Shock metamorphism investigations of quartz grains in clasts from impact breccia of the Eyreville B drill core, Chesapeake Bay impact structure, USA

The Chesapeake Bay impact structure, approximately 85km in diameter, has been drilled in 2005-2006 at Eyreville (Virginia, USA), to a total depth of 1766m. In the drill cores, the abundance of shock metamorphosed material is very variable with depth. Shocked mineral and lithic clasts, as well as melt particles, are most abundant in suevitic impact breccia section (1397-1451m depth). Shocked quartz (i.e., quartz grains with planar fractures and/or planar deformation features) and melt particles, although rare, are also dispersed in the Exmore Formation unit (444-867m depth). Other lithologies in the Eyreville drill cores show no clear evidence of shock metamorphism. Here, we report on the investigations of 40 samples from the impact breccia section. A total of more than 27,000 quartz grains were examined in about 200 clasts. The abundance of highly shocked clasts tends to decrease with increasing depth. Crystalline clasts derived from the crystalline basement are commonly only slightly shocked (contain generally