Computer Science
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29s.487k&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 487-488
Computer Science
3
Antarctic Regions, Chemical Composition, Meteoritic Composition, Micrometeoroids, Oxygen Isotopes, Spinel, Inclusions, Secondary Ion Mass Spectrometry, Silicates, Trace Elements
Scientific paper
Spinel-rich inclusions were found in a large unmelted micrometeorite (MM) from Antarctica. This particle (MM92/15-23) consists of a fine-grained matrix of dehydrated former phyllosilicates that enclose a few small olivines, one large chromite, and several spinel-rich inclusions. The latter form elongated to rounded bodies up to 35 microns in length and consist of a spinel core enveloped by a Fe-rich silicate phase that probably is a (dehydrated?) phyllosilicate -- too small to be analyzed with the electron microprobe. A few very small perovskite grains are enclosed within the spinel. The chemical composition of the spinel is that of a Mg-Al spinel. On top of the Fe-rich silicate envelopes there is a discontinuous rim of aluminous Ca-rich pyroxene with a fairly high FeO content. The trace-element content is determined by secondary ion mass spectrometry (SIMS) of these inclusions resembles that of group II CAIs. Meanwhile we have found a second Antartic micrometeorite containing a few spinel grains. This spinel is associated with some tiny ilmenite grains and embedded in the foamy melt matrix of scoriaceous micrometeorite particle MM94/1-28. The chemical composition of the spinel is that of a Mg-Al-spinel containing small amounts of FeO (0.6 wt%), but no Cr2O3. We have successfully analyzed the O isotopic composition of two spinels from MM92/15-23 and one from MM94/1-28. The most common matter accreting onto the Earth today and represented by unmelted and partially melted micrometeorites consists of a matter similar, but not identical, to CM carbonaceous chondrites. The presence of spinel-rich Ca-Al rich inclusions (CAIs) with trace-element contents and O isotopic compositions of group II inclusions provides an additional support of that view.
Engrand Cécile
Hoppe Peter
Kurat Gero
Maurette Michel
Walter Jürgen
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