[PPS10-P19] Variations in Shock Deformation of Feldspars in Three Achondrites: NWA 2727 Lunar breccia, NWA 856 Shergottite and NWA 3117 Howardite.
Keywords:Howardite, Shergottite, Lunar breccia, Shock deformation, Feldspar, EPMA Analysis
The high deformation of NWA 856 is expected because this sample is from Mars, which is a large parent body and requires a powerful impact to accelerate a rock to escape velocity. In contrast, the parent body of NWA 3117 (Vesta) is smaller than that of NWA 2727 (the Moon), yet NWA 3117 appears more highly deformed than NWA 2727. One possible explanation is that NWA 2727 is from a relatively young part of the Moon, which has not been exposed to impacts as long as the surface of Vesta. My EPMA analyses of pyroxenes show that Mn/Fe ratios are highest in NWA 3117, lower in NWA 856, and lowest in NWA 2727, and are consistent with classification of these meteorites as a howardite (parent body Vesta), shergottite (Mars), and lunar meteorite (Moon), respectively. The higher volatility of Mn vs. Fe suggests that the observed variations in Mn/Fe could result from parent body formation at temperatures that were highest for the Moon, lower for Mars, and lowest for Vesta. However, variations in oxygen fugacity and other parameters may also have affected Mn/Fe.