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Samarium–neodymium dating
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<p>Samarium–neodymium dating is a <a href="/facts/Radiometric_dating/bDFjdPqV">radiometric dating</a> method useful for determining the ages of <a href="/facts/Rock_(geology)/FXCJkmop">rocks</a> and <a href="/facts/Meteorite/NsmHlBlX">meteorites</a>, based on the <a href="/facts/Alpha_decay/rCsHNIUE">alpha decay</a> of the long-lived <a href="/facts/Samarium/09K3kl93">samarium</a> <a href="/facts/Isotope/KD9B1y6o">isotope</a> (147Sm) to the stable <a href="/facts/Radiogenic/KXP6MKk6">radiogenic</a> <a href="/facts/Neodymium/GzDkTIoI">neodymium</a> isotope (143Nd). Neodymium isotope ratios together with samarium–neodymium ratios are used to provide information on the age and source of <a href="/facts/Igneous/xeMJhUah">igneous</a> melts. It is sometimes assumed that at the moment when <a href="/facts/Crust_(geology)/FYG1kP4F">crustal</a> material is formed from the <a href="/facts/Mantle_(geology)/RpDdtjCr">mantle</a> the neodymium isotope ratio depends only on the time when this event occurred, but thereafter it evolves in a way that depends on the new ratio of samarium to neodymium in the crustal material, which will be different from the ratio in the mantle material. Samarium–neodymium dating allows the determination of when the crustal material was formed. </p><p>The usefulness of Sm–Nd dating stems from the fact that these two elements are <a href="/facts/Rare_earths/PQSUQumk">rare earth elements</a> and are thus, theoretically, not particularly susceptible to partitioning during <a href="/facts/Sedimentation/qUgHGvhd">sedimentation</a> and <a href="/facts/Diagenesis/F1nATwdp">diagenesis</a>. <a href="/facts/Fractional_crystallization_(geology)/45jl1eV7">Fractional crystallisation</a> of <a href="/facts/Felsic/0jpm1eSA">felsic</a> minerals changes the Sm/Nd ratio of the resultant materials. This, in turn, influences the rate at which the 143Nd/144Nd ratio increases due to production of radiogenic 143Nd. </p><p>In many cases, Sm–Nd and <a href="/facts/Rubidium%E2%80%93strontium_dating/F1NA2T58">Rb–Sr</a> isotope data are used together. </p>