Constraints on the formation age and evolution of the Moon from 142Nd–143Nd systematics of Apollo 12 basalts

• Published in: Earth and planetary science letters 2014-06, Vol.396, p.179-189
• Main Authors: McLeod, Claire L., Brandon, Alan D., Armytage, Rosalind M.G.
• Format: Article
• Language: English
• Subjects: 142Nd; Age; Apollo mare basalts; Basalt; Closures; Formations; Isotopes; lunar evolution; lunar mantle; magma ocean; Mantle; Moon; Reservoirs
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2014.04.007

The Moon likely formed as a result of a giant impact between proto-Earth and another large body. The timing of this event and the subsequent lunar differentiation timescales are actively debated. New high-precision Nd isotope data of Apollo mare basalts are used to evaluate the Low-Ti, High-Ti and KREEP mantle source reservoirs within the context of lunar formation and evolution. The resulting models are assessed using both reported 146Sm half-lives (68 and 103 Myr). The linear relationship defined by 142Nd–143Nd systematics does not represent multi-component mixing and is interpreted as an isochron recording a mantle closure age for the Sm–Nd system in the Moon. Using a chondritic source model with present day μ142Nd of −7.3, the mare basalt mantle source reservoirs closed at 4.45−09+10 Ga (t1/2Sm146=68 Myr) or 4.39−14+16 Ga (t1/2Sm146=103 Myr). In a superchondritic, 2-stage evolution model with present day μNd142 of 0, mantle source closure ages are constrained to 4.41−08+10 (t1/2Sm146=68 Myr) or 4.34−14+15 Ga (t1/2Sm146=103 Myr). The lunar mantle source reservoir closure ages