Ages determined for magnesian and ferroan anorthosite crustal rock suites overlap, suggesting they formed contemporaneously about 4.3–4.5 Ga. A notable exception is the Sm-Nd age previously determined on Mg-suite gabbronorite 67667 which is at least 100 Ma younger than the youngest ferroan anorthosite. New chronologic measurements of 67667 presented here yield concordant Sm-Nd and Rb-Sr mineral isochron ages of 4349 ± 31 Ma and 4368 ± 67 Ma, suggesting the sample is older than previous estimates. Furthermore, a whole rock Sm-Nd isochron of Mg-suite rocks from the Apollo 14, 15, 16, and 17 landing sites yields an age of 4348 ± 25 Ma, indicating that Mg-suite magmatism was widespread and roughly contemporaneous on the lunar nearside. Here, analysis of Sm-Nd internal isochron ages confirms that Mg-suite magmatism was restricted to a period between about 4.33 and 4.35 Ga at the Apollo 14, 15, 16, and 17 landing sites and was synchronous with magmatism at the Apollo 16 site associated with the ferroan anorthosite suite between 4.35 and 4.37 Ga. Magnesian- and ferroan anorthosite suite rocks with ages younger than ~4.33 Ga appear to have experienced slow cooling in the deep lunar interior, so that the ages record when the samples cooled below the closure temperature of the Sm-Nd isotopic system and not the time they crystallized.
Borg, Lars E., et al. "The formation and evolution of the Moon’s crust inferred from the Sm-Nd isotopic systematics of highlands rocks." Geochimica et Cosmochimica Acta, vol. 290, no. na, Sep. 2020. https://doi.org/10.1016/j.gca.2020.09.013
Borg, Lars E., Cassata, William S., Wimpenny, Josh, Gaffney, Amy M., & Shearer, Charles K. (2020). The formation and evolution of the Moon’s crust inferred from the Sm-Nd isotopic systematics of highlands rocks. Geochimica et Cosmochimica Acta, 290(na). https://doi.org/10.1016/j.gca.2020.09.013
Borg, Lars E., Cassata, William S., Wimpenny, Josh, et al., "The formation and evolution of the Moon’s crust inferred from the Sm-Nd isotopic systematics of highlands rocks," Geochimica et Cosmochimica Acta 290, no. na (2020), https://doi.org/10.1016/j.gca.2020.09.013
@article{osti_1771024,
author = {Borg, Lars E. and Cassata, William S. and Wimpenny, Josh and Gaffney, Amy M. and Shearer, Charles K.},
title = {The formation and evolution of the Moon’s crust inferred from the Sm-Nd isotopic systematics of highlands rocks},
annote = {Ages determined for magnesian and ferroan anorthosite crustal rock suites overlap, suggesting they formed contemporaneously about 4.3–4.5 Ga. A notable exception is the Sm-Nd age previously determined on Mg-suite gabbronorite 67667 which is at least 100 Ma younger than the youngest ferroan anorthosite. New chronologic measurements of 67667 presented here yield concordant Sm-Nd and Rb-Sr mineral isochron ages of 4349 ± 31 Ma and 4368 ± 67 Ma, suggesting the sample is older than previous estimates. Furthermore, a whole rock Sm-Nd isochron of Mg-suite rocks from the Apollo 14, 15, 16, and 17 landing sites yields an age of 4348 ± 25 Ma, indicating that Mg-suite magmatism was widespread and roughly contemporaneous on the lunar nearside. Here, analysis of Sm-Nd internal isochron ages confirms that Mg-suite magmatism was restricted to a period between about 4.33 and 4.35 Ga at the Apollo 14, 15, 16, and 17 landing sites and was synchronous with magmatism at the Apollo 16 site associated with the ferroan anorthosite suite between 4.35 and 4.37 Ga. Magnesian- and ferroan anorthosite suite rocks with ages younger than ~4.33 Ga appear to have experienced slow cooling in the deep lunar interior, so that the ages record when the samples cooled below the closure temperature of the Sm-Nd isotopic system and not the time they crystallized.},
doi = {10.1016/j.gca.2020.09.013},
url = {https://www.osti.gov/biblio/1771024},
journal = {Geochimica et Cosmochimica Acta},
issn = {ISSN 0016-7037},
number = {na},
volume = {290},
place = {United States},
publisher = {Elsevier; The Geochemical Society; The Meteoritical Society},
year = {2020},
month = {09}}
Carlson, Richard W.; Borg, Lars E.; Gaffney, Amy M.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol. 372, Issue 2024https://doi.org/10.1098/rsta.2013.0246