New evidence for an impact origin of oblong rimmed depressions near Rio Cuarto, Cordoba Province, Argentina, includes shocked silicate phases (e.g., diaplectic glass), thermal decomposition of high-temperature mineral clasts (e.g., baddeleyite from zircon), rapid quenching, very low water contents (≤0.1 wt%), and generation of identical glasses in hypervelocity laboratory impact experiments. The results indicate that glasses with a wide range in major element concentrations can form from a single target type in a relatively small impact event. Impact glasses with the greatest volatile loss typically exhibit the greatest meteoritic contamination (as defined by Cr, Ni, and Ir abundances). The different impact glass types and the different degrees of impactor contamination are proposed to reflect proximity to the projectile-target interface during shallow penetration in an oblique impact, consistent with laboratory simulations and planetary analogues.

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