ISOTOPE FRACTIONATION DURING IMPACT: EARTH VS THE MOON

Because the extent of isotope fractionation of many elements, Cu, Zn, and S among them, in lunar soils [1] is very strong (up to 3 per mil per amu) and well beyond what is expected from petrological processes, we investigated the iso-topic effects of a large terrestrial impact. The 49,000-year-old Meteor Crater in Arizona is recent and well suited for this par-ticular study because the composition and the geology of the flat-lying sediments in which the impactor formed a km-size crater are particularly simple [2]. Seven classes of shock features were identified [3] from the pristine rocks (0) to shock melts (6). The respective contribution of the impactor and target rocks to the melts is well understood [4]..