16O excesses in olivine inclusions in yamato-86009 and murchison chondrites and their relation to CAIs

Science

Volumn 283, Issue 5403, 1999, Pages 828-831

  Hiyagon, Hajime ^a   Hashimoto, Akihiko ^b  

^a UNIVERSITY OF TOKYO   (Japan)

^b HOKKAIDO UNIVERSITY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

ISOTOPE; OXYGEN; ALUMINUM; CALCIUM; IRON DERIVATIVE; MAGNESIUM DERIVATIVE; OLIVINE; SILICATE;

CHONDRITE; OLIVINE;

ARTICLE; ASTRONOMY; CHEMICAL ANALYSIS; MICROANALYSIS; OXYGEN CONCENTRATION; PRIORITY JOURNAL; QUANTUM CHEMISTRY;

ALUMINUM; CALCIUM; IRON COMPOUNDS; MAGNESIUM COMPOUNDS; METEOROIDS; OXYGEN; OXYGEN ISOTOPES; SILICATES;

EID: 0033524499     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.283.5403.828     Document Type: Article

References (36)

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11. 18O down to ∼-10‰ from an ordinary chondrite julesburg.
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13. 18O = +4.70‰ [I. Jabeen, M. Kusakabe, K. Nagao, T. Nakamura, Antarct. Meteorite Res. 11, 122 (1998); see also (11)].
14. There are some similarities in mineralogy among OIs, olivine-pyroxene inclusions (OPIs) [G. J. MacPherson et al., Proc. Lunar Planet. Sci. Conf. 15, J. Geophys. Res. Suppl. 89, C299 (1984)], spinel-pyroxene-olivine inclusions (SPOIs) [R. C. Greenwood et al., Geochim. Cosmochim. Acta 58, 1913 (1994)], and amoeboid olivine aggregates (AOAs) [L. Grossman and I. M. Steel ibid. 40, 149 (1976)]. However, OIs are made predominantly of forsterite, unlike OPIs and SPOIs. OIs resemble Allende AOAs in their high olivine proportions but are much more compact than the latter. OIs and AOAs [A. Hashimoto and L. Grossman, ibid. 51, 1685 (1987)] are clearly distinguished from CAIs in mineral proportions, textures, chemistry, and overall morphologies.
15. There are some similarities in mineralogy among OIs, olivine-pyroxene inclusions (OPIs) [G. J. MacPherson et al., Proc. Lunar Planet. Sci. Conf. 15, J. Geophys. Res. Suppl. 89, C299 (1984)], spinel-pyroxene-olivine inclusions (SPOIs) [R. C. Greenwood et al., Geochim. Cosmochim. Acta 58, 1913 (1994)], and amoeboid olivine aggregates (AOAs) [L. Grossman and I. M. Steel ibid. 40, 149 (1976)]. However, OIs are made predominantly of forsterite, unlike OPIs and SPOIs. OIs resemble Allende AOAs in their high olivine proportions but are much more compact than the latter. OIs and AOAs [A. Hashimoto and L. Grossman, ibid. 51, 1685 (1987)] are clearly distinguished from CAIs in mineral proportions, textures, chemistry, and overall morphologies.
16. There are some similarities in mineralogy among OIs, olivine-pyroxene inclusions (OPIs) [G. J. MacPherson et al., Proc. Lunar Planet. Sci. Conf. 15, J. Geophys. Res. Suppl. 89, C299 (1984)], spinel-pyroxene-olivine inclusions (SPOIs) [R. C. Greenwood et al., Geochim. Cosmochim. Acta 58, 1913 (1994)], and amoeboid olivine aggregates (AOAs) [L. Grossman and I. M. Steel ibid. 40, 149 (1976)]. However, OIs are made predominantly of forsterite, unlike OPIs and SPOIs. OIs resemble Allende AOAs in their high olivine proportions but are much more compact than the latter. OIs and AOAs [A. Hashimoto and L. Grossman, ibid. 51, 1685 (1987)] are clearly distinguished from CAIs in mineral proportions, textures, chemistry, and overall morphologies.
17. There are some similarities in mineralogy among OIs, olivine-pyroxene inclusions (OPIs) [G. J. MacPherson et al., Proc. Lunar Planet. Sci. Conf. 15, J. Geophys. Res. Suppl. 89, C299 (1984)], spinel-pyroxene-olivine inclusions (SPOIs) [R. C. Greenwood et al., Geochim. Cosmochim. Acta 58, 1913 (1994)], and amoeboid olivine aggregates (AOAs) [L. Grossman and I. M. Steel ibid. 40, 149 (1976)]. However, OIs are made predominantly of forsterite, unlike OPIs and SPOIs. OIs resemble Allende AOAs in their high olivine proportions but are much more compact than the latter. OIs and AOAs [A. Hashimoto and L. Grossman, ibid. 51, 1685 (1987)] are clearly distinguished from CAIs in mineral proportions, textures, chemistry, and overall morphologies.
18. There are some similarities in mineralogy among OIs, olivine-pyroxene inclusions (OPIs) [G. J. MacPherson et al., Proc. Lunar Planet. Sci. Conf. 15, J. Geophys. Res. Suppl. 89, C299 (1984)], spinel-pyroxene-olivine inclusions (SPOIs) [R. C. Greenwood et al., Geochim. Cosmochim. Acta 58, 1913 (1994)], and amoeboid olivine aggregates (AOAs) [L. Grossman and I. M. Steel ibid. 40, 149 (1976)]. However, OIs are made predominantly of forsterite, unlike OPIs and SPOIs. OIs resemble Allende AOAs in their high olivine proportions but are much more compact than the latter. OIs and AOAs [A. Hashimoto and L. Grossman, ibid. 51, 1685 (1987)] are clearly distinguished from CAIs in mineral proportions, textures, chemistry, and overall morphologies.
19. Careful SEM-EDS observations suggest that at least 15 and 40 OIs of similar morphologies are present in the thin sections of Y-86009 (5 mm by 5 mm) and Murchison (6 mm by 7.5 mm), respectively, which suggests that OIs are rather abundant in these meteorites. In fact, the four Murchison OIs studied here were randomly chosen from more than 40 OIs that we had recognized before the ion microprobe analyses, and all of them were found to have large oxygen isotopic anomalies.
20. Pyroxene is fassaitic to diopsidic in composition with variable aluminum content. Feldspathic phase is a fine-grained mixture of anorthitic plagioclase and grossular, which is probably an alteration product of melilite.
21. Olivine in these chondrules is very Mg-rich [Mg number (Mg#) = 99.3 for both of two], which is comparable to those in OIs, but its oxygen isotopic composition (measured only for Y86009-F) is much less anomalous than the latter, indicating that Mg# alone cannot be a measure of the degree of oxygen isotopic anomalies.
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24. 16O on average [K. Liffman and D. D. Clayton, Proc. Lunar Planet. Sci. Conf. 18, 657 (1988); D. D. Clayton, Astrophys. J. 334, 191 (1988); _, P. Scowmen, K. Liffman, ibid. 346, 531 (1989)]. However, this model may also have difficulties in explaining the uniqueness of the oxygen isotopic anomalies observed in various objects, especially similar anomalies both inside and on the rims of CAIs (9).
25. 16O on average [K. Liffman and D. D. Clayton, Proc. Lunar Planet. Sci. Conf. 18, 657 (1988); D. D. Clayton, Astrophys. J. 334, 191 (1988); _, P. Scowmen, K. Liffman, ibid. 346, 531 (1989)]. However, this model may also have difficulties in explaining the uniqueness of the oxygen isotopic anomalies observed in various objects, especially similar anomalies both inside and on the rims of CAIs (9).
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30. Wark-Lovering rims are sequences of mineralogically distinct layers enclosing CAIs with total thickness of ∼50 μm [D. A. Wark and J. F. Lovering, Proc. Lunar Planet. Sci. Conf. 8, 95 (1977); G. J. MacPherson, L. Grossman, J. M. Allen, J. R. Beckett, ibid. 12, 1079 (1981)].
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32. Accretionary rims are layers of fine-grained materials mantling CAIs that are most notable at their topographic depression [G. J. MacPherson, A. Hashimoto, L. Grossman, Geochim. Cosmochim. Acta 49, 2267 (1985)].
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36. The Yamato-86009 CV3 chondrite sample was supplied by the National Institute of Polar Research, Japan. This work was financially supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, Japan (no. 09440183 to H.H.).