| 1. |
- Nemchin, Alexander, et al.
(författare)
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Pb-Pb ages of feldspathic clasts in two Apollo 14 breccia samples
- 2017
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 217, s. 441-461
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Tidskriftsartikel (refereegranskat)abstract
- Pb-Pb isochron ages of ca. 3.92 Ga for three K-feldspar-rich clasts from Apollo 14 breccias 14303 and 14083 were determinedusing Secondary Ion Mass Spectrometry (SIMS). These ages are interpreted to represent the resetting of the U-Pb systemin the clasts as a result of brecciation during the Imbrium impact. One of the clasts contains zircon grains that record asignificantly older crystallization age (ca. 4.33–4.35 Ga) for the rock represented by that clast. Initial Pb compositions determinedfor the clasts, combined with the previously measured Pb isotopic compositions of K-feldspar grains from severalApollo 14 breccia samples, constrain a range of initial Pb compositions in the ca. 3.9 Ga Fra Mauro formation at the Apollo14 landing site. This range in initial Pb compositions indicates that the rocks represented by these clasts, or the sources ofthose rocks, evolved with a high 238U/204Pb (µ-value) for substantial periods of time, although the precise crystallization agesof the rocks represented by at least two of the clasts investigated here are unknown.
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| 2. |
- Demidova, S. I., et al.
(författare)
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A micrometeorite from a stony asteroid identified in Luna 16 soil
- 2022
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 6:5, s. 560-567
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Tidskriftsartikel (refereegranskat)abstract
- Despite the intense cratering history of the Moon, very few traces of meteoritic material have been identified in the more than 380 kg of samples returned to Earth by the Apollo and Luna missions. Here we show that an ~200-µm-sized fragment collected by the Luna 16 mission has extra-lunar origins and probably originates from an LL chondrite with similar properties to near-Earth stony asteroids. The fragment has not experienced temperatures higher than 400 °C since its protolith formed early in the history of the Solar System. It arrived on the Moon, either as a micrometeorite or as the result of the break-up of a bigger impact, no earlier than 3.4 Gyr ago and possibly around 1 Gyr ago, an age that would be consistent with impact ages inferred from basaltic fragments in the Luna 16 sample and of a known dynamic upheaval in the Flora asteroid family, which is thought to be the source of L and LL chondrite meteorites. These results highlight the importance of extra-lunar fragments in constraining the impact history of the Earth–Moon system and suggest that material from LL chondrite asteroids may be an important component.
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