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Thus, ultramafic rocks have low Sm and Nd and Sm/Nd ratios (komatiite has 1.14ppm Sm and 3.59ppm Nd versus 4.65ppm Sm and 21.6ppm Nd in rhyolite).
Through the analysis of isotopic compositions of neodymium, De Paolo and Wasserburg first discovered that terrestrial igneous rocks closely followed the Chondritic Uniform Reservoir (CHUR) line.
The importance of this process is apparent in modeling the age of continental crust formation.
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.
Nd isotope ratios are used to provide information on the source of igneous melts as well as to provide age data.
Thus, ultramafic rocks have high Sm and low Nd and therefore high Sm/Nd ratios.
Felsic rocks have low concentrations of Sm and high Nd and therefore low Sm/Nd ratios (komatiite has 1.14 parts per million (ppm) Sm and 3.59 ppm Nd versus 4.65 ppm Sm and 21.6 ppm Nd in rhyolite).
The usefulness of Sm-Nd dating is the fact that these two elements are rare earths.
Thus, as a rock 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.
The intersection between these two evolution lines then indicates the crustal formation age.