Impact-related thermal effects on the redox state of Ca-pyroxene

Oxidation is observed in Ca-pyroxene subjected to a range of shock pressures (2159 GPa). Changes in the pyroxene redox ratio as measured by the changes in % Fe3+ ranged from 2-6 times the starting composition. M_ ossbauer and reflectance spectroscopy record the changing Fe3+ concentration as a preferential oxidation of Fe2+ in the M-2 crystallographic site. The oxidation is also accompanied by mechanical changes in the pyroxene crystals including fracturing, linear defects, and twinning. As oxygen fugacity is often calculated using mineral redox ratios and thought to represent the prevailing fO(2) during crystallization, it is imperative to recognize that the fO(2) values measured in impactderived materials may represent that of the impact and not the magma source region.