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In addition, epsilon units will normalize the initial ratios to CHUR, thus eliminating any effects caused by various analytical mass fractionation correction methods applied.
Neodymium isotope ratios together with samarium-neodymium ratios are used to provide information on the source of igneous melts, as well as to provide age information.
It is sometimes assumed that at the moment when crustal material is formed from the mantle 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.
After plotting the ages and initial Nd ratios of terrestrial igneous rocks on a Nd evolution vs.
time diagram, De Paolo and Wasserburg determined that Archean rocks had initial Nd isotope ratios very similar to that defined by the CHUR evolution line.