Mathematics – Logic
Scientific paper
Sep 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..621g&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 5, p. 621-631
Mathematics
Logic
9
Canada, Geochemistry, Impact Melts, Lithology, Meteorite Craters, Meteorites, Petrography, Rocks, Chromium, Cobalt, Lakes, Nickel, Pyroxenes, Samples, Sediments
Scientific paper
The approx. 7.5 diameter Wanapitei impact structure (46 deg 45 min N; 80 deg 45 min W) lies entirely within Lake Wanapitei in central Ontario, Canada. Impact lithologies are known only from glacial float at the southern end of the lake. Over 50% of the impact lithologies recovered from this float can be classified as suevite, less than 20% as highly shocked and partially melted arkosic metasediments of the target rock Mississagi Formation or, possibly, the Serpent Formation and less than 20% as glassy impact melt rocks. An additional less than 5% of the samples have similarities to the suevite but have up to 50% glass clasts and are tentatively interpreted as fall-back material. The glassy impact melt rocks fall into two textural and mineralogical types: a perlitically fractured, colorless glass matrix variant, with microlites of hypersthene with up to 11.5% Al2O3 and a 'felted' matrix variant, with evidence of flow prior to the crystallization of tabular orthopyroxene. These melt glasses show chemical inhomogeneities on a microscopic scale, with areas of essentially SiO2, even when appearing optically homogeneous. They are similar in bulk composition for major elements, but the felted matrix variant is approx. 5x more enriched in Ni, Co and Cr, the interelement ratios of which are indicative of an admixture of a chondritic projectile. Mixing models suggest that the glassy impact melt rocks can be made from the target rocks in the proportions: approx. 55% Gowganda wacke, approx. 42% Serpent arkose and approx. 3% Nipissing intrusives. Geologic reconstructions suggest that this is a reasonable mixture of potential target rocks at the time of impact.
Ber T. J.
Grieve Richard A. F.
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