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Published May 1976 | Published
Journal Article Open

Nd isotopic variations and petrogenetic models


The decay of ^(147)Sm to ^(143)Nd allows ^(143)Nd/^(144)Nd to be used to trace Sm/Nd fractionation in long time-scale geologic processes. ^(143)Nd/^Nd(144) has been measured in terrestrial rock samples of different ages to establish the characteristics of Nd isotopic evolution in the crust and mantle. The evolution of ^(143)Nd/^(144)Nd in the mantle indicates Sm/Nd essentially equal to that of chondrites, and implies a chondritic REE distribution for the earth. Variations in ^(143)Nd/^(144)Nd do exist in the mantle, however, indicating Sm/Nd heterogeneity and the existence of distinct mantle reservoirs with characteristic ^(143)Nd/^(144)Nd. ^(143)Nd/^(144)Nd in average crustal rocks today is much lower than found in recent mantle samples and reflects their age and low Sm/Nd. Oceanic tholeiites and alkali basalt are derived from sources with Sm/Nd which has been 5-10% greater than chondritic over the age of the earth. Alkali basalt can not be derived from mantle reservoirs which have been light REE-enriched for long times.

Additional Information

© 1976 American Geophysical Union. Received March 22, 1976; accepted April 9, 1976. We thank W. G. Melson, P. Vogt, G. Thompson, and L.A. Haskin for providing samples and K. Gschneider for providing high purity Nd metal (normal NN2). Technical assistance and advice from D. A. Papanastassiou, D. Curtis, and F. Tera were invaluable and are gratefully acknowledged. DJD would like to thank Arden Albee for steering him in the direction of this work. Precise Pb isotopic work by A.J. Gancarz (Gancarz, Tera, and Wasserburg, 1975) assured us of the antiquity of the Greenlands ample collected by project Oldstone. This work represents a return to a problem first attempted using Rb-Sr by Paul W. Gast (Gast, 1955, 1960). This work was supported in part by NSF NPS 71-02670 AO5 and NASA NGL 05002188. An outline of these results was Published in EOS (DePaolo and Wasserburg, 1976). Comments on our Cryptography by cognizant colleagues, A.L. Albee, A. J. Gancarz, D . A. Papanastassiou and S. Jacobsen are hereby acknowledged. We appreciate the comments of G. Lugmair and his courtesy in making the revised Juvinas data available. This is contribution No. 2730 of the Div. of Geological and Planetary Sciences.

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August 19, 2023
August 19, 2023