Impact diamonds in the Suevitic Breccias of the Black Member of the Onaping Formation, Sudbury Structure, Ontario, Canada

Abstract

Eleven samples (mostly of the Onaping Formation) from the 1.85-Ga Sudbury impact structure were examined with respect to their carbon phases. Six impact diamonds, <0.6 mm in diameter, were discovered in two samples of the Black Member of the Onaping Formation. These diamonds occur in a variety of colors, are cubic, and are generally friable due to inclusions and polycrystallinity. In one case, the hexagonal phase lonsdaleite was detected. According to transmission electron microscopy analyses, the mean grain size of individual diamond crystallites is in the range 50-100 nm. The diamonds are pervaded by numerous planar defects parallel to {111} and are organized in 100-200-nm-thick-bands, presumably inherited from precursor graphite. The diamonds were produced by the solid state transformation of graphite. Impact diamonds from the Onaping Formation are similar to other impact diamonds and are yet another expression of the effects of shock metamorphism at the Sudbury impact structure.

The search for fullerenes in rocks from the Ries impact crater

“…The source of carbon for the fullerenes at Sudbury has not been successfully explained yet, though it seems that the target rocks contained little carbon (Heymann et al 1999). This suggestion was made upon a remarkable observation that "shock metamorphosed carbons," such as chaoite and diamond, are very rare at Sudbury (Masaitis et al 1997). Also the distribution of fullerenes in Sudbury is very heterogeneous (Heymann et al 1999).…”

“…The gray, green, and black members contain recrystallized glass fragments (Dressler et al 1996). Masaitis et al (1997) observed shockproduced diamonds in the breccias of the black member.…”

Economic Deposits at Terrestrial Impact Structures

“…Siebenschock et al, 1998) failed to find either cubic diamond or SiC at the Ries. Silicon carbide has also been reported from the Onaping Formation at the Sudbury impact structure (Masaitis et al, 1999). It is associated with impact diamonds that are a mixture of cubic diamond and hexagonal lonsdaleite from the solid-state transformation of precursor graphite in carbonaceous Huronian target lithologies by shock compression.…”

Economic natural resource deposits at terrestrial impact structures

“…Siebenschock et al 1998) failed to find either cubic diamond or SiC at the Ries. Silicon carbide, however, has been reported from the Onaping Formation at the Sudbury impact structure (Masaitis et aL 1999). In this location, it is associated with impact diamonds that are a mixture of cubic diamond and hexagonal lonsdaleite, resulting not from chemical vapour deposition but from solid-state transformation by shock of precursor graphite.…”