40Ar/39Ar dating of microgram feldspar grains from the paired feldspathic achondrites GRA 06128 and 06129

40Ar/39Ar ages of single feldspar grains from the paired meteorites Graves Nunatak 06128 (GRA8; 8 grains) and 06129 (GRA9; 26 grains) are presented. Plateau ages (⩾70% of the 39Ar released) ranged from 4000 to 4600Ma with an average 1-σ uncertainty of ±90Ma. The most precise ages obtained were 4267±17Ma for a grain from GRA8 and 4437±19Ma and 4321±18Ma for two grains from GRA9. Isotope correlation diagrams yield less precise ages ranging from 3800 to 5200Ma with an average 1-σ uncertainty of 250Ma; they indicate a negligible trapped component. Plateau ages, integrated total fusion ages, and isochron ages are internally concordant at the 95% confidence level.