The Boltysh impact structure and its impact melt rocks
© Gurov E.P., Shehunova S.B., Permyakov V.V.
The Boltysh crater in the central part of the Ukrainian Shield is a complex impact structure composed by a deep inner crater with a central uplift and a peripheral depression. The powerful annular sheet of impact melt rocks fills the inner crater around the central uplift. Two main types of impact melt rocks are presented in the sheet: the microporphyric rocks with glassy matrix and rocks with crystalline matrix without any glass. While the glassy matrix melt rocks are the product of solidification of a dry melt, the crystalline matrix melt rocks were formed in the marginal zones of the sheet by interaction with water and water-bearing substances. The age of the Boltysh structure is 65,17±0,64 Ma that is an evidence of its formation at the Cretaceous-Tertiary boundary simultaneously with the Chixhulub crater in Mexico, which caused a mass life extinction at the end of the Mesozoic.