Inferences about magma sources and mantle structure from variations of ^(143)Nd/^(144)Nd

Abstract

Continental flood basalts and mid-ocean ridge (MOR) tholeiitic basalts have distinctly different ^(143)Nd/^(144)Nd which may permit a priori distinction between "continental" and "oceanic" igneous rocks. Initial ^(143)Nd/^(144)Nd of continental igneous rocks through time fall on a Sm/Nd evolution curve with chondritic REE abundance ratio. These observations indicate that many continental igneous rocks are derived from a reservoir with chondritic REE pattern which may represent primary material remaining since the formation of the earth. Oceanic igneous rocks are derived from a different ancient reservoir which has Sm/Nd higher than chondritic. Initial ^(143)Nd/^(144)Nd and ^(87)Sr/^(86)Sr in young basalts from both oceans and continents show a strong correlation suggesting that Sm-Nd and Rb-Sr fractionation events in the mantle may be correlative and caused by the same process. From this correlation Rb/Sr for the earth is inferred to be 0.029.

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© 1976 American Geophysical Union. Received September 30, 1976, accepted November 4, 1976. We thank J. Gittins, T. Simkin, W. S. Baldridge, H. R. Bowman, W. G. Melson, G. Thompson, Tj. H. van Andel, V. Bowen, T. Bence, A. R. McBirney, A. J. Gancarz, L. T. Silver, and G. Goles for providing samples. This work was supported by NASA Grant NGL 05-002-188 and NSF Grant PHY 76-02724.

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