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Published September 1996 | public
Journal Article

Sm-Nd systematics of a silicate inclusion in the Caddo IAB iron meteorite


We report the first Sm-Nd data from an iron meteorite silicate inclusion. Mineral separates from an inclusion in the Caddo IAB iron define a ^(147)Sm/^(143)Nd age of 4.53±0.02 Ga, and an initial ^(146)Sm/^(144)Sm of 0.0086±0.0021. A plagioclase separate from the inclusion yields the lowest ^(142)Nd/^(144)Nd ratio measured to date, which provides an absolute maximum initial solar system ϵ_(142) of −2.1 ± 0.4. When the ^(146)Sm/^(142)Nd data are combined with the ^(147)Sm/^(143)Nd data, we obtain our preferred initial solar system ϵ_(142) value of −3.2 ϵu, which corresponds to an initial ^(146)Sm/^(144)Sm of 0.009. Rare earth element data from the Caddo silicate inclusion suggest that it was derived by partial melting of a chondritic source prior to incorporation into the metal. Therefore, differentiation of the silicate portion of the parent body must have started approximately within the first 30 Ma of solar system history. The data reported here clearly show that IAB meteorites preserve a record of very early planetary differentiation processes. Modeling of element diffusion indicates that, if the silicate material was incorporated into its FeNi host at a time much later than 4.53 Ga, then the mixing must have taken place at shallow levels (i.e., < 50 m) in the parent body, in order to preserve the Sm-Nd systematics. It is more likely that incorporation of the silicate took place at depths greater than 2 km, and that it occurred within the first ∼ 30 Ma of solar system history. This is consistent with estimates of cooling rates determined for IAB irons.

Additional Information

© 1996 Elsevier Science B.V. Received 26 February 1996; accepted 26 June 1996. We thank H. Palme and J. Zipfel for discussions and for comments on an earlier version of the manuscript, G. Lugmair and S. Jacobsen for useful reviews of the manuscript, and J.D. Hutcheon for discussions on this work. The Caddo silicate inclusion material was generously provided by H. Palme. This work was supported by NASA Grant NAGW-3337. Division Contribution 5400 (827). [MK]

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