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

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.