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Sm nd dating method
Samarium-neodymium dating is useful for determining the age relationships of rocks and meteorites, based on radioactive decay of a long-lived samarium (Sm) isotope to a radiogenic neodymium (Nd) isotope.Nd isotope ratios are used to provide information on the source of igneous melts as well as to provide age data.
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.
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.
Thus, as a melt undergoes fractional crystallization from a mafic to a more felsic composition, the abundance of Sm and Nd changes, as does the ratio between Sm and Nd.
Thus, ultramafic rocks have high Sm and low Nd and therefore high Sm/Nd ratios.