GROUND TRUTH FOR OBLIQUE IMPACT PROCESSES - NEW INSIGHT FROM THE RIO-CUARTO, ARGENTINA, CRATER FIELD

New evidence for an impact origin of oblong rimmed depressions near Ri o Cuarto, Cordoba Province, Argentina, includes shocked silicate phase s (e.g., dialectic glass), thermal decomposition of high-temperature m ineral clasts (e.g., baddeleyite from zircon), rapid quenching, very l ow water contents (less-than-or-equal-to 0.1 wt%), and generation of i dentical glasses in hypervelocity laboratory impact experiments. The r esults indicate that glasses with a wide range in major element concen trations can form from a single target type in a relatively small impa ct event. Impact glasses with the greatest volatile loss typically exh ibit the greatest meteoritic contamination (as defined by Cr, Ni, and Ir abundances). The different impact glass types and the different deg rees of impactor contamination are proposed to reflect proximity to th e projectile-target interface during shallow penetration in an oblique impact, consistent with laboratory simulations and planetary analogue s.