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

Barber, D. J.; Martin, Philip; Hutcheon, I. D.

doi:10.1016/0016-7037(84)90100-5

Cited by 35 publications

(29 citation statements)

References 34 publications

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“…We assume that this slight birefringence detected optically in the spinel grains stems from the non-relaxed elastic strain associated with differential thermal contraction which occurred during cooling from high temperature. We did not detect in the spinel phase any "fine black spotty texture" like the one reported by Barber et al (1984).…”

Section: Spinelcontrasting

confidence: 42%

Transmission electron microscopy of a refractory inclusion from the Allende meteorite: Anatomy of a pyroxene

Doukhan

Poirier

1991

Meteoritics

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Abstract-A crystal ofclinopyroxene from the coarse-grained refractory inclusion Egg6 of the Allende meteorite has been studied in detail by transmission electron microscopy.The pyroxene crystal contains euhedral, dislocation-free inclusions of pure spinel MgAlz04, without any topotactic relation to the host. Extensive dislocation walls at equilibrium, characteristic of high-temperature anneal, are present in the crystal. Alteration products are occasionally observed at the spinel-pyroxene interface close to regions where dislocation walls decorated with bubbles (or voids) are present. The bubbles, often in the shape oftubes along the dislocation lines, are thought to be due to the precipitation of a fluid migrating along the dislocations.The observations are compatible with crystallization of the refractory inclusions from the melt and with the existence of a later stage of metasomatism.

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Section: Spinelcontrasting

confidence: 42%

Transmission electron microscopy of a refractory inclusion from the Allende meteorite: Anatomy of a pyroxene

Doukhan

Poirier

1991

Meteoritics

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“…Alteration products in this and the inclusions described below typically consist of grossular, monticellite, wollastonite, aluminous diopside, nepheline and sodalite. In general, melilite is the only phase in Type B inclusions that underwent any significant alteration (MACPHERSON et al, 198 1;BARBER et al, 1984). Trace element data for this inclusion were reported by GROSSMAN and GANAPATHY (1976) and GROSSMAN et al (1977).…”

Section: Ts22mentioning

confidence: 97%

Fassaite composition trends during crystallization of Allende Type B refractory inclusion melts

Simon

Grossman

Davis

1991

Geochimica et Cosmochimica Acta

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Abstract-Fassaite is a major phase in Type B refractory inclusions and its wide compositional variability makes it an excellent recorder of crystallization-induced changes in liquid composition. Traverses across zoned crystals with electron and ion microprobes show that Ti, V, SC, Zr and Hf decrease from core to rim, while Mg, Si, REEs, and other trace elements increase. Fassaite/liquid distribution coefficients derived from the compositions of early f&ssaite and calculated parent liquid compositions are higher than previously reported fassaite Ds, e.g., 0.2-0.8 vs. 0.08-0.5 for the trivalent REEs, possibly due to the high Ti and Al contents of the fassaite we analyzed. Log-log plots of concentrations of elements vs. those of SC give linear relationships with slopes of (@'/" -l)/(@$ -l), where ni"/" .IS the bulk crystal/liquid distribution coefficient for element i. From this relationship, we derive effective fassaite/liquid Ds of 2.8 for SC, 1.5 for Hf, 1.1 for Zr, 0.52 for Y, 0.34 for Ta, 0.29 for Nb, and 0.3 l-O.48 for trivalent REEs. The effective Ds are applicable to fassaite crystallizing from melts having the compositions and thermal histories of Allende Type B refractory inclusions, and incorporate any equilibrium and kinetic effects that modify Ds during the course of crystallization. Observed fassaite REE contents can be reproduced by a fractional crystallization model in which the effective Ds are used. Tl '3+ is more compatible in fassaite than Ti4+ and, without equilibration of the residual liquid with an external reducing gas, Ti'+/Ti'"' ratios (where Tit" = Ti3+ + Ti4') should decrease from core to rim in fassaite crystals. Comparison of profiles of Ti3+/ Ti" ratios in several crystals with those calculated for fractional crystallization suggests that the trend in one crystal was controlled by fractional crystallization alone, but in two others the virtually constant Ti3+/Ti" ratios may imply that the liquids in these inclusions were able to maintain equilibrium with the solar nebular gas throughout crystallization. Attempts to determine the fo, of fassaite crystallization on the basis of Ti3'/Ti"' ratios must be based on fassaite grains which are not zoned with respect to Ti3+/ Ti'". The range of observed REE abundances in subliquidus fassaite (7-800 X Cl for La and 30-2000 X Cl for Lu) now encompasses those in grains previously identified as relict, removing a major reason for their identification as such. Rounded fassaite grains with fairly sharp Mg-rich rims and Ti-rich cores, poikilitically enclosed in mantle melilite in TS34 are candidates for relict grains. The grains are so Scrich that they would require extreme prior crystallization of spine1 and melilite, which is inconsistent with their very low REE contents (e.g., La at 3-7 X Cl). We suggest that the cores of these grains are relict and were trapped with liquid during formation of the mantle.

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“…Grossular has never been calculated to be a stable condensate in a cooling gas of solar composition. It does occur as an alteration phase in CAIs [12,29,30] and is calculated to be a stable condensate in Si-rich zones in supernovae [22,23] but in neither case is grossular ever in equilibrium with spinel. If type C inclusions originally consisted of grossular plus spinel, then they must either have formed under non-equilibrium conditions or in a non-solar environment.…”

Section: Determination Of Original Condensate Mineralogymentioning

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

Cited by 35 publications

References 34 publications

Transmission electron microscopy of a refractory inclusion from the Allende meteorite: Anatomy of a pyroxene

Transmission electron microscopy of a refractory inclusion from the Allende meteorite: Anatomy of a pyroxene

Fassaite composition trends during crystallization of Allende Type B refractory inclusion melts

The origin of type C inclusions from carbonaceous chondrites

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