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

Abstract

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 and bodies of suevites and tagamites. The results of studying the U‒Th‒Pb isotope 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 dates of detrital zircons from all studied samples is 258 ± 7 Ma, which corresponds to the Late Permian. We take this date as the lower age limit of the Puchezh breccias. The age sets of detrital zircon grains from the studied samples and from (1) crystalline rocks of the Vorotilov knoll and suevites of the ring depression and (2) Upper Permian–Lower Triassic sandstones of the Zhukov Ravine reference section (Moscow Syneclise) were compared. The absence of zircon grains, whose U‒Th‒Pb isotope system is similar to the parameters of those from the rocks of the Vorotilov knoll and suevites among the detrital zircons from the Puchezh breccia indicates the local nature of the Puchezh–Katunki explosion, the impact-thermal impact of which did not affect the detrital zircons in rocks of the marginal part of the ring terrace of the crater. A high degree of similarity of the age sets 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 reworking of the Upper Permian–Lower Triassic sequences underlying the explosive formations. We consider the Uralian paleo-orogenic belt as the main provenance area 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.