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Earth and Space Sciences · Glossary

What is Depleted mantle, enriched mantle?

Also known as: depleted mantle · enriched mantle

Definition 4.6 University Earth and Space Sciences — Year 2 · Chapter 4 — Isotope Geochemistry

A depleted mantle is a part of the mantle that has lost incompatible elements to melts, so that its Sm/Nd is higher and its Rb/Sr lower than chondritic; with time its εNd\varepsilon_{\mathrm{Nd}} becomes positive and its 87Sr/86Sr^{87}\mathrm{Sr}/^{86}\mathrm{Sr} low. An enriched mantle is a part of the mantle that has gained incompatible elements, for instance from recycled crust or from small melts, with a negative εNd\varepsilon_{\mathrm{Nd}} or a high 87Sr/86Sr^{87}\mathrm{Sr}/^{86}\mathrm{Sr}.

Neodymium isotope evolution, as _ Nd, of the chondritic reservoir (zero by definition), of a depleted mantle closed since 4.567\, Ga whose Sm/Nd brings it to the mean MORB today, and of a crust extracted from it 2.7\, Ga ago with the Sm/Nd of the upper continental crust. Each line is nearly straight, as the linear-growth proposition says. Data: CHUR, White’s text; mean MORB, Gale and others (2013); Sm/Nd of the crust, Rudnick and Gao.
Neodymium isotope evolution, as εNd\varepsilon_{\mathrm{Nd}}, of the chondritic reservoir (zero by definition), of a depleted mantle closed since 4.567 Ga4.567\,\mathrm{Ga} whose Sm/Nd brings it to the mean MORB today, and of a crust extracted from it 2.7 Ga2.7\,\mathrm{Ga} ago with the Sm/Nd of the upper continental crust. Each line is nearly straight, as the linear-growth proposition says. Data: CHUR, White’s text; mean MORB, Gale and others (2013); Sm/Nd of the crust, Rudnick and Gao.
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