SHOCKED LITHOLOGIES AT THE WANAPITEI IMPACT STRUCTURE, ONTARIO, CANADA

The approximately 7.5 km diameter Wanapitei impact structure (46-degre es-45'N; 80-degrees-45'W) lies entirely within Lake Wanapitei in centr al Ontario, Canada. Impact lithologies are known only from glacial flo at at the southern end of the lake. Over 50% of the impact lithologies recovered from this float can be classified as suevite, <20% as highl y shocked and partially melted arkosic metasediments of the target roc k Mississagi Formation or, possibly, the Serpent Formation and <20% as glassy impact melt rocks. An additional <5% of the samples have simil arities to the suevite but have up to 50% glass clasts and are tentati vely interpreted as fall-back material. The glassy impact melt rocks f all into two textural and mineralogical types: a perlitically fracture d, colorless glass matrix variant, with microlites of hypersthene with up to 11.5% Al2O3 and a ''felted'' matrix variant, with evidence of f low prior to the crystallization of tabular orthopyroxene. These melt glasses show chemical inhomogeneities on a microscopic scale, with are as of essentially SiO2, even when appearing optically homogeneous. The y are similar in bulk composition for major elements, but the felted m atrix variant is approximately 5x more enriched in Ni, Co and Cr, the interelement ratios of which are indicative of an admixture of a chond ritic projectile. Mixing models suggest that the glassy impact melt ro cks can be made from the target rocks in the proportions: approximatel y 55% Gowganda wacke, approximately 42% Serpent arkose and approximate ly 3% Nipissing intrusives. Geologic reconstructions suggest that this is a reasonable mixture of potential target rocks at the time of impa ct.