Mathematics – Logic
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.515g&link_type=abstract
Meteoritics, vol. 30, no. 5, page 515
Mathematics
Logic
4
Diamonds, Earth, Impact Craters, Shock Metamorphism
Scientific paper
The impact diamonds discovery and investigations in the rocks of the Popigay crater [1,2] stimulated the search of the carbon high pressure phases in the craters of the Ukrainian shield. Seven impact craters are located on the territory of the Ukrainian Shield and its North-Eastern slope. Impact diamonds were discovered in the rocks of the Ilyinets, Zapadnaya, Obolon craters and some other impact structures. The highest concentration of impact diamonds was determined in the Zapadnaya crater. The Zapadnaya impact crater, about 3 km in diameter, is located in the Western part of the Ukrainian shield. The target of the crater is presented by granites and gneisses of the Precambrian crystalline basement. The Zapadnaya crater is represented the intensively eroded astrobleme of a complex structure. The inner crater with the conelike central uplift preserves only at the recent erosional level [3,4]. The allochthonous rocks complex in the crater is presented by the suevites, breccia and impactites. The allochthonous breccia forms the lowermost layer in the crater. The suevites with the glass content from 10-15 to 40-50% compose the upper annular layer around the central uplift. The massive impactites form the dykelike veins in the brecciated rocks of the subcrater basement. The impact diamonds occur in suevites and massive impactites of the crater. The diamonds are represented with the tabular grains from tens of micron up to 0.4-0.5 mm in diameter. The colour of the diamond grains changes from colourless, white and yellowish to grey, dark grey and black. The diamonds are anisotropic, their birefringence is up to 0.015. The impact diamonds phase composition was investigated with X-ray methods. The diamond grains are represented by the submicroscopic aggregates of cubic and hexagonal phases. The cubic phase prevalents in all investigated diamonds; the hexagonal phase content in the diamonds from the Zapadnaya crater changes from 5-10 to 40-50%. The direct dependence of the birefringence from the hexagonal phase content in the diamond grains was estimated. The impact diamonds of the rocks of the Ilyinets and Obolon craters have the same characteristics that the diamonds of the Zapadnaya crater. References: [1] Masaitis V. L. et al. (1972) Zapiski Vsesoyuznogo Mineralogicheskogo Obshchestva, 101, 108-112, in Russian. [2] Vishnevsky S. A. and Palchik N. A. (1975) Geol. Geophys., 1, 67-75, in Russian. [3] Gurov E. P. et al. (1985) Doklady AN UKRSSR, 1, 9-12, in Russian. [4] Gurov E. P. and Gurova H. P. (1991) Geological Structure and Composition of Rocks in Impact Craters, Naukova, Kiev, 160 pp., in Russian.
Gurov Eugene P.
Gurova E. P.
Rakitskaya R. B.
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