CR-TYPE CHONDRITE FOR AIRBURST EVENT OVER EAST ANTARCTICA 430 KA AGO

Introduction: The geological record contains scarce evidence for airbursts, the most common type of hypervelocity impact events. During airbursts, impactors of 50 to 150 m in size are fragmented and vaporized during atmospheric entry, as exemplified by the Tunguska and Chelyabinsk events [1]. In recent years, meteoritic debris resulting from such low-altitude airbursts has been found on various locations across Antarctica (cf. summary in [2]). Fine-grained (<100 μm) particles recovered from Miller Butte (Northern Victoria Land), Dome Concordia (C), and Dome Fuji (F) were likely produced by a Tunguska-like event 481 ka ago [2]. More recently, larger (~100 to 500 μm) extraterrestrial spherical and spherulitic particles correlated to similar particles in the Dome C and Dome F ice cores, dated to ca. 430 ka, have been recovered from sedimentary deposits near the Walnumfjellet (WN) summit in the Sør Rondane Mts., East Antarctica (S72°07'11", E24°12'30"). The unique properties of the recovered particles attest to an unusual type of touchdown event, likely intermediate between an airburst and a crater-forming impact, during which a high-velocity vapor jet produced by the disruption of a projectile reached the Antarctic ice sheet [2]. Using additional petrographic, geochemical, and isotopic data, we refine the nature of the impactor, the location of the touchdown, and thermodynamic conditions under which the vapor jet interacted with the Antarctic ice.