CARBON IN DARK INCLUSIONS OF THE ALLENDE METEORITE

Carbon contents of three Dark Inclusions (DI's) of the Allende meteorite, measured chemically, range from 0.56 to 1.17 weight %. When one includes the data reported by Bunch, Chang, and Ott (two DI's), the lower limit is 0.44%. The C-concentration map of a 1.6 × 1.6 mm² area straddling the boundary of a DI and matrix, or else of a DI and its dark halo, obtained with a ¹²C (d,p)¹³ C nuclear microprobe, shows that the C-content of the core of the DI is very uniform, and that the C-content of the rim is 2.9 ± 0.3 times larger. Variability of C-content of matrix and matrix-like areas of Allende appears to be the rule. DI's cannot be reworked bulk Allende, or precursor for bulk Allende without the addition, respectively removal of significant amounts of carbon. However, some Type 1 DI's might be reworked Allende matrix or precursor matter for that matrix.     

GAS RELEASE AND ORDERING OF CARBON IN THE ALLENDE METEORITE

Mass-spectrometric determinations of the inert gas release from samples of the Allende carbonaceous meteorite heated in the range 300°C to 1100°C, followed by Raman spectroscopic studies of the 1360 cm^?1 and 1580 cm^?1 bands of carbon support the hypothesis that the gas release at high temperatures is causally related with ordering of carbon.     

CONSTRAINTS ON CHONDRULE ORIGIN FROM PETROLOGY OF ISOTOPICALLY CHARACTERIZED CHONDRULES IN THE ALLENDE METEORITE

Petrographic and chemical features of Allende ferromagnesian chondrules previously analyzed for oxygen and silicon isotopes by Clayton et al. (1983a) provide additional information on chondrule origin. Allende, like other carbonaceous chondrites, contains two chondrule populations, but one of these is represented by only one chondrule in this isotopically characterized set. All Allende chondrules fall along an isotopic mixing line, probably defined by an ¹⁶O-rich solid component and an isotopically heavier oxygen gaseous exchange component. Differences in the amounts of isotopic exchange for porphyritic and barred chondrules presumably resulted from varying degrees of melting. Those porphyritic chondrules containing abundant relict grains experienced the least isotopic exchange. Chondrules with high bulk FeO/(FeO + MgO) ratios apparently persisted longer as liquids and contain more of the exchange component. The distinct directions of oxygen isotopic exchange in chondrules from carbonaceous, ordinary, and enstatite chondrites indicate that each formed from different solid precursor materials. Silicon isotopic variations in Allende chondrules probably reflect evaporative loss of lighter isotopes; however, silicon loss is also controlled by chondrule sizes, which are unknown. Observed correlations point to the importance of kinetic factors in a gaseous nebula for chondrule genesis, and are not consistent with models that explain chondrules as mixtures of several solids with distinct oxygen and silicon isotopic compositions.     

GROSSULAR IN THE ALLENDE (TYPE III CARBONACEOUS) METEORITE*

Grossular garnet has been observed in several white inclusions in the Allende meteorite. Compositions range from Gro_9sPy₅ to Gro₈₈Py₁₂ in five inclusions. Its mottled appearance indicates that it crystallized from a glass of near-grossular composition and not by a solid state reaction between wollastonite, anorthite and melilite. These grossular-bearing inclusions either condensed directly as metastable liquids from the solar nebula or if initial solid condensates were liquefied by some subsequent heating process. In either case, a prolonged residence time in a thermal blanket appears necessary to effect crystallization of the grossular.     

NEPHELINE AND SODALITE IN A BARRED OLIVINE CHONDRULE FROM THE ALLENDE METEORITE

Nepheline and sodalite have been found in association with glass in a barred olivine chondrule from the Allende C3V meteorite. The major minerals of the chondrule are olivine (Fo_80–88), bronzite (En₈₅Fs₁₂Wo₃), and chromite. Olivine bars are separated by glass of nearly pure plagioclase composition (An_81–99). Olivine composition is more Fe-rich than predicted by olivine-liquid equilibria (Fo₉₆). Conditions of non-equilibrium are implied from this and the presence of plagioclase glass and small amounts of subcalcic diopside (En₇₅Fs₁₂Wo₁₃) in the chondrule. The properties of this chondrule are consistent with liquid condensation, but melting of an amoeboid olivine aggregate or similar object could also have generated the chondrule-forming liquid. Nepheline and sodalite appear to have crystallized from this liquid under non-equilibrium conditions.     

THE COMPOSITION OF THE JOHNSTOWN METEORITE

A new analysis of the Johnstown meteorite, a hypersthene achondrite, gives the following results (weight percent): SiO₂ 53.48, TiO₂ 0.12, Al₂O₃ 1.43, Cr₂O₃ 0.83, FeO 15.63, MnO 0.54, MgO 25.87, CaO 1.40, Na₂O 0.04, K₂O 0.00, P₂O₅ 0.00, H₂O+ <0.1, H₂O- 0.05, Ni <0.05, Co <0.01, FeS 1.18, sum 100.57. Published and unpublished data on minor and trace elements in the bulk meteorite and in the pyroxene are presented in tabular form.     

THE COMPOSITION OF THE CHASSIGNY METEORITE

Spark source mass spectrometric analysis of the Chassigny meteorite has given the following data (in ppm): Rb 0.4, Sr 7.2, Y 0.64, Zr 1.5, Nb 0.32, Ba 7.1, La 0.39, Ce 1.12, Pr 0.13, Nd 0.54, Sm 0.11, Eu 0.038, Gd 0.11, Tb 0.02, Dy 0.12, Ho 0.03, Er 0.09, Yb 0.10, Pb 1.0, Th 0.057, U 0.021. These data, in conjunction with major element composition and mineralogical and textural features, indicate that this meteorite is an olivinerich cumulate, possibly genetically related to the nakhlites.     

THE MINERALOGY AND CHEMISTRY OF THE ALTA'AMEEM METEORITE

The Alta'ameem hypersthene chondrite is a light gray brecciated and metamorphosed meteorite composed mainly of olivine (27% Fa), orthopyroxene (24.5% Fs) and plagioclase (An¹⁰). Other minerals include troilite, kamacite, taenite, chromite, ilmenite, clinopyroxene, chalcopyrite, and apatite or merrillite. The mineralogical and chemical analyses suggest that the Alta'ameem meteorite belongs to the amphoterite group of chondrites. The chemical composition includes the following: Fe 3.39, Ni 1.13, Co 0.05, Cu 0.01, FeS 6.48, SiO₂ 39.48, TiO₂ 0.28, Al₂O₃ 2.25, FeO 16.46, MnO 0.40, MgO 25.66, CaO 1.47, Na₂O 1.05, K₂O 0.15, P₂O₅ 0.47, Cr₂O₃ 0.45; total 99.18.     

THE METEORITE CRATERS OF MORASKO IN POLAND

In 1914, in Morasko near Poznań, a 77.5 kg iron meteorite was found. Later there were additional findings. In 1955 seven crater-like structures, situated in the neighborhood of the meteorite finds, were identified. Until now it has been doubtful whether the iron meteorites and the craters belong together. New examinations by the author confirm beyond any doubt that the meteorites and the craters were caused by the same event.     

THE CHEMICAL COMPOSITION AND CLASSIFICATION OF THE KAROONDA METEORITE

New bulk compositional results are presented for the Karoonda meteorite which show that it is a member of the Vigarano type carbonaceous chondrites. Use of the petrographic symbol CK for Karoonda is shown to be unnecessary and inadvisable.     

THE ISOTOPIC COMPOSITION OF TELLURIUM IN THE ABEE METEORITE

Smith et al. (1978) measured the isotopic composition of tellurium in a number of whole rock meteorites by solid source spectrometry and concluded that all the data were identical to a terrestrial standard within experimental errors. However, Oliver et al. (1981) reexamined the data reported by Smith et al. (1978) and argued that, in the case of the Abee meteorite, a negative anomaly in ¹²⁴Te may be present, supporting the claim for a similar anomaly in Allende. The present work reports two sets of measurements of the tellurium isotopic composition of Abee, and compares the meteoritic data with a terrestrial tellurium standard. No isotopic anomalies can be distinguished within the error limits. However, further work on the isotopic composition of Te in residues from the Allende meteorite need to be pursued by accurate mass spectrometric analysis.     

THE HEDJAZ METEORITE

The Hedjaz meteorite has been studied in detail and on a chemical basis, with 22.1% total Fe, 9% metallic Fe, 1.3% Ni and constant olivine composition (Fa_23–24), can be classified as an L-group chondrite. However, petrographically Hedjaz is quite hoterogeneous and contains features characteristic of types 3, 4, 5, and 6, observations that refute a petrographic type classification. Indeed, Hedjaz, as a complex breccia, exhibits no evidence of metamorphic equilibration after accretion and supports the contention that type 4 (also 5 and 6) chondrites are not derivatives of type 3 material, and that types 5 and 6 are not necessarily more “metamorphosed,” only better crystallized.     

THE LANDES METEORITE

The Landes silicate-bearing octahedrite is a new find from Grant County, West Virginia. Minerals and their compositions are very similar to those in Odessa-type silicate inclusions. The angular nature of the inclusions, recrystallization textures, and mineral compositions indicate a “xenolithic” origin for the inclusions.