The Shergotites Are Young

Recently, Bouvier et al. (2006), interpreting their Pb isotopic data, have inferred that the shergottite suite of the SNC (martian) meteorites have ancient ages of approximately 4-4.5 b.y. But conventional wisdom has it that the shergottites are much younger (approximately 500-150 m.y.) Are the shergottites young or are they ancient rocks whose ages have been reset by metamorphism or alteration?