Petrography, geochemistry, and Hf‐Nd isotope evolution of drill core samples and target rocks from the El'gygytgyn impact crater, NE Chukotka, Arctic Russia

Abstract

AbstractEl'gygytgyn in northeast Chukotka (Russia) is a 3.6 Ma, 18‐km‐diameter impact structure. The impact crater was recently drilled in the framework of a project sponsored by the International Continental Scientific Drilling Program (ICDP). Target rocks at the El'gygytgyn area are dominated by the felsic members of the Late Cretaceous Okhotsk‐Chukotka Volcanic Belt (OCVB). Such a target lithology is unique among terrestrial impact craters, thereby providing the opportunity to study shock metamorphism in siliceous volcanic rocks. Here, we present a petrographic, geochemical, and isotopic study of the section of the drill core underneath the lacustrine sediments, extending from ∼316 m to 517 m below the lake bottom (blb). The drill core stratigraphy includes ∼80 m of suevite and a cross section through a volcanic suite, which consists of (1) a middle section (∼390–423 mblb) with dominant felsic tuffs and a few mafic members, and (2) a welded rhyolitic‐dacitic ignimbrite (∼423–517 mblb). The melt fragments embedded in the suevite are interpreted as being impact‐related by comparison with impact glasses from the crater and in opposition to the target rock, which does not include similar melts. A suevitic dyke crosscuts the lower section of the core at the depth 471.40 mblb. Evidence for shock metamorphism is concentrated in the upper 10 m of the drill core and almost limited to the suevitic breccia. The geochemical and isotope (Nd and Hf) composition of samples from the target and the drill core reveals relationships to the “Berlozhya magmatic assemblage” (BMA) arguing for similar source magmas. The primitive upper mantle (PUM)‐normalized trace element plot of rocks investigated here confirms a subduction‐related signature, as previously proposed for rocks from both OCVB and BMA.