Computer Science
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27..309y&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 309
Computer Science
2
Scientific paper
An acid-resistant residue prepared from Greenland cryoconite has been analysed for carbon content and stable isotopic composition in an attempt to determine whether the micrometeorite component contains presolar material (i.e., diamonds and silicon carbide (SiC)) analogous to that found in primitive chondritic meteorites. The cryoconite sample, which was collected ca. 25 km inland of the ice margin at the latitude of Sondre Stromfjord on the west coast of Greenland. was treated with HF/HCl, Cr(sub)2O(sub)7^2- and HClO4 according to normal procedures. The results of the analysis are presented within the figure; the shaded histogram and the left-hand ordinate axis correspond to the carbon yield for each temperature step (as denoted by the abscissa axis), and the delta^13C value of this carbon is illustrated by the open circles and the right hand ordinate. The carbon release profile is dominated by a low-temperature component with a delta^13C of ca. -30o/oo (as indicated by the 0-400 degrees C steps), which is interpreted as terrestrial organic contamination introduced to the sample after the acid treatments. The isotopic departure at 400-500 degrees C to -34.4 +- 0.4oo/o can be interpreted to represent the combustion of meteoritic presolar diamond, which Russell et al. (1991a) deterrnined to have a delta^13C of -38o/oo in the CM2 meteorites. After making some reasonable assumptions, the abundance of this diamond appears to be in excess of the maximum values suggested by Huss (1990) for the primitive meteorites. It is therefore not inconceivable that some micrometeorites might be more primitive than their larger counterparts, i.e., they could be almost pure fine-grained matrix. The elevation in delta^13C at 1000 degrees C to -7.2 +- 1.1o/oo can be interpreted as the combustion of a small amount of SiC. Prombo et al., (1991) have isolated individual SiC grains from cryoconite for ion probe terrestrial. Analyses of bulk milligram-sized aliquots of SiC used in the preparation of our residues, i.e., a likely contaminant yield average delta^13C of ca.-30oo/o (S.S. Russell, pers.comm.). Correspondingly, the delta^13C obtained here of -7o/oo might indicate the presence of a component of higher delta^13C. Using the average delta^13C for presolar meteoritic SiC of ca. +1400o/oo (Russell et al., l991b), and an estimate of the concentration of micrometeorites within the cryoconite, the abundance of presolar SiC within the micrometeorites can be estimated to a maximum of 40 ppm; this is compatible with the value of 14 ppm derived by Huss (1990) for the most primitive meteorites. The tentative results reported here indicate that further investigation is warranted and additional residues prepared from larger cryoconite samples are to be investigated. References: Huss G.R. (1990) Nature, 347, 159-162. Prombo C.A., Nichols R.H., Alexander C.M.O.D., Swan P.D., Walker R.M. and Maurette M. (1991) Lunar. Planet. Sci. XXII, 1103-1104. Russell S.S., Arden J.W. and Pillinger C.T. (1991a) Science, 254. 1188-1191. Russell S.S., Ash R.D, Pillinger C.T. and Arden J.W. (1991b) Meteoritics, 26, 390.
Arden John W.
Hutchison Robert
Pillinger Colin T.
Wright Ian P.
Yates P. D.
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