Origin and transportation history of lunar breccia 14311

Abstract

In this paper, we compare the U-Pb zircon age distribution pattern of sample14311 from the Apollo 14 landing site with those from other breccias collected at the samelanding site. Zircons in breccia 14311 show major age peaks at 4340 and 4240 Ma and smallpeaks at 4110, 4030, and 3960 Ma. The zircon age patterns of breccia 14311 and otherApollo 14 breccias are statistically different suggesting a separate provenance andtransportation history for these breccias. This interpretation is supported by different U-PbCa-phosphate and exposure ages for breccia 14311 (Ca-phosphate age: 3938  4 Ma,exposure age: ~550–660 Ma) from the other Apollo 14 breccias (Ca-phosphate age:3927  2 Ma, compatible with the Imbrium impact, exposure age: ~25–30 Ma). Based onthese observations, we consider two hypotheses for the origin and transportation history ofsample 14311. (1) Breccia 14311 was formed in the Procellarum KREEP terrane by a3938 Ma-old impact and deposited near the future site of the Imbrium basin. The brecciawas integrated into the Fra Mauro Formation during the deposition of the Imbrium impactejecta at 3927 Ma. The zircons were annealed by mare basalt flooding at 3400 Ma atApollo 14 landing site. Eventual ly, at approximately 660 Ma, a small and local impactevent excavated this sample and it has been at the surface of the Moon since this time. (2)Breccia 14311 was formed by a 3938 Ma-old impact. The location of the sample is notknown at that time but at 3400 Ma, it was located nearby or buried by hot basaltic flows.It was transported from where it was deposited to the Apollo 14 landing site by an impactat approximately 660 Ma, possibly related to the formation of the Copernicus crater andhas remained at the surface of the Moon since this event. This latter hypothesis is thesimplest scenario for the formation and transportation history of the 14311 breccia.