A record of impacts preserved in the lunar regolith

作者：Shuster David L^*; Balco Greg; Cassata William S; Fernandes Vera A; Garrick Bethell Ian; Weiss Benjamin P

来源：Earth and Planetary Science Letters, 2010, 290(1-2): 155-165.

DOI：10.1016/j.epsl.2009.12.016

• Moon
• lunar impacts
• (40)Ar/(39)Ar thermochronometry
• Apollo
• regolith

The absolute chronology of meteoroid impacts on the Moon is largely quantified by only a few (40)Ar/(39)Ar "plateau ages" of rocks thought to be associated with specific impact events (Stoffler et al., 2006). We demonstrate a more broadly applicable approach by using high-resolution (40)Ar/(39)Ar thermochronometry to investigate the physical conditions responsible for partially reset K-Ar systems in lunar rocks. Seven rocks from Apollo 16 regolith sample 63503 have plateau ages of either 3.9 billion yr (Ga) or 4.2 Ga and all experienced varying degrees of partial resetting. Concordance between diffusion kinetics and the degree of resetting among all samples shows that these observations are best explained by a heating event 3.3 Ga ago that lasted between similar to 10(3) s (at similar to 600 degrees C) and -20 yr (at similar to 300 degrees C). We conclude that partial resetting of the K-Ar systems in these samples record an impact event similar to 3.3 Ga ago that mixed several preexisting ejecta units in the Cayley Plains. If partially reset (40)Ar/(39)Ar ages of other lunar highland samples also constrain the timing of late-stage reheating associated with impact events, they constitute an additional record of impacts preserved in the lunar regolith. A review of existing datasets from this perspective reveals that episodic pulses in the impactor flux in the inner system are common, and most likely related to dynamical events in the asteroid belt or outer Solar System.

• 出版日期2010-2-15