? and CuS_4? tetrahedrons of the same orientation is intimately related to the sphalerite-type structure. The earlier identified uncommon cluster group [As₄] has been verified and its parameters have been refined. It is shown that the structure may be represented as construction blocks (As₄S₁₂)_12? packed according to the law of the distorted cubic I-cell.  相似文献   

Buchbesprechungen     

E. Schroll  G. Kurat 《Mineralogy and Petrology》1980,27(3):231-232

Ohne Zusammenfassung  相似文献   

Chemistry of glass inclusions in olivines of the CR chondrites Renazzo, Acfer 182, and El Djouf 001     

Maria Eugenia Varela  Gero KuratPetter Hoppe  Franz Brandstätter 《Geochimica et cosmochimica acta》2002,66(9):1663-1679

Glass inclusions in olivines of the Renazzo, El Djouf 001, and Acfer 182 CR-type chondrites are chemically divers and can be classified into Al-rich, Al-poor, and Na-rich types. The chemical properties of the glasses are independent of the occurrence of the olivine (isolated or part of an aggregate or chondrule) and its composition. The glasses are silica-saturated (Al-rich) or oversaturated (Al-poor, 24% normative quartz). All glasses have chondritic CaO/Al₂O₃ ratios, unfractionated CI-normalized abundances of refractory trace elements and are depleted in moderately volatile and volatile elements. Thus the glasses are likely to be of a primitive condensate origin whose chemical composition has been established before chondrule formation and accretion, rather then the product of either crystal fractionation from chondrule melts or part melting of chondrules. Rare Na-rich glasses give evidence for elemental exchange between the glass and a vapor phase. Because they have Al₂O₃ contents and trace element abundances very similar to those of the Al-rich glasses, they likely were derived from the latter by Ca exchange (for Na) with the nebula. Elemental exchange reactions also have affected practically all olivines (e.g., exchange of Mg of olivine for Fe²⁺, Mn²⁺, and Cr³⁺). Glasses formed contemporaneously with the host olivine. As the most likely process for growing nonskeletal olivines from a vapor we consider the VLS (vapor-liquid-solid) growth process, or liquid-phase epitaxy. Glasses are the possible remnants of the liquid interface between growing crystal and the vapor. Such liquids can form stably or metastably in regions with enhanced oxygen fugacity as compared to that of a nebula of solar composition.  相似文献   

Petrology and geochemistry of peridotites and associated vein rocks of Zabargad Island,Red Sea,Egypt   总被引：2，自引：0，他引：2  

Prof. Dr. G. Kurat  Dr. H. Palme  Dr. A. Embey-Isztin  Prof. Dr. J. Touret  Dr. T. Ntaflos  Dr. B. Spettel  Dr. F. Brandstätten  Dr. C. Palme  Dr. G. Dreibus  Dr. M. Prinz 《Mineralogy and Petrology》1993,48(2-4):309-341

Summary Zabargad (St. John's) Island in the Red Sea contains three ultramafic bodies, one of which bas produced the famous gem olivine (peridot). The ultramafic rock types consist of two major groups—the peridotites and the vein rocks within them. The peridotites are divided into three groups: primitive, depleted and metasomatized. The primitive peridotites are the most abundant and are represented by mainly pristine spinellherzolites which have chemical compositions representative of the subcontinental upper mantle. The depleted peridotites are mainly harzburgites and nome dunites and both are similar to worldwide occurrences. The most depleted peridotites also appear to have the greatest metasomatic additions of incompatible elements, as has been noted at other localities. Metasomatic additions were clearly accompanied by tectonic shearing. Metasomatism included infiltration of incompatible elements and the formation of porphyroblasts of clinopyroxene, amphibole, Al-spinel and plagioclase; il took place under a variety of p-T conditions and with fluids of differing compositions.The vein rocks are mainly monomineralic and comprise olivinites, orthopyroxenites, clinopyroxenites, websterites, hornblendites and plagioclasites. These rocks are believed to have formed from fluids similar to that which metasomatized the host rock, rather than by some kind of igneous process. The fluids were derived from peridotite reservoirs (fertile and depleted) and apparently were in equilibrium with these reservoirs. Highly abundant fluid inclusions document the hypersaline and CO₂-dominated character of these fluids. Monomineralic vein rocks are closely associated with metasomatic and tectonic processes, and there is a complete transition between metasomatic impregnation and formation of vein rocks. These processes may have also been active in other peridotite bodies of the world, as was earlier recognized and documented in the Seiad Ultramafic Complex, California. Metasomatism is evident along clinopyroxenite and hornblendite veins, whereas orthopyroxenites, olivinites and plagioclasites do not show any interaction with the wall rocks. Olivinites are probably the latest (lowest p-T) vein rock type, and the latest olivine which formed within their open cavities became the gem peridot.Zabargad ultramafic rocks preserve relic phases indicating an initial depth of origin greater than 85 km. Clinopyroxenites preserve the memories of the highest p-T conditions and they may be the first vein rock type formed in the peridotites. The p-T path of uplift coincides with the oceanic geotherm at great depth but deviates systematically from it with falling pressure in a series of tectonic stages accompanied by metasomatism and recrystallization. The p-T and petrologic history indicates rapid uplift, a feature which is supported by extensive contact metamorphism of the associated metasediments.

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Petrologie und Geochemie der Peridotite und der mit diesen vergesellschafteten Ganggesteine der Insel Zabargad, Rotes Meer, Ägypten

Zusammenfassung Auf der Insel Zabargad (St.John's Island) im Roten Meer befinden sich drei Peridotit-Körper von denen einer seit Jahrtausenden den berühmten Peridot (Edelolivin) geliefert hat. Die ultramafischen Gesteine von Zabargad gliedern sich in zwei Hauptgruppen: die Peridotite und die mit diesen vergesellschafteten Ganggesteine. Die Peridotite können in drei Gruppen gegliedert werden: die primitiven, die verarmten und die metasomatisch veränderten Peridotite. Am meisten verbreitet auf Zabargad sind die primitiven Peridotite. Diese sind meist Spinell-Lherzolithe mit einer chemischen Zusammensetzung, welche dem subkontinentalen Oberen Erdmantel entspricht. Die verarmten Peridotite werden hauptsächlich von Harzburgiten und einigen wenigen Duniten repräsentiert. Beide sind jenen aus anderen Vorkommen der Welt sehr ähnlich. Die am stärksten verarmten Peridotite scheinen auch die stärksten metasomatischen Veränderungen erfahren zu haben—ein Trend, der auch schon an anderen ultramafischen Komplexen erkannt wurde. Metasomatische Anreicherungen inkompatibler Spurenelemente sind häufig direkt mit tektonischer Verformung und Kataklase gekoppelt. Die Metasomatose ist als Infiltration inkompatibler Elemente erkennbar und führte auch zur Bildung von Porphyroblasten von Klinopyroxen, Amphibol, Al-Spinell und Plagioklas. Diese Bildungen fanden unter verschiedenen p-T-Bedingungen statt und erfolgten durch Fluide mit unterschiedlichen Zusammensetzungen.Die (meist ultramafischen) Ganggesteine sind häufig monomineralisch und umfassen Olivinite, Orthopyroxenite, Klinopyroxenite, Websterite, Hornblendite und Plagioklasite. Wir glauben, daß diese Gesteine von Fluiden gebildet wurden, welche ähnlich jenen waren, die die Metasomatosen der Peridotite verursachten. Diese Genese wird von uns der magmatischen vorgezogen. Die Fluide stammten aus peridotitischen Reservoiren (fertilen und verarmten) und waren mit diesen offenbar im Gleichgewicht. Die Ganggesteine sind sehr reich an fluid inclusions, welche allerdings keine Flüssigkeit enthalten, sondern nur Festkörper (Salze) und CO₂ (± N₂), also einen trockenen, hypersalinen Charakter haben. Auch die monomineralischen Ganggesteine sind eng mit tektonischen Prozessen verknüpft und somit auch mit metasomatischen Prozessen. Es existieren vollkommene Übergänge von metasomatischen Imprägnationen bis zu echten Ganggesteinen. Solche Prozesse waren offensichtlich auch weltweit in anderen ultramafschen Komplexen aktiv und wurden schon im Seiad Ultramafc Complex in Kalifornien erkannt und beschrieben. Metasomatismus begleitet überlicherweise die Klinopyroxenit- und Hornblendit-Gänge. Orthopyroxenite, Olivinite und auch Plagioklasite zeigen jedoch keine Wechselwirkung mit den Wirtgesteinen. Olivinite sind wahrscheinlich die zuletzt gebildeten Ganggesteine. Der zuletzt sich bildende Olivin wurde der schönste und zum gesuchten Peridot.Alle ultramafschen Gesteine von Zabargad enthalten Minerale aus verschiedenen Bildungsepochen. Einige Relikte erinnern an eine Herkunft aus einer Tiefe von mehr als 85 km. Klinopyroxenite konservierten die höchsten p-T-Bedingungen. Sie waren daher wahrscheinlich die ersten (noch erhaltenen) Ganggesteine, welche sich im peridotitischen Erdmantel unterhalb des heutigen Roten Meeres bildeten. Der p-T-Pfad der Zabargad Ultramafitite deckt sich in großer Tiefe mit der ozeanischen Geotherme. Mit abnehmender Tiefe entfernt sich dieser Pfad allerdings zunehmend von der Geotherme und läßt eine Reihe von tektonischen Aktivitäten verbunden mit Metasomatose und Rekristallisation erkennen. Die p-T-Geschichte der Zabargad Ultramaftite deuten auf einen raschen Aufstieg aus dem Erdmantel hin. Diese Daten werden durch die weitverbreitete und intensive Kontaktmetamorphose der mit den Peridotiten assoziierten Metasedimenten unterstützt.

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Dedicated to Prof. Josef Zemann on the occasion of his 70th birthday

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With 12 Figures  相似文献   

D’Orbigny: A non-igneous angritic achondrite?     

G. Kurat  M.E. Varela  G. Weckwerth  H.W. Weber  E. Wäsch 《Geochimica et cosmochimica acta》2004,68(8):1901-1921

D’Orbigny is the sixth and by far the largest angrite known. Its bulk chemical and mineral chemical compositions, rare gas abundances and oxygen and rare gas isotope compositions fit the compositional ranges known from other angrites. It is, however, peculiar with respect to three features: the abundance of hollow shells, the presence of abundant open druses and the abundant presence of glasses.The shape, structure and texture of D’Orbigny and its mineral and bulk chemical compositions indicate an unusual genesis under changing redox conditions. In our view, data and observations are incompatible with an igneous origin of this rock but are suggestive of a complex growth and metasomatism scenario. The sequence of events apparently began with the formation of spheres of a phase which later vanished and therefore is unknown but could have been CaS. On top of these spheres (sizes from < 1-30 mm) olivine-anorthite intergrowths precipitated forming compact shells and fluffy protrusions. Aggregation of these objects plus occasional large plates made of the same intergrowths led to formation of a highly porous object with abundant large open space between the olivine-anorthite intergrowths. The aggregate also included previously formed olivines, olivinite rocks and Al-spinels. The latter carry highly porous decomposition rims of Cr-enriched Al-spinel and record mildly oxidizing conditions prevailing very early in D’Orbigny’s history. Conditions changed (with falling T?) and became oxidizing causing the phase(s) that constituted the spheres to become unstable. Their breakdown liberated large amounts of Ca and trace elements which at least in part re-precipitated by reacting with Si and Mg from the vapor to form augites that grew into the open space thus forming augite druses. Also, some of the preexisting olivine was converted into augite, which is very rich in refractory lithophile trace elements (abundances ∼ 10 × CI). Augites grew mainly under oxidizing conditions leading to atomic Fe/(Fe+Mg) ratios of about 0.44. Finally, conditions became highly oxidizing and strongly mobilized Ca from a source that apparently became unstable. The high partial pressures of Ca and Fe (and also Ti) led to precipitation of Ca-olivine and kirschsteinite (∼Fo1La20 and ∼Fo1La33, respectively) and of titaniferous aluminous hedenbergite—atomic Fe/(Fe+Mg) ∼ 0.97. Ulvöspinel and sulfides were also precipitated. Because the original phase(s) forming the early spheres vanished during these oxidizing events, the shells remained empty.In this scenario, D’Orbigny provides us with a record of changing conditions ranging from extremely reducing to highly oxidizing and with a record of the formation of an achondritic rock from a chondritic source. Angrites bear many similarities with CAIs, texturally, mineralogically and chemically. Possibly, they can be seen as CAIs, which grew larger than the ones we know from carbonaceous chondrites. Thus, angrites may bear a record of rare and special conditions in some part of the early solar nebula. They reproduce most of the textures and structures of CAIs: crystallized liquids (Asuka 881371, LEW 87051), metasomatic granoblastic rocks (LEW 86010, Angra dos Reis?) and aggregates (D’Orbigny). In addition, all angrites record metasomatic alterations, subsolidus processing after formation, also similar to what is recorded by most CAIs. Obviously, they missed the alkali metasomatic event recorded by many CAIs but they record a siderophile—lithophile element separation event that is not recorded by CAIs.  相似文献   

Chemical and crystallographic study of cronstedtite in the matrix of the Cochabamba (CM2) carbonaceous chondrite     

Dr. W. F. Müller  Dr. G. Kurat  A. Kracher 《Mineralogy and Petrology》1979,26(4):293-304

Summary The principal mineral component in the matrix of the Cochabamba carbonaceous chondrite is a phyllosilicate, which is identified as cronstedtite mainly on the basis of its chemical composition. Its approximate idealized formula is given by M₆ Fe _0.7 ³⁺ Al_0.5Si_2.7O₁₀ (OH)₈ with M=Fe²⁺, Fe³⁺, and Mg in somewhat variable amounts. TEM studies reveal the presence of three polytypes, and show a high degree of stacking disorder parallel to (001) with the displacement vector ±b/3 or ±2b . Crumpled amorphous masses in the matrix may contain structural building blocks of phyllosilicates. They, rather than the anhydrous minerals, seem to be the most likely progenitors of cronstedtite. Some constraints on its origin are reviewed. In addition to cronstedtite, observations on some other matrix phases are also reported.

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Chemische und kristallographische Untersuchung von Cronstedtit in der Matrix des kohligen Chondrits (CM2) Cochabamba

Zusammenfassung Der Hauptbestandteil der Matrix im kohligen Chondrit Cochabamba ist ein Schichtsilikat, das hauptsächlich aufgrund seiner chemischen Zusammensetzung als Cronstedtit identifiziert wurde. Die idealisierte Formel entspricht ungefähr M₆Fe _0.7 ⁺³ Al_0.5Si_2.7O₁₀(OH)₈ mit M=Fe²⁺, Fe³⁺ und Mg in wechselnden Mengen. TEM-Untersuchungen zeigen das Vorkommen von drei Modifikationen, sowie einen hohen Grad von Versetzungsfehlern parallel zu (001), mit dem Versetzungsfaktor ±b/3 oder ±2b/3. Deformierte amorphe Aggregate in der Matrix scheinen primitive Bausteine der Schichtsilikate zu sein. Sie (und nicht die wasserfreien Mineralien) dürften das Material darstellen, aus dem Cronstedtit gebildet wurde. Die Bildungsbedingungen von Cronstedtit werden diskutiert. Außerdem wird über Beobachtungen an anderen Matrixmineralien berichtet.

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With 4 Figures  相似文献   

Cryptic metasomatism in the upper mantle beneath Southeastern Austria: A laser ablation microprobe-ICP-MS study     

G. Dobosi  G. Kurat  G. A. Jenner  F. Brandstätter 《Mineralogy and Petrology》1999,67(3-4):143-161

Summary Upper mantle xenoliths from the classical location, Kapfenstein, Styria, as well as from Fehring, Styria, and Tobaj, Burgenland, have been analyzed by laser ablation microprobe inductively-coupled plasma mass spectrometry (LAM-ICP-MS). At all locations spinel lherzolite is the predominant xenolith type and thus our sample contains nine spinel lherzolites and only one harzburgite (from the richest location, Kapfenstein, sample Ka 167). All the rocks have protogranular to protogranular — porphyroclastic transitional textures. Mineral compositions are typical for fertile upper mantle rocks with 0.89 mg 0.92 for silicates and 0.10 cr 0.12 for spinel (0.18 for the harzburgite). The minerals are equilibrated with respect to major, minor and trace elements, except for clinopyroxenes in the sample from Tobaj (To 100) and one sample from Fehring (Feh 002) which have variable incompatible trace element contents.Trace element abundances are highest in clinopyroxene (3–4 × primitive mantle rare earth element — REEs — abundances) followed by orthopyroxene (about 0.5 × mantle REEs) and olivine (0.0005–0.05 × mantle REEs). Abundances of trace elements in all phases are usually correlated with their compatibility. The most incompatible elements (e.g., U, Th, Nb, Ta, La, Ce) are depleted with respect to the more compatible elements in three samples from Fehring and two from Kapfenstein. The remaining samples are enriched in either U, or U and Th, or the most incompatible REEs as compared to Nb and Ta which are usually depleted with respect to less incompatible elements. Clinopyroxenes of the sample from Tobaj (To 100) and one sample from Fehring (Feh 002) have variable U, Th, Nb and Ta contents. In sample Feh 002 this variation is accompanied by a correlated variation of the light REE contents and their abundances are also correlated with the closeness to the surface. The enrichments in U and Th are, however, not accompanied by any significant enrichment in Nb and Ta, the concentrations of which stay at low levels.The non-equilibrium trace element distribution in Clnopyroxenes suggests that the metasomatic events took place shortly before the rocks were delivered to the Earth's surface. Thus, metasomatism and volcanic activity seem to be related and a consequence of the rising diapir underneath the Pannonian Basin. Several metasomatic events probably related to fluids dominated by CO₂, water, or both were taking place. However, the intensity of that activity was generally low, as was the tectonic activity in the border zone of the Pannonian Basin. Only harzburgite Ka 167 provides evidence for some elevated activity of depletion and enrichment processes comparable to what has been found in the central region of the basin.

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Kryptische Metasomatose im Oberen Erdmantel unterhalb Südost-Österreich: eine Studie mittels Laser-Ablations-Mikrosonde-ICP-MS

Zusammenfassung Erdmantel-Xenolithe vom klassischen Vorkommen in Kapfenstein, Steiermark, und von Fehring, Steiermark, und Tobaj, Burgenland, wurden mittels Laser-Ablations-Mikrosonde-induktiv gekoppeltes Plasma-Massenspektrometer (LAM-ICP-MS) analysiert. An allen Lokalitäten dominieren Spinell-Lherzolithe die Xenolith — Population. Unsere Proben umfassen daher neun Spinell-Lherzolithe und nur einen Harzburgit (von der an Xenolithen reichsten Lokalität, Kapfenstein, Probe Ka 167). Alle Gesteine haben protogranulare bis protogranular-porphyroklastische Textur. Die Mineral-Zusammensetzungen sind typisch für fertile Gesteine aus dem Oberen Erdmantel mit 0,89 mg 0,92 in den Silikaten und 0,10 cr 0,12 im Spinell (0,18 im Harzburgit). Die Minerale sind hinsichtlich Haupt-, Neben- und Spurenelement-Verteilung im Gleichgewicht, ausgenommen die Klinopyroxene in der Probe von Tobay (To 100) und einer Probe von Fehring (Feh 002). Diese haben variable Gehalte an inkompatiblen Spurenelementen.Klinopyroxene haben die höchsten Spurenelement-Gehalte (3–4-fache Seltene-Erden-Element (SEE)-Gehalte des primitiven Erdmantels) gefolgt von Orthopyroxen (etwa 0,5-fache Erdmantel SEE) und Olivin (0,0005–0,005-fache Erdmantel SEE). Spurenelement-Häufigkeiten in allen Phasen sind üblicherweise mit ihrer Kompatibilität korreliert. In drei Proben von Fehring und zwei von Kapfenstein sind die inkompatibelsten Elemente (wie U, Th, Nb, Ta, La, Ce) gegenüber den etwas kompatibleren Elementen verarmt. Die übrigen Gesteine sind entweder an U, oder U und Th, oder den inkompatibelsten SEE relativ zu Nb und Ta angereichert. Die Letzteren sind üblicherweise relativ zu den weniger inkompatiblen Elementen verarmt. Klinopyroxene in der Probe von Tabaj (To 100) und einer Probe von Fehring (Feh 002) haben variable Gehalte an U, Th, Nb und Ta. Diese Variabilität ist in der Probe Feh 002 korreliert mit jener der Gehalte an leichten SEE und die Elementhäufigkeiten sind zusätzlich korreliert mit der Nähe zur Kornoberfläche. Die Anreicherungen an U und Th sind allerdings nicht von merklichen Anreicherungen an Nb und Ta begleitet, deren Häufigkeiten niedrig bleiben. Die unequilibrierte Spurenelementverteilung in den Klinopyroxenen deutet darauf hin, daß die Metasomatose kurz vor dem Transport der Gesteine an die Erdoberfläche stattfand. Metasomatose und vulkanische Aktivität scheinen daher verbunden und eisüdöstlichenne Konsequenz des unterhalb des Pannonischen Beckens aufsteigenden Erdmantel-Diapirs zu sein. Mehrere metasomatische Aktivitäten durch Fluide dominiert von CO₂, Wasser, oder beiden sind erkennbar. Die Intensität der Ereignisse war allerdings gering, vergleichbar der geringen tektonischen Aktivität in der Grenzzone des Pannonischen Beckens. Nur der Harzburgit Ka 167 zeigt Spuren intensiver Verarmungs- und Anreicherungs-Prozesse, die vergleichbar sind jenen, welche in der zentralen Region des Beckens die Erdmantel-Gesteine geprägt haben.

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With 5 Figures  相似文献   

Zoned CaAl-rich chondrule in Bali: New evidence against the primordial condensation model     

Gero Kurat  Georg Hoinkes  Kurt Fredriksson 《Earth and Planetary Science Letters》1975,26(2):140-144

One large (8.5 mm) chondrule in the Bali carbonaceous chondrite is strongly enriched in refractory elements similarily to the white objects in Allende which are widely believed to be “primitive” condensates. However, detailed investigations show the Bali chondrule to have an element distribution opposite to that predicted by the “primitive condensation” models. Refractory elements like Ti and Al are enriched at or near the surface of the chondrule. The contents of some volatile elements, e.g. Na, Si, and Cr, are higher in the central portion. It is suggested that this chondrule - and similar objects in other C-chondrites - originated in one, or more likely several, impact events and that the element distribution is the result of volatilization-condensation.  相似文献   

Geochemistry of ultramafic xenoliths from Kapfenstein,Austria: evidence for a variety of upper mantle processes     

G. Kurat  H. Palme  B. Spettel  Hildegard Baddenhausen  H. Hofmeister  Christl Palme  H. Wänke 《Geochimica et cosmochimica acta》1980,44(1):45-60

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