Pinpointing the Source of a Lunar Meteorite: Implications for the Evolution of the Moon

Abstract

The lunar meteorite Sayh al Uhaymir 169 consists of an impact melt breccia extremely enriched with potassium, rare earth elements, and phosphorus [thorium, 32.7 parts per million (ppm); uranium, 8.6 ppm; potassium oxide, 0.54 weight percent], and adherent regolith. The isotope systematics of the meteorite record four lunar impact events at 3909 +/- 13 million years ago (Ma), approximately 2800 Ma, approximately 200 Ma, and <0.34 Ma, and collision with Earth sometime after 9.7 +/- 1.3 thousand years ago. With these data, we can link the impact-melt breccia to Imbrium and pinpoint the source region of the meteorite to the Lalande impact crater.

The comparative behavior of apatite‐zircon U‐Pb systems in Apollo 14 breccias: Implications for the thermal history of the Fra Mauro Formation

“…Based on these data the most recently proposed age for the Imbrium impact is defined as 3.85 ± 0.02 Ma (Wilhelms 1987;Ryder 1990Ryder , 1994Spudis 1993;Hartmann et al 2000;Stöffler and Ryder 2001). This age is clearly younger than both 3909 ± 13 Ma and 3926 ± 3 Ma suggested, respectively, by zircon (Gnos et al 2004) and apatite data (this work). However, recalculation of Ar-Ar age using decay constant suggested by Min et al (2000) will result in about 1% increase in the Ar-Ar age, making it similar within the errors to the age estimated from the zircon (Gnos et al 2004) and apatite analyses.…”

“…This age is clearly younger than both 3909 ± 13 Ma and 3926 ± 3 Ma suggested, respectively, by zircon (Gnos et al 2004) and apatite data (this work). However, recalculation of Ar-Ar age using decay constant suggested by Min et al (2000) will result in about 1% increase in the Ar-Ar age, making it similar within the errors to the age estimated from the zircon (Gnos et al 2004) and apatite analyses. Nevertheless, this recalculation does not solve a discrepancy between U-Pb and Rb-Sr data.…”

“…3.9 Ga ages in the overall population of zircons analyzed in lunar samples (Meyer et al 1996;Nemchin et al 2008). A rare exception is the group of grains investigated by Gnos et al (2004) in the impact melt preserved in the lunar meteorite Sayh al Uhaymir (SAU) 169. This group defined an average 207 Pb/ 206 Pb age of 3909 ± 13 Ma.…”

Petrography, mineralogy, and geochemistry of lunar meteorite Sayh al Uhaymir 300

“…It has a strong link to the Imbrium basin and was inferred to have been derived from the Lalande impact crater (Gnos et al 2004). Two other feldspathic breccias, Y-983885 and Calcalong Creek, are relatively rich in Th (2 and 4 ppm, respectively).…”

“…Lunar meteorite SaU 169 is an impact-melt breccia that is extremely enriched with K, REEs, and P (Th 33 ppm, U 8.6 ppm, K 2 O 0.54 wt%), (Gnos et al 2004). It has a strong link to the Imbrium basin and was inferred to have been derived from the Lalande impact crater (Gnos et al 2004).…”