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Published May 1974 | Published
Journal Article Open

Evidence for late formation and young metamorphism in the Achondrite Nakhla

Abstract

We have determined an age T=1.37 AE for Nakhla and an initial ^(87)Sr/^(86)Sr, I = 0.7023. A rather thorough Sr equilibration took place at this time between all the phases of this meteorite, but there is clear evidence of somewhat incomplete isotopic equilibrium during the 1.37 AE event, which is not consistent with the derivation of Nakhla from a magma at this time. Nakhla has a young model age of 3.6-2.9 AE which requires that gross differentiation processes for its parent body occur between 3.6 and 1.37 AE, significantly later than 4.6 AE. The most reasonable model is that Nakhla formed as an igneous rock at ∼3 AE and was metamorphosed at 1.37 AE. Several similarities exist between the Nakhla parent planet and the Earth and indicate the existence of other objects with close terrestrial chemical affinities.

Additional Information

Copyright © 1974 by the American Geophysical Union. (Received April 15, 1974; accepted April 24, 1974.) The sample from the Harvard collection was provided through the generous courtesy of Professor C. Frondel with prompting from Judith Frondel. We thank R. A. Schmitt for stimulating our interest in Nakhla in a Mexican restaurant and for providing us with a sample. A. L. Albee provided incisive comments at a critical stage of this paper. This work was supported by the National Science Foundation, Grant GP 28027.

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August 19, 2023
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