Redistribution of Radiogenic Lead in Plagioclase during Shock Metamorphism

Misawa, K.; Yamazaki, F.; Sawada, S.; Sekine, Toshimori

doi:10.1007/978-1-4613-0011-3_7

Cited by 1 publication

(2 citation statements)

References 27 publications

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“…However, Papike et al (1982) noted that the soil at the Apollo 17 Station 8 site had high Sm and Nd abundances, which could also influence the linearity of the 78238 Sm-Nd isochron if the soil were only incorporated into the plagioclase fractions in large quantity. Because the 78238 Sm-Nd isochron does not show evidence for soil addition into the plagioclase fractions it is likely that insufficient soil was added to influence the Sm-Nd isotopic composition of the plagioclase fractions (e.g., the Nd/Pb of the soil is too low), the soil added had a nearly identical Sm-Nd isotopic signature as the plagioclase fractions of 78238, or the high 207 Pb/ 206 Pb component added was elemental Pb mobilized by impact volatility (e.g., Misawa et al, 2000). There is no apparent disturbance to the Pb isotopic systematics of the mafic silicate and whole rock fractions.…”

Section: U-pb Isotopesmentioning

confidence: 98%

“…7a (after Tera and Wasserburg, 1972;Premo et al, 1999). Incorporation of a component with a high 207 Pb/ 206 Pb ratio, such as lunar soil Pb, could occur during the shock event(s) that melted the plagioclase in 78238 (e.g., Misawa et al, 2000). However, Papike et al (1982) noted that the soil at the Apollo 17 Station 8 site had high Sm and Nd abundances, which could also influence the linearity of the 78238 Sm-Nd isochron if the soil were only incorporated into the plagioclase fractions in large quantity.…”

Section: U-pb Isotopesmentioning

confidence: 99%

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A combined Sm–Nd, Rb–Sr, and U–Pb isotopic study of Mg-suite norite 78238: Further evidence for early differentiation of the Moon

Edmunson

Borg

Nyquist

et al. 2009

Geochimica et Cosmochimica Acta

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Lunar Mg-suite norite 78238 was dated using the Sm-Nd, Rb-Sr, and U-Pb isotopic systems in order to constrain the age of lunar magma ocean solidification and the beginning of Mg-suite magmatism, as well as to provide a direct comparison between the three isotopic systems. The Sm-Nd isotopic system yields a crystallization age for 78238 of 4334 ± 37 Ma and an initial e 143 Nd value of À0.27 ± 0.74. The age-initial e 143 Nd (T-I) systematics of a variety of KREEP-rich samples, including 78238 and other Mg-suite rocks, KREEP basalts, and olivine cumulate NWA 773, suggest that lunar differentiation was completed by 4492 ± 61 Ma assuming a Chondritic Uniform Reservoir bulk composition for the Moon. The Rb-Sr isotopic systematics of 78238 were disturbed by post-crystallization processes. Nevertheless, selected data points yield two Rb-Sr isochrons. One is concordant with the Sm-Nd crystallization age, 4366 ± 53 Ma. The other is 4003 ± 95 Ma and is concordant with an Ar-Ar age for 78236. The 207 Pb-206 Pb age of 4333 ± 59 Ma is concordant with the Sm-Nd age. The U-Pb isotopic systematics of 78238 yield linear arrays equivalent to younger ages than the Pb-Pb system, and may reflect fractionation of U and Pb during sample handling. Despite the disturbed nature of the U-Pb systems, a time-averaged l ( 238 U/ 204 Pb) value of the source can be estimated at 27 ± 30 from the Pb-Pb isotopic systematics. Because KREEP-rich samples are likely to be derived from source regions with the highest U/Pb ratios, the relatively low l value calculated for the 78238 source suggests the bulk Moon does not have an exceedingly high l value.

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Section: U-pb Isotopesmentioning

confidence: 98%