Argon‐40/argon‐39 age of the El'gygytgyn impact event, Chukotka, Russia

Abstract

Abstract— Lake El'gygytgyn, Chukotka, Russia, lies in a ∼18 km crater of presumably impact origin. The crater is sited in Cretaceous volcanic rocks of the Okhotsk‐Chukotka volcanic belt. Laser 40 Ar/ 39 Ar dating of impact‐melted volcanic rocks from the rim of Lake El'gygytgyn yields a 10‐sample weighted plateau age of 3.58 ± 0.04 Ma. The Ar step‐heating method was critical in this study in identifying inherited Ar in the samples due to incomplete degassing of the Cretaceous volcanic rocks during impact melting. This age is consistent with, but more precise than, previous K‐Ar and fission‐track ages and indicates an “instantaneous” formation of the crater. This tight age control, in conjunction with the presence of impactites, shocked quartz, and other features, is consistent with an impact origin for the structure and seems to discount internal (volcanogenic) origin models.