Notes on some impact rocks from the Janisjarvi structure, Karelia, Russia
The Janisjarvi impact structure is located on the northern edge of Ladoga Lake, in Karelia, Russia. This research was carried out to study the biotite-quartz-feldspar-garnet-staurolite schist and several impact-metamorphosed rocks. In schist, biotite inclusions in garnet, pleochroic fields in biotit...
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| Format: | Article in Journal/Newspaper |
| Language: | English |
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Polskie Towarzystwo Meteorytowe
2021
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| Online Access: | https://bibliotekanauki.pl/articles/1830273.pdf https://bibliotekanauki.pl/articles/1830273 |
| Summary: | The Janisjarvi impact structure is located on the northern edge of Ladoga Lake, in Karelia, Russia. This research was carried out to study the biotite-quartz-feldspar-garnet-staurolite schist and several impact-metamorphosed rocks. In schist, biotite inclusions in garnet, pleochroic fields in biotite and asymmetry in the staurolite-biotite contact were observed. These characteristics were related to regional metamorphism of the target rock, and impact-induced features were not detected. No ‘kinky’ bands were observed in biotite. Fluidal structures and undulose extinction were rare in the analysed specimens. Injections of the tagamite melt into the clasts of cataclased recrystallising glass were noted. Fine-grained grey impact rock was cemented by a glassy micro-net with specimens of recrystallising quartz paramorphosis. In most of the analysed impactites, isotropic spherules and ‘ballen quartz’ structures, as well as sets of PDF (planar deformation features) and PF (planar fractures) in tagamite and quartz paramorphosis specimens were recognised. Except in schist, dynamic recrystallisation by ‘boundary migration’ was common. Secondary mineralisations were found for iron oxides, chlorite and calcite. Struktura uderzeniowa Janisjarvi znajduje się na północnym skraju jeziora Ładoga w rosyjskiej Karelii. Analizowano łupek typu biotyt-kwarc-skaleń-granat-staurolit ze skał podłoża struktury oraz kilka skał poddanych metamorfozie uderzeniowej. W łupku odkryto inkluzje biotytowe w granacie, pola pleochroiczne w biotycie i asymetrię kontaktu staurolit-biotyt. W biotycie nie zaobserwowano pasm typu ‘kinky’. Struktury fluidalne i faliste wygaszanie światła były rzadkie w analizowanych okazach. Odnotowano injekcje stopu tagamitu w klasty skataklazowanego rekrystalizującego szkliwa. Okaz rekrystalizującej paramorfozy kwarcu był scementowany z drobnoziarnistą skałą impaktową mikrosiecią szkliwa. W większości analizowanych impaktytów rozpoznano izotropowe sferule i struktury ’kwarcu groniastego’, a w tagamicie i ... |
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