Samarium-neodymium (Sm-Nd) dating is a process for determining the ages of rocks based on the radioactive decay of two samarium isotopes (Sm-147 and Sm-146) to two neodymium isotopes (Nd-143 and Nd-142 respectively).Sm-147 has a much longer half-life than Sm-146, but the concentration of both of them varies in different rock types, depending on exactly when the rocks crystallized from the parent magma.age relation of multiple geochronological systems [Spear and Parrish, J. 37 (1996) 733-765], a cooling rate of ∼ 15-20°C/Myr seems most reasonable for the Valhalla complex.
In order for the predicted ages to be accurate, however, scientists need sensitive methods for determining the necessary concentrations and ratios, and although several such methods have been developed, there is still room for improvement.
Now, by combining various forms of chromatography, including cation-exchange chromatography, with two different forms of mass spectrometry, two Japanese scientists have created perhaps the most sensitive method yet developed for conducting Sm-Nd dating.
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Thus, the concentration of samarium and neodymium in rocks, and the ratios between different isotopes of neodymium, can reveal how long ago a rock sample crystallized from magma, and thus how old it is.
This process works for rocks on the Earth and also for rocks from other planetary bodies in the solar system, such as the Moon and Mars, as well as for meteorites.
They are thus, theoretically, not particularly susceptible to partitioning during melting of silicate rocks.
Fractional crystallisation of felsic minerals changes the Sm/Nd ratio of the resultant materials.
Using a peak metamorphic P-T condition of 8 ± 1 kbar, 820 ± 30°C [Spear and Parrish, J. 37 (1996) 733-765], the core (67.3 ± 2.3 Ma) and bulk (60.9 ± 2.1 Ma) ages of the British Columbian garnet sample yield a cooling rate of 2-13°C/Myr, which is in very good agreement with the cooling rates that we have derived by modeling the retrograde Fe-Mg zoning in the same garnet, and assuming the same peak metamorphic P-T condition.
Considering earlier cooling rate data derived from closure temperature vs.
The various reservoirs within the solid earth will have different values of initial Nd ratios, especially with reference to the mantle.