Abstract
The relationship between the compositions of the Earth and chondritic meteorites is at the center of many important debates. A basic assumption in most models for the Earth's composition is that the refractory elements are present in chondritic proportions relative to each other. This assumption is now challenged by recent (142)Nd/(144)Nd ratio studies suggesting that the bulk silicate Earth (BSE) might have an Sm/Nd ratio 6% higher than chondrites (i.e., the BSE is superchondritic). This has led to the proposal that the present-day (143)Nd/(144)Nd ratio of BSE is similar to that of some deep mantle plumes rather than chondrites. Our reexamination of the long-lived (147)Sm-(143)Nd isotope systematics of the depleted mantle and the continental crust shows that the BSE, reconstructed using the depleted mantle and continental crust, has (143)Nd/(144)Nd and Sm/Nd ratios close to chondritic values. The small difference in the ratio of (142)Nd/(144)Nd between ordinary chondrites and the Earth must be due to a process different from mantle-crust differentiation, such as incomplete mixing of distinct nucleosynthetic components in the solar nebula.
Highlights
The relationship between the compositions of the Earth and chondritic meteorites is at the center of many important debates
| | | chondrite composition Earth composition midocean ridge basalt | Sm-Nd isotopic system nucleosynthetic anomalies and it has a superchondritic Sm/Nd ratio (∼6% higher than the chondritic value)
The sum of the CC and depleted mantle (DM) is the accessible portion of the bulk silicate Earth (BSE) (7, 16), and it has a superchondritic Sm/Nd ratio
Summary
The relationship between the compositions of the Earth and chondritic meteorites is at the center of many important debates. We use the 147Sm-143Nd isotopic system in MORBs and the CC to test whether the BSE could have a superchondritic 147Sm/144Nd ratio with a present-day «Nd of +7 The 147Sm/144Nd ratio of the DM has previously been estimated by assuming either a chondritic (5, 6) or a superchondritic (13) BSE composition and a mean age of CC extraction (4, 25) that depleted the mantle (1.5–2.2 Ga).
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