Sm nd isotopic dating

The concentration of Sm and Nd in silicate minerals increase with the order in which they crystallise from a magma according to Bowen's reaction series.

Samarium is accommodated more easily into mafic minerals, so a mafic rock which crystallises mafic minerals will concentrate neodymium in the melt phase faster relative to samarium.

Also, the crust that is formed from this melt will be enriched in REE's.

Neodymium is also a light REE, and also common in peridotitic minerals such as plagioclase and pyroxene. This equation is easily derived by dividing eqn 1 (above) by the stable Neodymium counterpart of the same form: Eqn 2: This ratio is used to determine the crustal model age of the sampled rock.

The two elements are joined in a parent-daughter relationship by the alpha-decay of Nd ratio of the isotope system provides important information on crustal formation and the isotopic evolution of the solar system.Neodymium isotopes are a common daughter product of the decay of Samarium, a rare earth element (REE).REE's are extremely concentrated in melt compared to the concentration of them in mineral form.Model ages of formation of crust are based on the depleted mantle curve (from Bennet and De Paulo, 1987): CF=crustal formation The depleted mantle curve is described by: Eqn 4.Thus, E values can be extrapolated back to the depleted mantle curve to determine the age that the crust formed and the Neodymium was placed in crystal form.Through the analysis of isotopic compositions of neodymium, De Paolo and Wasserburg discovered that terrestrial igneous rocks closely followed the Chondritic Uniform Reservoir (CHUR) line.

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