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History of the Pasamonte achondrite: Relative susceptibility of the SmNd, RbSr, and UPb systems to metamorphic events

D.M. Unruh·N. Nakamura·M. Tatsumoto
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Abstract

The Rb Sr, Sm Nd, and U Pb systematics of the eucrite Pasamonte have been studied in order to investigate the relative susceptibility of the different systems to post-crystallization events and to determine the age and history of the meteorite. The Rb Sr and 238 U- 206 Pb data of mineral separates do not define an isochron but the Sm Nd data define an internal isochron which corresponds to the formation age of 4.58 ± 0.12b.y. (10 9 years). The 207 Pb- 206 Pb data of mineral separates define an apparent age of 4.53 ± 0.03b.y. , however we conclude that this age, while in agreement with the Sm Nd age, is not strictly valid since the U Pb data indicate at least three stages of evolution. The U Pb data indicate that the parent body of the meteorite experienced brecciation shortly after the formation of the parent body surface ( ∼4.2–4.45b.y. ago) and a recent disturbance (collision?) 6 ± 30m.y. ago. The latter age is within the range of cosmic ray exposure ages for achondrites.

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D.M. Unruh, N. Nakamura, M. Tatsumoto. 1977. History of the Pasamonte achondrite: Relative susceptibility of the SmNd, RbSr, and UPb systems to metamorphic events. https://doi.org/10.1016/0012-821x(77)90141-8

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