The Nature of the Puchezh-Katunki Impact Structure (the Central Part of the East European Platform): Results of the U‒Th‒Pb Isotope System Study of Detrital Zircons from Explosive Breccias

The Puchezh-Katunki crater is located in the central part of the East European Platform in the area of the Gorky Reservoir, has a diameter of ~80 km and is morphologically expressed by the central uplift of the basement (Vorotilov knoll) and the ring depression surrounding it, on the periphery of which there is a ring terrace. The crater is filled with various coptogenic (explosive (?)) formations – breccias of various types, bodies of suvites and tagamites. The results of studying the U‒Th‒Pb isotopic system of detrital zircon grains from variegated explosive Puchezh breccias in the northwestern part of the ring terrace (three samples) are presented. The weighted average of the three youngest U‒Pb datings of detrital zircon from all studied samples is 258 ± 7 Ma, which corresponds to the Late Permian. We took this dating as the lower age limit of the Puchezh breccias. A comparison of the age sets of detrital zircon grains from the samples studied by us and from (i) crystalline rocks of the Vorotilov knoll and ring depression suvites and (ii) Upper Permian–Lower Triassic sandstones of the Zhukov ravine reference section (Moscow syneclise) was carried out. The absence among the detrital zircon from the Puchezh breccia grains, whose U‒Th‒Pb isotopic system is comparable with the parameters of zircon from the rocks of the Vorotilov knoll and suvites, indicates the local nature of the Puchezh-Katunki explosion, in which the impact-thermal impact did not affect the detrital zircons in rocks of the marginal part of the annular terrace of the crater. The high similarity of the sets of ages of detrital zircon grains from the lens of redeposited sandstones of the Puchezh breccias and Upper Permian rocks of the Zhukov ravine section indicates that the Puchezh breccias were formed mainly due to the recycling of the Upper Permian–Lower Triassic sequences underlying the explosive formations. We consider the Uralides paleoorogen as the main source for the deposits of the central regions of the East European Platform in the stratigraphic interval close to the Permian–Triassic boundary. The deposits were formed as a result of a high degree of mixing and averaging of clastic material of sedimentary flows containing the Uralian and Asha provenance signals.