Source: GeoIJNES 16 (2003)

Search for Fullerenes in Rocks from Ries Impact Crater

Ota FRANK1, Jan JEHLIČKA1 and Věra HAMPLOVБ2
1  Institute of Geochemistry, Faculty of Science, Charles University in Prague, Albertov 6, 128 43 Praha 2, Czech Republic
2  Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Praha 8, Czech Republic

Fullerenes have been so far identifed in a few rock types with unique geological history. One group of these fnds is related to impacts of extraterrestrial bodies on Earth surface, strictly speaking the impact structure of Sudbury (Becker et al., 1994) and to events recorded from Permian/Triassic (Becker et al., 2001) and Cretaceous/Tertiary boundaries (Heymann et al., 1994). Generally two basic hypotheses have been proposed for the origin of fullerenes at these sites. The frst one considers formation of fullerenes during the impact, the latter supposes their extraterrestrial origin. To elucidate this problem, we searched for fullerenesin the Ries impact structure, Germany, where the target rocks are carbon-rich and thus could have been the source of carbon in the fullerenes, if they are to be formed during the impact.

The Ries impact crater lies in southeastern Germany. It is approximately a circular structure with the inner diameter of 25 km, 15 Ma in age. Impact breccias from the Ries crater, the suevites, can be differentiated to various classes depending on the grade of shock metamorphism, where the highest ranked classes comprise mainly glass. Considering our previous works on fullerenes in rocks, one of the most important
factors of fullerene survival till the present is the matrix of rock in which fullerenes could be preserved from weathering, especially from the infuence of molecular oxygen and ozone and ultraviolet radiation. Suevites of lower metamorphic class are affected predominantly mechanically, with weak thermal transformation, and show low stability against weathering. On the contrary, impact glasses from the Ries crater are far less weathered, thus they represent almost ideal medium for fuller-ene conservation. In addition, moldavite tektites, which can be interpreted as condensates of vaporized, surfcial sediments (Vonengelhardt et al., 1995), have been chosen as another possible carrier of fullerenes that could originate during the Ries impact event. And as for suevite glasses, moldavites are very stable under air conditions.

In the frst step, suevites containing larger amounts of glass from Otting (Ries crater, Germany) were sampled and – together with moldavite samples from Habřн (Czech Republic) – subjected to demineralization in a mixture of HF and HCl acids (2:1), the residuum in HF only, then repeatedly washed in distilled water. This was followed by a 2-hour ultrasound toluene extraction of the remaining material and HPLC analysis us ing Buckyprep analytical column 4.6mmI.D.x250mm (method tested and conf rmed by Jehlička et al., 2000).

Retention spectra of toluene extracts of the natural samples were compared to spectra of C60 standard (Fig. 1a) with a clear peak at 7.980 minutes. No such fullerene C60 peak has been observed in moldavite samples in concentration higher than 0.01 ppm. Signs of peaks with retention times 7.910 and 13.562 (approximately C70) can be observed in retention spectrum of the Otting suevite (Fig. 1b), nevertheless, with such a weak signal it is impossible to conf rm the presence of fullerenes from these results.

Fullerene C60 has not been identif ed in the toluene extract of moldavite from Habřн, Czech Republic. The presence of fullerenes C60 and C70 in the extract of suevite from Otting locality in the Ries impact crater, Germany, could not be con-f rmed or disproved. Further analyses of suevites sampled in the Ries crater will be carried out with higher amounts of material used for demineralization and extraction. The absence of fuller-enes in toluene extracts of moldavites ref ects small amount of insoluble residuum after demineralization.

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