Chemical, isotopic and mineralogical evidence for the origin of matrix in ordinary chondrites

Journal Article · Tue Aug 01 04:00:00 EDT 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90326-8· OSTI ID:7164342

Brearley, A J; Scott, E R.D.; Keil, K ^[1]; Clayton, R N; Mayeda, Toshiko K ^[2]; Boynton, W V; Hill, D H ^[3]

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1. Univ. of New Mexico, Albuquerque (USA)
2. Univ. of Chicago, IL (USA)
3. Univ. of Arizona, Tucson (USA)

The authors report the first combined chemical, isotopic and mineralogical study of fine-grained opaque matrix material from a type 3 ordinary chondrite, Allan hills A77299 (H3.7). Electron microprobe and instrumental neutron activation analysis of a large matrix lump show that is has a major element composition typical of matrix material in type 3 chondrites. Unlike chondrules, it shows no siderophile element depletions and is remarkably unfractionated relative to CI chondrites, suggesting that it is primitive solar system material. The matrix lump has an unique oxygen isotopic composition which lies below the terrestrial fractionation line and differs markedly from the composition of fine-grained matrix lumps and chondrule rims from Semarkona. Transmission electron microscope (TEM) studies of microtomed samples of the fine-grained fraction (<5 {mu}m) of the matrix lump show that is consists of rare, angular, clastic grains (>1 {mu}m) of pyroxene and olivine, embedded within a groundmass of rounded, fine-grained (<0.5 {mu}m) olivines. The authors conclude that the matrix lump in ALHA 77299 consists largely of material that formed by annealing of amorphous presolar dust or nebular condensates and could not have been derived from chondrules by any reasonable mechanism. However, the observed compositional differences between the matrix lump and chondrules in ordinary chondrites are consistent with the idea that some chondrules formed by melting of matrix-like material, accompanied by loss of siderophile and volatile elements.

• OSTI ID: 7164342
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 53:8; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
640107 -- Astrophysics &amp; Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
ACTIVATION ANALYSIS
CHEMICAL ANALYSIS
CHEMISTRY
CHONDRITES
ELEMENT ABUNDANCE
GEOCHEMISTRY
GEOLOGY
ISOTOPE RATIO
METEORITES
MICROANALYSIS
MINERALOGY
ORIGIN
PETROGENESIS
PETROLOGY
STONE METEORITES