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Sm-Nd age of the Stillwater complex and the mantle evolution curve for neodymium

DePaolo, D. J. and Wasserburg, G. J. (1979) Sm-Nd age of the Stillwater complex and the mantle evolution curve for neodymium. Geochimica et Cosmochimica Acta, 43 (7). pp. 999-1008. ISSN 0016-7037. doi:10.1016/0016-7037(79)90089-9.

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An internal isochron determined for a gabbro from the Stillwater complex by the Sm-Nd method yields a precise age of 2701 ± 8 Myr and initial ^(143)Nd/^(144)Nd = 0.508248 ± 12. The initial is close to the CHUR evolution curve but clearly displaced below it by ϵ_(Nd) = −2.8 ± 0.2. A spectrum of total rocks in the Stillwater complex ranging from anorthosite to pyroxenite were found to lie on the same isochron to within experimental error indicating the same age and initial. These data demonstrate that some ancient mantle-derived rocks have initial ^(143)Nd/^(144)Nd which deviate substantially from the CHUR evolution curve at the time of their formation. This implies that there was early layering in the mantle with substantial REE fractionation (~6–12% Nd/Sm enrichment) or that the Stillwater complex was highly contaminated with REE from much older continental crust during emplacement. The results show the necessity of high-precision ages and initial ^(143)Nd/^(144)Nd values in order to properly describe REE fractionation in the mantle. While the Sm-Nd age results show no indication of any irregularities, we have confirmed that the Rb-Sr data for the Stillwater are highly disturbed. This comparison indicates that the Sm-Nd parent-daughter system may be much less susceptible to element redistribution during metamorphism, therefore permitting wide application of this technique to rocks of complex histories.

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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 1979 Pergamon Press Ltd. Received 8 December 1978; accepted in revised form 28 February 1979. This paper is dedicated to the memory of E. D. JACKSON who contributed greatly to the knowledge of the Stillwater complex and many other aspects of volcanology and petrology. STEWART MCCALLUM and LINDA RAEDEKE are sincerely thanked for sharing their knowledge of Stillwater complex geology, for providing samples, and for the hospitality of Camp Yorick. We thank the Anaconda Company for access to the Mountain View area. L T. SILVER kindly provided the Sierra Ancha sample. This work was supported by NSF grants EAR76-22494 and EAR78-12966.
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Issue or Number:7
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Official Citation:D.J. DePaolo, G.J. Wasserburg, Sm-Nd age of the Stillwater complex and the mantle evolution curve for neodymium, Geochimica et Cosmochimica Acta, Volume 43, Issue 7, July 1979, Pages 999-1008, ISSN 0016-7037, (
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ID Code:42030
Deposited On:23 Oct 2013 22:48
Last Modified:10 Nov 2021 04:37

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