Neodymium Isotope Evidence for a Chondritic Composition of the Moon

Abstract

Samarium-neodymium isotope data for six lunar basalts show that the bulk Moon has a 142 Nd/ 144 Nd ratio that is indistinguishable from that of chondritic meteorites but is 20 parts per million less than most samples from Earth. The Sm/Nd formation interval of the lunar mantle from these data is \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(215_{-21}^{+23}\) \end{document} million years after the onset of solar system condensation. Because both Earth and the Moon likely formed in the same region of the solar nebula, Earth should also have a chondritic bulk composition. In order to mass balance the Nd budget, these constraints require that a complementary reservoir with a lower 142 Nd/ 144 Nd value resides in Earth's mantle.