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