Lu-Hf zircon evidence for rapid lunar differentiation

Zircons from the Apollo 14 polymict breccias 14304,14305, and 14321 crystallized from highly incompatible-trace-element enriched sources over an extended period of early lunar history from 4.4 to 4.0 Ga. These zircons contain the least radiogenic (176)Hf/(177)Hf yet observed in lunar samples, consistent with their source magmas containing a component (KREEP) that evolved during chemical differentiation of a global lunar magma ocean. The initial (176)Hf/(177)Hf isotopic compositions of the zircons as a function of their crystallization ages suggest separation of the KREEP source, and thus crystallization of the lunar magma ocean, by similar to 4.48 Ga to no later than 4.38 Ga. (C) 2008 Elsevier B.V. All rights reserved.