Are the most C-rich antarctic micrometeorites exotic?

Details Are the most C-rich antarctic micrometeorites exotic? Are the most C-rich antarctic micrometeorites exotic?

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.464e&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 464

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Antarctic Regions, Carbon, Chemical Composition, Meteoritic Composition, Micrometeoroids, Mineralogy, Electron Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscopy

Scientific paper

A 400-kV transmission electron microscope, equipped with both energy dispersive spectroscopy (EDS) and EELS (electron energy loss spectrometer) systems, has been first used to determine the C/O ratio and the concentrations of major elements on approximately equal 1000-A-zones of micrometer-sized crushed fragments from about 30 Antarctic micrometeorites, with initial sizes ranging from approximately equal 30 microns up to 300 microns. Another fragment of each micrometeorite was polished and the mineralogy of its assemblage of greater than 5-microns grains was determined with an scanning electron microscope (SEM) equipped with an EDS system, and with an electron microprobe. Another fragment of a few C-rich and C-poor micrometeorites were ultramicrotomed for further TEM observations. Finally, textural changes upon in-situ pyrolysis (from 400 up to 1000 C) in a 3-MV microscope were continuously monitored with a video camera in preselected C-rich crushed grains already analyzed at ONERA; modifications of their C/O ratios and chemical compositions were subsequently investigated at ONERA. The major result of this investigation are C-rich grains within a single micrometeorite. All the grains are amorphous, and they frequently show high contents of Ni, indicative of their 'extraterrestrial' origin. With exception of the crystalline and scoriaceous particles, the C-poor-fine-grained micrometeorites contain already as much C as Murchison. But approximately 20% of them have much higher contents of C than Orgueil. These C-rich micrometeorites are in fact very similar to the other micrometeorites, with some of the scoriaceous particles containing more carbonaceous material than a truly unmelted fine-grained micrometeorite. The fine-grained micrometeorites also show similar differences between their assemblage of 'large' and small minerals, with the largest minerals being related to CM and CR meteorites, and the finest-sized grains bearing similarities to CV and CO meteorites.

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