The Nakhla Martian meteorite is a cumulate igneous rock. Comment on “Glass-bearing inclusions in Nakhla (SNC meteorite) augite: heterogeneously trapped phases” (2001) by M. E. Varela, G. Kurat, and R. Clocchiatti

Summary ?All the properties of the Nakhla Martian meteorite suggest that it is a cumulate igneous rock, formed from a basaltic parental magma. Anomalous magmatic inclusions in Nakhla’s augite grains (Varela et al., 2001) can be explained by disequilibrium processes during crystal growth, and have little significance in the geological history of the meteorite. Received January 17, 2002; revised version accepted April 12, 2002     

Refractory inclusions in the Murchison meteorite

Mineralogical and petrographic studies of a wide variety of refractory objects from the Murchison C2 chondrite have revealed for the first time melilite-rich and feldspathoid-bearing inclusions in this meteorite, but none of these is identical to any inclusion yet found in Allende. Blue spinel-hibonite spherules have textures indicating that they were once molten, and thus their SiO₂-poor bulk composition requires that they were exposed to higher temperatures (>1550°C) than those deduced so far from any Allende inclusion. Melilite-rich inclusions are similar to Allende compact Type A's, but are more Al-, Ti-rich. One inclusion (MUCH-1) consists of a delicate radial aggregate of hibonite crystals surrounded by alteration products, and probably originated by direct condensation of hibonite from the solar nebular vapor. The sinuous, nodular and layered structures of another group of inclusions, spinel-pyroxene aggregates, suggest that these also originated by direct condensation from the solar nebular gas. Each type of inclusion is characterized by a different suite of alteration products and/or rim layers from all the other types, indicating modification of the inclusions in a wide range of different physico-chemical environments after their primary crystallization. All of these inclusions contain some iron-free rim phases. These could not have formed by reaction of the inclusions with fluids in the Murchison parent body because the latter would presumably have been very rich in oxidized iron. Other rim phases and alteration products could have formed at relatively low temperatures in the parent body, but some inclusions were not in the locations in which they were discovered when this took place. Some of these inclusions are too fragile to have been transported from one region to another in the parent body, indicating that low temperature alteration of these may have occurred in the solar nebula.     

Glass-bearing gabbro inclusions in hyaloclastites from Tindfjallajökull,Iceland

Gabbro inclusions from Tindfjallajökull are divided into two types: I. Panidiomorphic gabbros of non-cumulative origin composed of plagioclase + olivine ± clinopyroxene and interstitil vesicular glass. They have formed in equilibrium with the host magma and may either represent a marginal facies or a highly solidified magma body. In the latter case the host magma or part of it could be mobilized interstitial liquid. II. Allotriomorphic-hypidiomorphic tholeiitic olivine gabbro and diorite xenoliths with scarce Ti-pargasite which have undergone less than 10% partial melting in the host magma forming melts of alkali basaltic or Hekla andesite-like compositions dependent on the original mineral assemblage. Such liquids, enriched in K₂O and possibly other incompatible elements, may contaminate basaltic magmas rising slowly through a gabbroic lower crust. Large scale production of andesites by partial melting of such rocks is not possible but would need more hydrous or differentiated source rocks.     

Molybdenite in calcium-aluminum-rich inclusions in the Allende meteorite

The first observations of molybdenite in a meteorite have been made in two CaAl-rich inclusions in the Allende chondrite. The mineral occurs as single individuals completely enclosed in high Ni metal (62–64.5 wt. % Ni). The association with refractories is consistent with thermodynamic calculations which predict that Mo is a high temperature condensate even when nucleation constraints are imposed on the formation of a metal phase. Kinetic factors (including nucleation constraints) appear to have played an important role in the formation of molybdenite and the associated sulfides, magnetite and high nickel metal.     

Two forsterite-bearing FUN inclusions in the Allende meteorite

We have discovered two FUN inclusions, CG-14 and TE, among a group of five forsterite-rich inclusions in Allende, two of which are described for the first time herein. All five consist of euhedral forsterite and spinel crystals poikilitically enclosed by fassaite. Forsterite and spinel are usually segregated from one another, sometimes into a spinel-rich mantle and a forsterite-rich core. Some inclusions contain vesicles, indicating that they were once molten. The crystallization sequence inferred from textures is: spinel, forsterite, fassaite and, finally, Mg-rich melilite. One concentrically-zoned inclusion contains melilite in its mantle whose composition lies on the opposite side of the liquidus minimum in the melilite binary from that in its core. This suggests that segregation of forsterite from spinel in all of these inclusions could be due to volatilization of MgO and SiO₂ relative to Al₂O₃ and CaO from the outsides of droplets. CG-14 is relatively uniformly enriched in refractory elements relative to Cl chondrites by a factor similar to that for Ca-, Al-rich coarse-grained inclusions except for Ca, Al and Hf which are unusually low. No Ce anomaly such as found in FUN inclusions Cl and HAL is present in CG-14. Whole-rock samples of CG-14 and TE are more strongly mass-fractionated in oxygen relative to “normal” Allende inclusions than the FUN inclusion EK 1-4-1 and less so than Cl. Relative to bulk Allende, both inclusions have strongly massfractionated magnesium and silicon and ²⁵Mg excesses or deficits of ²⁴Mg or ²⁶Mg. CG-14 has a ²⁹Si excess or a deficit of ²⁸Si or ³⁰Si. Volatilization loss cannot be responsible for the magnesium and silicon isotope fractionations, as this would require prohibitively large mass loss from these magnesium-rich inclusions. The remarkable similarity in textures between FUN and non-FUN inclusions implies similar thermal histories, arguing against different rates of evaporative loss of major elements. Sputtering alone may be insufficient to account for the magnitude and direction of oxygen isotope fractionation in FUN inclusions.     

Accretionary rims on inclusions in the Allende meteorite

Many inclusions in Allende, particularly those with irregular shapes, are surrounded by a sequence of thin layers which differ from one another in texture, mineralogy and mineral-chemistry. The layer underlying all others contains either: IA, pyroxene needles + olivine + clumps of hedenbergite and andradite; IB, olivine doughnuts; or IC, rectangular olivine crystals. The next layer outward, II, contains tiny (<5 μm) olivine plates and Layer III large (5–10 μm) olivine laths. The final layer, IV, occurs as clumps of andradite + hedenbergite surrounded by magnesium-rich pyroxene needles. It separates Layer III from the Allende matrix which is more poorly sorted and more sulfide-rich than Layer III. Nepheline and iron sulfide are common constituents of most layers, the latter being particularly fine-grained and abundant in Layer II. Although not every layer is present on every inclusion, the sequence of layers is constant. Evidence that the rims are accretionary aggregates includes the presence of highly disequilibrium mineral assemblages and the fact that they are highly porous masses consisting of many euhedral crystals with few intergrowths. In addition, the layers are thickest in topographic hollows on the surfaces of inclusions and the inner layers are absent or discontinuous beyond such irregularities, suggesting that the probability of accretion of crystals was low initially, except in pockets, and became greater later, after a soft cushion of accreted condensate crystals had already formed. Separation of assemblages of different mineralogy, mineral-chemistry and texture into different rim layers seems best explained by nebular models in which long, slow cooling histories allow differentiation during condensation by grain/gas separation processes.     

Calcium-aluminum-rich inclusions in the Allende meteorite: evidence for a liquid origin

We have made a detailed examination of the mineralogy, textures and assemblages of six calcium-aluminum-rich inclusions (CAI) in the Allende meteorite. They can be classified into four types—hibonite-bearing, fassaite- and olivine-bearing, feldspathoid-bearing and fassaite-bearing CAI that are hibonite and olivine free. Examples of each type appear to have crystallized from a liquid rather than by agglomeration of solid nebular condensates. Some lines of evidence for a liquid origin are (1) the presence of spherical and ovoid shapes, (2) rims containing minerals (e.g. hibonite, perovskite) that are more refractory than minerals inside the inclusion, (3) eutectic and poikilitic textures, (4) minerals that are completely enclosed by more refractory minerals and (5) glass and fine-grained grossular stringers.Thermodynamic calculations and comparisons with liquidus phase diagrams indicate that the CAI could have been produced by direct condensation to metastable subcooled liquids that subsequently crystallized (blander and Katz, 1967) or by remelting of an equilibrium high-temperature condensate by impact. The diopside rims in some hibonite-bearing CAI and the paucity of metal in fassaite-olivinebearing CAI are more consistent with direct condensation of a liquid. The sluggishness of solid-solid reactions at the relatively high temperatures at which the CAI formed argues against assuming equilibrium in calculations at lower temperatures.     

Shaw meteorite: water-poor and water-rich melt inclusions in olivine and enstatite

Mineralogy and Petrology - During the petrological examination of a double polished thick section of the light-colored lithology of the Shaw meteorite, small melt inclusions, typically with...     

Refractory trace elements in Ca-Al-rich inclusions in the Allende meteorite

The condensation temperatures are calculated for a number of refractory trace metals from a gas of solar composition at 10^?3 and 10^?4 atm. total pressure. Instrumental neutron activation analysis of Ca-Al-rich inclusions in the Allende carbonaceous chondrite reveals enrichments of 22.8 ± 2.2 in the concentrations of Ir, Sc and the rare earths relative to Cl chondrites. Such enrichments cannot be due to magmatic differentiation processes because of the marked differences in chemical behavior between Ir and Sc, exhibited by their distributions in terrestrial igneous rocks and meteorites. All of these elements should have condensed from a cooling gas of solar composition above or within the range of condensation temperatures of the major mineral phases of the inclusions, which suggests that these inclusions are high-temperature condensates from the primitive solar nebula. Gas-dust fractionation of these materials may have been responsible for the depletion of refractory elements in the ordinary and enstatite chondrites relative to the carbonaceous chondrites.     

Mineralogy of silicate inclusions in the Elga IIE iron meteorite

The petrography, mineral modal data and major and trace element compositions of 15 silicate inclusions in the Elga iron meteorite (chemical group IIE) show that these inclusions represent chemically homogeneous zoned objects with highly variable structures, reflecting the sequence of crystallization of a silicate melt during cooling of the metal host. The outer zones of inclusions at the interface with their metal host have a relatively medium-grained hypocrystalline texture formed mainly by Cr-diopside and merrillite crystals embedded in high-silica glass, whereas the central zones have a fine-grained hypocrystalline texture. Merrillite appears first on the liquidus in the outer zones of the silicate inclusions. Na and REE concentrations in merrillite from the outer zones of inclusions suggest that it may have crystallized as α-merrillite in the temperature range of 1300–1700°С. Merrillite tends to preferentially accumulate Eu without Sr. Therefore, strongly fractionated REE patterns are not associated with prolonged differentiation of the silicate melt source but depend on crystallization conditions of Н-chondrite droplets in a metallic matrix. The systematic decrease in Mg# with increasing Fe/Mn in bronzite may indicate partial reduction of iron during crystallization of the inclusion melt. The modal and bulk compositions of silicate inclusions in the Elga meteorite, as well as the chemical composition of phases are consistent with the model equilibrium crystallization of a melt, corresponding to 25% partial melting of H-chondrite, and the crystallizing liquidus phase, merrillite, and subsequent quenching at about 1090°С. Despite a high alkali content of the average weighted bulk inclusion composition, La/Hf and Rb/Th fall within the field of H chondrites, suggesting their common source. Our results reveal that silicate inclusions in the Elga (IIE) iron meteorite originated by mixing of two impact melts, ordinary chondrite and Ni-rich iron with а IIE composition, which were produced by impact event under near-surface conditions on a partially differentiated parent asteroid.     

The Chassigny meteorite: a cumulate dunite with hydrous amphibole-bearing melt inclusions

The Chassigny meteorite is a moderately shocked olivine achondrite or chassignite with features indicative of a cumulate origin with some subsolidus annealing. Chassigny is an iron-rich dunite (Fo₆₈) with minor amounts of Ca-rich and Ca-poor pyroxene, alkalic feldspar, chromite, and melt inclusions in olivine. Accessory phases include chlorapatite, troilite, marcasite, kaersutite amphibole, pentlandite, ilmenite, rutile and baddeleyite. The meteorite experienced shock pressures of ~150–200 kbar as evidenced by planar and irregular fractures in olivine, local recrystallization in pyroxene and reduced birefringence and rare deformation lamallae in feldspar. Kaersutitic amphibole (K_0.05 Na_0.45)_0.50 (Ca_1.71 Na_0.29)_2.00 (Mg_2.73 ‘Fe’_1.19 Ti_0.73 A1_0.23 Cr_0.08 Mn_0.03)_4.99 (Si_6.05Al_1.95)_8.00 O₂₂ (OH, F)₂ containing hydrogen and lesser amounts of fluorine represents the first extraterrestrial occurrence of hydrous amphibole and the first meteoritic amphibole type other than fluorichterite. Kaersutite is found only in melt inclusions.Melt inclusion bulk compositional data suggest crystallization from a low-Ca melt that may have been similar in major element abundances to the silicate portion of LL group chondrites. However, Chassigny has a fractionated pattern for REE and the lack of metallic iron, possible presence of minor Ni in the olivine and Fe³⁺ in the chromites indicates that Chassigny formed under relatively more oxidizing conditions than most other achondrites. Therefore its parental melt could not have been directly derived from a chondritic composition in a simple single-stage process. The iron-rich bulk composition, cumulate texture and abundance as well as alkalic nature of the interstitial feldspar indicate that Chassigny could not have generated eucritic magmas. This places further constraints on its relationship to other meteorites and the parent body from which it is derived. The Brachina meteorite is similar to Chassigny except that it is finer grained, more feldspathic and is unshocked. It extends the fractionation range of this group which now represents two unusual meteorites.     

Carbon-bearing phases in shock-induced melt zones of the Elga meteorite

The mineralogy and texture of shock-induced melt veinlets and melt pockets in silicate inclusions in the Elga IIE iron meteorite have been studied by reflected-light optical microscopy, EMPA, SEM, Raman spectroscopy and TEM. The results suggest that Elga experienced two discrete impact events. The earlier event involved the collision of a metallic projectile with a silicate target and resulted in partial melting and recrystallization of the silicate material, forming schreibersite and oxide rims between the metal and silicate. The later impact event resulted in melt pockets in the silicate inclusions and was associated with fragmentation, melting, and brecciation of the rims and displacement of some fragments into the melt pockets. These fragments are shown to contain carbon-bearing phases: siderite and amorphous sp ² carbon, which form carbon–oxide, siderite–oxide, and siderite–schreibersite associations. The fact that the carbon-bearing fragments are spatially constrained to shock breccia and melt zones indicates that these fragments are genetically related to the impact process and that their carbon-bearing phases are of cosmic origin.     

Petrography and mineral chemistry of Ca-rich inclusions in the Allende meteorite

There are two types of white, coarse-grained, Ca-Al-rich inclusions in Allende. Type A inclusions contain 80–85 per cent melilite, 15–20 per cent spinel, 1–2 per cent perovskite and rare plagioclase, hibonite, wollastonite and grossularite. Clinopyroxene, if present, is restricted to thin rims around inclusions or cavities in their interiors. Type B inclusions contain 35–60 per cent pyroxene, 15–30 per cent spinel, 5–25 per cent plagioclase and 5–20 per cent melilite. The coarse pyroxene crystals in Type B's contain >15 per cent Al₂O₃ and >1.8 per cent Ti, some of which is trivalent. Type A pyroxenes contain <9 per cent Al₂O₃ and <0.7 per cent Ti.Electron microprobe analyses of 600 melilite, 39 pyroxene, 35 plagioelase, 33 spinel and 20 perovskite grains were performed in 16 Type A, 1 intermediate and 9 Type B inclusions in Allende and 1 Type A in Grosnaja. Melilite composition histograms from individual Type A inclusions are usually peaked between Ak10 and Ak30 and are 15–20 mole % wide while those from Type B inclusions are broader, unpeaked and displaced to higher åkermanite contents. Most pyroxenes contain < 1 per cent FeO. All plagioclase is An 98 to An 100. Spinel is almost pure MgAl₂O₄. Perovskite contains small (< 1 per cent) but significant amounts of Mg, Al, Fe, Y, Zr and Nb.Inferred bulk chemical compositions of Type A inclusions are rather close to those expected for high-temperature condensates. Those of Type B inclusions suggest slightly lower temperatures but their Ca/Al ratio seems less than the Type A's, indicating that the Type B's may not be their direct descendants. Some textural features suggest that the inclusions are primordial solid condensetes while others indicate that they may have been melted after condensation. Fragmentation and metamorphism may have also occurred after condensation.     

Ca-Al-rich inclusions from the Ningqiang meteorite: continuous assemblages of nebular condensates and genetic link to Type B inclusions

The petrography and mineral chemistry of 110 Ca-, Al-rich inclusions (CAIs) and 9 Ca- and/or Al-rich amoeboid olivine aggregates (AOAs) from the Ningqiang carbonaceous chondrite are reported. These CAIs are referred to as hibonite-bearing and hibonite-free melilite-spinel-rich (Type A), and spinel-pyroxene inclusions. Melilite is more gehlenitic in the hibonite-bearing Type As than in the other two types, and all of them vary within a range of Åk_0-30. Modal compositions of the three types of CAIs overlap with each other, and make up a continuum with wide ranges of melilite: spinel: diopside. The diopside occurs as rims on the CAIs or their individual concentric objects. The 9 AOAs contain spinel ± diopside ± anorthite in the centers of the aggregates; the spinel grains rimmed by diopside in the centers are similar to the spinel-pyroxene inclusions. Bulk compositions of these CAIs vary along the condensation trajectory, with the hibonite-bearing Type As plotting at the beginning followed by hibonite-free Type As then by spinel-pyroxene inclusions as temperature decreases. Bulk compositions of the AOAs are close to the lowest temperature condensation trajectory. Except for a few with compact textures, most of the Type As and spinel-pyroxene inclusions are fluffy aggregates, probably pristine vapor-solid condensates of the nebula.The bulk compositions of the Type As appear to overlap with the range of most melilite-Ti-Al-clinopyroxene-rich (Type B) inclusions. Hence, crystallization of liquids produced by melting the Type As can form Type B inclusions, without significant evaporative loss of MgO or SiO₂. A few Type Bs have bulk compositions deviating from the range of their proposed precursors, and may have suffered significant evaporation, as suggested in previous studies.     

Alteration of Al-rich inclusions inside amoeboid olivine aggregates in the Allende meteorite

Lightly altered Al-rich inclusions in amoeboid olivine aggregates have cores containing primary melilite + fassaite + spinel + perovskite and no secondary alteration products. In moderately altered inclusions, whose cores now contain only fassaite + spinel + perovskite, melilite was replaced by a fine-grained mixture of grossular + anorthite + feldspathoids and perovskite was partially replaced by ilmenite. In heavily altered inclusions, fassaite has been replaced by a mixture of phyllosilicates + ilmenite and the remaining primary phases are spinel ± perovskite. In very heavily altered inclusions, no primary phases remain, the spinel having reacted to form either phyllosilicates or a mixture of olivine + feldspathoids. This sequence of alteration reactions may reflect successively lower solar nebular equilibration temperatures. During alteration, SiO₂, Na₂O, K₂O, FeO, Cr₂O₃, H₂O and Cl were introduced into the inclusions and CaO was lost. MgO may have been lost during the melilite reaction and added during formation of phyllosilicates. Electron microprobe analyses indicate that the phyllosilicates are a mixture of Na-rich phlogopite and chlorite or Alrich serpentine. Thermodynamic calculations suggest that, at a solar nebular water fugacity of 10⁻⁶, Na-rich phlogopite could have formed from fassaite at ~470 K and chlorite from Na-rich phlogopite at ~328 K. Olivine mantling Al-rich inclusions is not serpentinized, suggesting that these objects stopped equilibrating with the nebular gas above 274 K.     

The microstructure of minerals in coarse-grained Ca-Al-rich inclusions from the Allende meteorite

The microstructure and microchemistry of minerals in Ca-Al-rich, coarse-grained inclusions (CAI) from the Allende meteorite have been investigated with transmission electron microscopy (TEM). Spinels contain only low to moderate dislocation densities and are characterized by a ubiquitous, fine black spotty texture believed to originate from a slightly non-stoichiometric composition. Ti-Al-pyroxenes are relatively featureless, but contain veins of secondary phases apparently deposited in unhealed cracks. Chromite has been identified in the veins, suggesting transport of oxidized iron during alteration. Melilites exhibit the greatest variety of microstructures and are the most heavily altered phase in CAI. High dislocation densities are common and crystals exhibit considerable internal strain, indicating that they have not been annealed. Alteration occurs both as veins along cracks and in fronts extending across several grains. Plagioclase is commonly twinned, but dislocations are rare. The size and morphology of antiphase domains suggest a high temperature of formation with significant low-temperature annealing. Submicron pyroxene precipitates are a ubiquitous and unusual feature of Allende plagioclase whose properties are most consistent with prolonged slow cooling and equilibration after plagioclase crystallization. The precipitates appear to be sufficiently abundant to contain the majority of Mg present in plagioclase but do not easily account for Na and Ti abundances. Wollastonite needles from a cavity in a “fluffy” Type A inclusion exhibit the growth habits and relatively perfect external surfaces indicative of direct condensation from a vapor. Alteration products are predominantly crystalline and alteration of melilite appears to have proceeded primarily by solid-state diffusion at a temperature of approximately 920°K. Overall, the TEM observations suggest that CAI formed under near equilibrium conditions characterized by slow cooling and that solid-state bulk diffusion was the major process affecting their post-crystallization history.     

Glass-bearing crustal xenoliths (buchites) erupted during the recent activity of Stromboli (Aeolian Islands)

Three xenoliths erupted as ejecta during recent violent explosion of Stromboli volcano (Aeolian Islands) were investigated in this paper. They consist of high-temperature mineral association (cordierite, hercynite spinels, sillimanite, ±plagioclase, ±mullite, ±corundum) and abundant glass (10–70 vol.%), and may be classified as buchites. The peraluminous composition of the xenoliths, their trace element distribution and REE patterns support their origin from granulite- and amphibolite-facies metapelites of the Calabrian continental crust, which is considered the crystalline basement beneath Stromboli. Buchites have an isotopic composition comparable to that of Stromboli extrusives and significantly different from that of the Calabrian basement.

The glass is generally colourless and has a Si–Al–alkali-rich composition, except for one sample where a Fe–Mg–Ca-rich reddish-brown glass also occurs. These two kinds of glass show complicated textures where patches of reddish-brown glass are often surrounded by plagioclase and/or cordierite or forms streaks and swirls with the colourless glass. Cordierite, plagioclase and oxides have different compositions according to their position in the xenoliths. Ca-rich plagioclase (An_72–95), Mg-poor cordierite (Mg-values 47–66) and Al-rich spinels are in the inner portions of the xenoliths and associated with colourless glass; on the contrary, close to the contact with the host lava or associated with coloured glass, cordierite shows higher Mg-values, Ti–Fe-bearing oxides occur and plagioclase is chemically similar to the basalt phenocrysts (An_66–71).

The abundant and fresh glass and the idiomorphic shape of the high-temperature minerals suggest that the xenoliths were hold in the basaltic magma, before its extrusion, for a significant time to allow their partial or nearly complete melting and subsequent nucleation and growth of new phases. During this stage, the interaction between the anatectic liquid and the basaltic magma affected the original isotopic composition of the xenoliths and, in some cases, produced glass and mineral phases (cordierite, plagioclase and oxides) with different composition.     

Trace elements in the Allende meteorite—III. Coarse-grained inclusions revisited

New RNAA determinations of Ba, Sr, Zr, U, Re, Pd, Ag, Zn and Se and INAA measurements of Lu are added to published data for 21 other elements in the same suite of ten samples. On the average, 21 refractory elements are not significantly fractionated from one another. The mean of their enrichment factors relative to Cl chondrites is 17.5 ± 0.4, indicating that the high-temperature condensate inclusions represent 5.7 wt% of the total condensable matter. Os, Ir, Ru, Re and most of the W condensed in one or more refractory siderophile element alloys along with small fractions of the Pd, Co, Au and Ag. The bulk of the Eu and Sr condensed in solid solution in melilite. Sc, Zr, Hf, Ta, U and the remaining REE condensed in a phase whose abundance in the inclusions is negatively correlated with that of melilite, either diopside or one or more minor or trace phases, including perovskite. Ba condensed in a different phase, separately from all these elements. In individual inclusions, fractionations are common between elements which were carried in by different condensate phases. Smaller fractionations are also observed for elements which condensed together. These may be due to variable proportions of them in a common condensate phase in response to different nebular equilibration temperatures or to multiple condensate phases containing different proportions of these elements. Available evidence indicates that some trace elements no longer reside in the phases which carried them into the inclusions, indicating a post-accretion thermal event which redistributed some of them. From the minimal variation of the Zr/Hf ratio in the inclusions, the solar system ratio is estimated to be 29.6 ± 1.8. From the mean U content of the inclusions and estimates of the bulk terrestrial and lunar U abundances, the Earth and Moon are estimated to contain 21% and 22–30% high-temperature condensates, respectively.     

Trace elements in the Allende meteorite—II. Fine-grained. Ca-rich inclusions

Nine fine-grained feldspathoid-, grossular-, spinel-, pyroxene-bearing inclusions from the Allende meteorite were analysed by instrumental neutron activation analysis. On the average, these inclusions are enriched in the refractory lithophile elements Ca, Sc, Ta and the rare earths by factors of 5–30 relative to Cl chondrites but are depleted in the refractory and volatile siderophiles, Ir, Co and Au. The volatile elements Fe, Cr and Zn are present at levels of 3.38–8.51%, 326–2516 ppm and 308–1376 ppm, respectively. Textural, mineralogical and chemical data suggest that the fine-grained inclusions formed in the solar nebula by the simultaneous condensation of volatiles and refractory lithophile elements which failed to condense into the coarse-grained, high-temperature condensate inclusions. The marked differences in the enrichment factors for different refractories in the fine-grained inclusions are caused by relatively small differences in their accretion efficiencies into the coarse-grained ones. The trace element data indicate that the refractories in the fine- and coarse-grained inclusions can only be the cosmic complements of one another if the fine-grained ones represent no more than ~ 20% of the most abundant refractory elements.