STRATIGRAPHY AND PETROGRAPHIC-GEOCHEMICAL RESULTS FOR THE IMPACTITE SECTION OF ICDP DRILL CORE D1, EL'GYGYTGYN IMPACT STRUCTURE (RUSSIA)
By now we have studied 110 polished thin sections of core samples and a further 30 from surficial country rocks mainly from the southern part of the crater rim. The core is strongly altered. The polymict impact breccia (315-422 m) contains impact melt particles, diaplectic glass and shocked minerals, and displays some shatter cones. Shock pressures of clasts range from < 10 to 50 GPa and the breccia must be classified as suevite. Clasts and matrix grains cover a size range from mud to stones (20 µm to 20 cm). The parent lithologies identified are a range of volcanic rocks, some of which resemble the lithology of the bedrock sequence. We also identified particles of clayey and fine-grained sediment in the transition zone between suevite and lake sediments. XRF analyses have been conducted on 115 impactite and bedrock core samples. Suevite and brecciated bedrock, as well as the surface samples, cover a similar range of rhyodacitic to basaltic compositions.
The lower unit is brecciated and weakly shocked (< 15 GPa). Phenocrysts are plagioclase, alkali feldspar, quartz, biotite and amphibole, and the groundmass is composed of the same minerals. Melt particles (up to 1 cm in width and 2 to 6 cm long) contain fine-grained phenocrysts embedded in a brownish glassy though altered matrix. Fractures are filled with zeolites. During this summer a field campaign is planned to map the N/E crater rim sectors and to investigate the ejecta layer distribution. First results of this study will be presented at the conference.
References: [1] Layer, P. (2000) Meteoritics & Planet. Sci, 35, 591–599; [2] Gurov, E.P. et al. (2007), Meteorit. Planet. Sci,42,307–319; [3] Gurov, E.P. & Gurova, E.P. (1991), Nauk.Dumka Press, 160pp.; [4] Ispolatov,V.O. et al., (2004), J. Geol., 112, p.369-377.