The Carlisle Lakes-type chondrites: A new grouplet with high. Delta. sup 17 O and evidence for nebular oxidation

Journal Article · Sun Sep 01 00:00:00 EDT 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90380-N· OSTI ID:7206241

Weisberg, M K ^[1]; Prinz, M ^[2]; Kojima, Hideyasu; Yanai, Keizo ^[3]; Clayton, R N; Mayeda, T K ^[4]

---

1. American Museum of Natural History, New York, NY (United States) Brooklyn Coll., NY (United States)
2. American Museum of Natural History, New York, NY (United States)
3. National Inst. of Polar Research, Tokyo (Japan)
4. Univ. of Chicago, IL (United States)

Carlisle Lakes, ALH85151, and Y75302 are similar ungrouped chondrites which have petrologic and bulk compositional similarities to the ordinary chondrites, but are more oxidized; and their oxygen isotopic compositions differ. They represent a new grouplet which the authors call the Carlisle Lakes-type chondrites. They have the highest {Delta}{sup 17}O values (up to 2.91) measured to date. The whole chondrites and most of their chondrules plot on the same mass fractionation line on an oxygen 3-isotope diagram. They are olivine rich (>70 vol%), essentially metal free, and most olivine is FeO rich, equilibrated at Fa{sub 38}. Rare olivine and pyroxene grains in chondrules and fragments are zoned, and these are important in discerning the history of these chondrites. The zoning does not appear to have formed during crystallization from a melt droplet chondrule, but post-dated chondrule formation. Two hypotheses are postulated to explain the zoning: (1) parent-body thermal metamorphism and (2) nebular gas-solid exchange reactions accompanied by condensation of new FeO-rich olivine, utilizing existing olivine surfaces as nucleation sites. The occurrence of steep Fe-Mg compositional gradients of core-to-rim profiles, oscillatory zoning in olivine, fayalitic rims of Fa{sub 45} that exceed instead of approach the equilibrium composition of the matrix (Fa{sub 38}), and olivine-filled veins in zoned pyroxenes are more compatible with the nebular hypothesis. The Carlisle Lakes-type chondrites may have originally been derived from an ordinary chondrite-like precursor which was later oxidized, prior to its final lithification. However, the oxygen isotopic compositions of the whole chondrites and most of their chondrules suggest that the precursor probably formed in an oxygen isotopically distinct environment.

• OSTI ID: 7206241
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 55:9; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CHONDRITES
CHEMICAL COMPOSITION
MINERALOGY
CRYSTALLIZATION
GEOLOGIC HISTORY
ISOTOPE RATIO
NUCLEATION
OLIVINE
OXIDATION
OXYGEN 17
PETROLOGY
CHEMICAL REACTIONS
EVEN-ODD NUCLEI
GEOLOGY
ISOTOPES
LIGHT NUCLEI
METEORITES
MINERALS
NUCLEI
OXYGEN ISOTOPES
PHASE TRANSFORMATIONS
SILICATE MINERALS
STABLE ISOTOPES
STONE METEORITES
580000* - Geosciences