New data on spherules from the region of the El’gygytgyn crater

Abstract-El'gygytgyn is a 3.6 Ma, 18 km diameter, impact crater formed in an approximately 88 Ma old volcanic target in Northeast Siberia. The structure has been the subject of a recent ICDP drilling project. In parallel to those efforts, a Russian-German expedition was undertaken in summer 2011 to investigate the permafrost soil, lake terraces, and the volcanic rocks of the southern and eastern crater rim. This provided the unique opportunity for mapping and sampling of the volcanic target rocks around a large part of this complex impact structure. Samples from 43 outcrops were collected and analyzed petrographically and geochemically. The results were combined with earlier mapping outcomes to create a new geological map of this impact structure and its immediate environs, at the scale of 1:50,000. Compositions of our rock suites are compared with the lithologies of the 2009 ICDP drill core. The ignimbrite described as lower bedrock in the ICDP drill core shows petrographically and chemically strong similarities to the rhyolitic and rhyodacitic ignimbrites observed on surface. The suevite sequence exposed in the ICDP drill core is a mixture of all observed target rocks at their respective proportions in the area. In contrast to previous studies, the calculated average target composition of El'gygytgyn takes the contribution of the basic target rocks into consideration: mafic and intermediate rocks approximately 7.5%, and felsic rocks approximately 92.5%.

Section: Introductionmentioning

confidence: 69%

“…Such spherules were also analyzed by Adolph and Deutsch (), Smirnov et al. (), and Wittmann et al. (), who concluded that they represent impact‐produced melt droplets that had been deposited from the collapsing ejecta plume into a thin layer on the juvenile surface of the impact structure.…”

Section: Introductionmentioning

confidence: 97%

The 2011 expedition to the El'gygytgyn impact structure, Northeast Russia: Toward a new geological map for the crater area

Raschke

Zaag

Schmitt

et al. 2014

“…2. Up to 1.5 mm size glass spherules found in lacustrine sediments to the south of the crater (during the Quaternary, lake El'gygytgyn covered a larger surface area and had a higher lake level) and in fluvial terraces along the Enmyvaam River (Gurov et al 1979;Glushkkova and Smirnov 2007) were analyzed by Adolph and Deutsch (2010), Smirnov et al (2011), and Wittmann et al (2013). All these authors concluded, on the basis of geochemical data, that the spherules were impact-produced melt droplets that had been deposited from the collapsing ejecta plume (with lithic debris) in a thin layer on the juvenile postimpact surface.…”

Section: Impact and Volcanic Melt Rocks In The Crater Area And In Thementioning

confidence: 99%

“…; Glushkkova and Smirnov ) were analyzed by Adolph and Deutsch (), Smirnov et al. (), and Wittmann et al. ().…”

Section: Introduction and Geological Backgroundmentioning

confidence: 99%

Geochemical studies of impact breccias and country rocks from the El'gygytgyn impact structure, Russia

Raschke

Schmitt

McDonald

et al. 2015

“…The ejecta blanket, composed of unshocked and shocked rocks, as well as fragments of the impact breccia, is almost completely eroded as a result of Arctic weathering. However, impact melt rocks (mainly glasses) are found on lacustrine terraces inside the crater and, to a minor extent, embedded in fluvial terraces outside the crater rim (e.g., Smirnov et al 2011;Raschke et al 2014). Occurrences of larger centimeter-sized cobbles and meter-sized blocks are restricted to recent terraces (Gurov and Koeberl 2004;Raschke et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Strontium and neodymium isotope systematics of target rocks and impactites from the El'gygytgyn impact structure: Linking impactites and target rocks

Wegner

Koeberl

2016

The 3.6 Ma El'gygytgyn structure, located in northeastern Russia on the Chukotka Peninsula, is an 18 km diameter complex impact structure. The bedrock is formed by mostly high‐silica volcanic rocks of the ~87 Ma old Okhotsk‐Chukotka Volcanic Belt (OCVB). Volcanic target rocks and impact glasses collected on the surface, as well as drill core samples of bedrock and impact breccias have been investigated by thermal ionization mass spectrometry (TIMS) to obtain new insights into the relationships between these lithologies in terms of Nd and Sr isotope systematics. Major and trace element data for impact glasses are added to compare with the composition of target rocks and drill core samples. Sr isotope data are useful tracers of alteration processes and Nd isotopes reveal characteristics of the magmatic sources of the target rocks, impact breccias, and impact glasses. There are three types of target rocks mapped on the surface: mafic volcanics, dacitic tuff and lava of the Koekvun’ Formation, and dacitic to rhyolitic ignimbrite of the Pykarvaam Formation. The latter represents the main contributor to the impact rocks. The drill core is divided into a suevite and a bedrock section by the Sr isotope data, for which different postimpact alteration regimes have been detected. Impact glasses from the present‐day surface did not suffer postimpact hydrothermal alteration and their data indicate a coherent alteration trend in terms of Sr isotopes with the target rocks from the surface. Surprisingly, the target rocks do not show isotopic coherence with the Central Chukotka segment of the OCVB or with the Berlozhya magmatic assemblage (BMA), a late Jurassic felsic volcanic suite that crops out in the eastern part of the central Chukotka segment of the OCVB. However, concordance for these rocks exists with the Okhotsk segment of the OCVB. This finding argues for variable source magmas having contributed to the build‐up of the OCVB.