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

Blander, M.; Fuchs, Louis H.

doi:10.1016/0016-7037(75)90083-6

Cited by 108 publications

(38 citation statements)

References 26 publications

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“…While Allende has been subject to young metamorphism, the introduction of halogens in the inclusions cannot be related to this event because of the presence of 129 Xe from 129 I decay (Podosek and Lewis, 1972]. Blander and Fuchs [ 1975] have discussed the importance of metastable condensation as a process in chondrule formation and have emphasized the importance of this process for the Allende chondrules. Wark and Lovering [ 1977] recently demonstrated the presence on Ca-Al rich chondrules of regular thin rims which are composed of distinct layers.…”

Section: Discussionmentioning

confidence: 99%

“…The 2 6 AI/ 2 7 AI requires that the higher temperature chondrules and the Fe-rich rims and aggregates condensed within less than I 0 5 years. For the interpretation of the 0 and Mg data we adopt the general point of view of Blander and Fuchs [ 1975] and hypothesize that metastable (supercooled) liquid droplets were present in the early solar nebula which contai~ed those el~ments associated with general equilibrium condensation over a Wide and somewhat variable temperature regime (1700-1200°K). This permits subsequent zoning by crystallization, and the presence of late high-temperature phases.…”

Section: Discussionmentioning

confidence: 99%

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correlated O And Mg isotopic anomalies in Allende Inclusions: II. Magnesium

Wasserburg¹,

Lee²,

Papanastassiou³

1977

Geophysical Research Letters

236

101

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Abstract. Mg in two Allende Ca-AI rich inclusions shows large isotopic, mass-dependent fractionation which enriched the heavier isotopes. After normalization, Mg in these inclusions shows negative 6 16 Mg which appears to require the presence of nuclear effects m Mg distinct from 16 AI decay. The Mg mass fractionation is correlated with distinct but smaller fractionation effects for 0 reported by Clayton and Mayeda for the same inclusions (see companion paper). The observation of distinctive but uniform Mg isotopic composition in different phases within single Allende inclusions indicates that nuclear effects in 0 and Mg are not due to the entrapment of interstellar carrier grains as discrete entities, which are preserved as remnants, but are instead due to a homogenized mixture of components of extraordinary isotopic composition mixed with a component of ordinary solar system material and subjected to isotopic fractionation. The distinct 0 isotopic composition of different phases Within a single inclusion is believed to be due to incomplete back-reaction of the higher temperature condensates with a cooler solar nebula of "normal" composition. The processes responsible for the 0 and Mg nuclear effects and the astrophysical site of their occurrence remain undefined.This note presents the observation in three Allende inclusions of large isotopic fractionation effects in Mg; two of the samples show a correlation between Mg and 0 isotopic anomalies and indicate possible nuclear effects in Mg. In general, the effect of small fractionation on the isotopic ratios of an element is given approximately by (1) where R, 1 is the measured ratio of the isotopes of mass Mi and Mi, R3 is the "normal unfractionated" ratio, and a is the fractionation factor per unit of mass difference which includes the fractionation intrinsic in the sample and that produced by the analytical procedures. A key issue is the ability to distinguish between fractionation in the sample and that produced by analytical procedures. We define any variation in Isotopic ratios which does not satisfy equation (I) as a non-linear isotopic effect. Catanzaro and Murphy [ 1966] showed that the Mg fractionation is less than l%o per mu (mass unit) in terrestrial samples. In a search for effects due to 2 6 AI, Schramm, Tera and Wasserburg [STW, 1970] studied Mg in a variety of samples using a technique with high precision and sensitivity. These workers normalized their data to a standard value of 2 5 Mgj2 4 Mg to determine a and corrected 2 6 Mg/ 2 4 Mg for fractionation using eq. (1) to obtain deviations in 2 6 Mg/ 2 4 Mg in permil relative to the standard. These arbitrarily normalized deviations are defined as 6 2 6 Mg. STW showed that there were no variations in 6 2 6 Mg within ± 0.2°bo and thereby demonstrated the absence of any non-linear effects in the samples investigated. In 1974 two independent groups [Gray and Compston, 1974; Lee and Papanastassiou (L & P), 1974] reported non-linear isotopic effects in Mg extracted from inclusions in the Allende...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

correlated O And Mg isotopic anomalies in Allende Inclusions: II. Magnesium

Wasserburg¹,

Lee²,

Papanastassiou³

1977

Geophysical Research Letters

236

101

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“…We do not know whether the N a that we observed is in solid solution in the anorthite as a part of its initial condensation composition or is in micron-scale late alteration products imbedded in the anorthite or has been otherwise introduced after initial condensation. Blander and Fuchs [1975] propose that the chondrules were formed by the condensation of a liquid representing metastable equilibrium with the solar nebula over a relatively wide effective temperature range, followed by crystallization of various phases from the melt; this model would allow the Nato be in solid solution with the anorthite from the time of crystallization.…”

Section: Discussionmentioning

confidence: 99%

Ion microprobe evidence for the presence of excess ²⁶Mg in an Allende anorthite crystal

Bradley¹,

Huneke²,

Wasserburg³

1978

J. Geophys. Res.

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An ion microprobe ha~ been. used to observe 28 Mg/"Mg in excess of normal values in anorthite crystals from Allende refractory mclus10ns. In one crystal, 28 Mg excesses up to 40% above normal, correlated with AI/Mg, were. obser_ved. These ~xc~sses are many times larger than those observed by other techniques. T_he _correla~10n with Al(Mg mdicated tha_t the excess '"Mg in the Allende anorthite is uniformly distributed m the anort~Ite. crystal. Analytical procedures and conditions were carefully controlled. Neverthel.ess, small but sig~Ifican~ apparent '"Mg/~fl:ig anomalies in isotopically normal samples were observed m analyses _by ?ne 10n microprobe. A repetition of the isotopic analyses using another ion probe produced normal ratios m the normal samples and confirmed large 28 Mg excesses in the Allende anorthite.

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“…All type C inclusions have "igneous" textures [3,[6][7][8] and were at least partially melted at some time during their history. If this melting event was primary, then type C inclusions formed as liquid condensates [3,6].…”

Section: Introductionmentioning

confidence: 99%

“…If this melting event was primary, then type C inclusions formed as liquid condensates [3,6]. If the melting event was secondary, then type C inclusions are re-melted condensates which may have undergone extensive volatilization.…”

Section: Introductionmentioning

confidence: 99%

The origin of type C inclusions from carbonaceous chondrites

Beckett

Grossman

1988

Earth and Planetary Science Letters

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Type C inclusions are plagioclase-rich, Ca-, Al-rich inclusions found in carbonaceous chondrites. They formed as solid condensates which were later melted in an event that destroyed the original condensate grains. Neither the melting event nor secondary alteration had a significant effect on bulk composition. Two stages in the condensation history can be discerned on the basis of major element bulk compositions. As in type A inclusions, the condensate phase assemblage originally consisted of melilite + spinel + perovskite + hibonite. Type C's were, however, significantly enriched in spinel relative to unaltered portions of most type A's. In contrast to type A's, condensate grains of spinel and melilite in type C's reacted partially with a coexisting gas to produce anorthite + diopside. One-half to two-thirds of the silica now in type C inclusions was introduced by this process. The reactions involving melilite and spinel that are predicted by equilibrium condensation calculations for a cooling gas of solar composition did not occur, probably due to kinetic constraints. Type C's may be related to Al-rich chondrules in ordinary chondrites by the addition of olivine and albite. Bulk compositions of Al-rich chondrules in enstatite chondrites are consistent with the addition of orthopyroxene and albite to type C inclusions. Thus, types A and C inclusions and Al-rich chondrules could represent sequences of condensates removed from interaction with the primitive solar nebula at progressively lower temperatures. If Al-rich chondrules represent the high-temperature component in chondritic material, then type C inclusions rather than the more common subgroups of CAIs could be the true parents of chondrites.

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

Cited by 108 publications

References 26 publications

correlated O And Mg isotopic anomalies in Allende Inclusions: II. Magnesium

correlated O And Mg isotopic anomalies in Allende Inclusions: II. Magnesium

Ion microprobe evidence for the presence of excess ²⁶Mg in an Allende anorthite crystal

The origin of type C inclusions from carbonaceous chondrites

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

Cited by 108 publications

References 26 publications

correlated O And Mg isotopic anomalies in Allende Inclusions: II. Magnesium

correlated O And Mg isotopic anomalies in Allende Inclusions: II. Magnesium

Ion microprobe evidence for the presence of excess 26Mg in an Allende anorthite crystal

The origin of type C inclusions from carbonaceous chondrites

Contact Info

Product

Resources

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Ion microprobe evidence for the presence of excess ²⁶Mg in an Allende anorthite crystal