EL'GYGYTGYN, AN IMPACT CRATER IN SILICEOUS VOLCANIC ROCKS: PRELIMINARY RESULTS FROM THE IGCP DRILLING PROJECT

In 2009, the El’gygytgn impact crater in northeastern Siberia, Arctic Russia, was drilled within the framework of an ICDP (International Continental Scientific Drilling Program) project. The 18-km-diameter impact structure is 3.6 Myr old. El’gygytgyn is the only known impact structure on Earth, which was excavated in siliceous volcanic rocks (mostly ignimbrite, tuff, and rhyolite lava). The study of the drilled core allows us to investigate shock metamorphism in such rocks, as an analogue of impact craters in related terrains on other terrestrial planets.

The studied core begins at 318.83 m below the lake floor, underlying the post-impact sedimentary sequence, and ends at 517.30 m. The whole core can be subdivided into three main units: (i) sedimentary breccia with grey/reddish sandy/clay matrix and large clasts of volcanic rocks (mostly white pumice and dark rhyolite); (ii) highly fractured transition zone with breccia intercalated to suevite, extended from ~392 to ~404 m depth; (iii) greenish suevite. The green color of the suevite is due to alteration and the abundance of sheet minerals in the matrix; it contains abundant black melt clasts. The suevite shows a strong anisotropic fabric, with fluidal texture. Fractures crosscutting the suevite are common, as are green clay and/or white-reddish carbonate veins.

Along the core more than 200 samples have been selected for a detailed study of shock effects and their spatial variation with depth. The distinction between volcanic and impact-derived features is a main topic as well. At the meeting we will present results of the first geochemical and petrographic investigations.