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They have relatively homogeneous trace-element signatures, and therefore their isotopic evolution can model the evolution of the whole Solar system and of the "bulk Earth".After plotting the ages and initial Nd ratios of terrestrial igneous rocks on a Nd evolution vs.Felsic rocks have low concentrations of Sm and high Nd and therefore low Sm/Nd ratios (for example 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).

De Paolo (1981) argued that these TDM model ages would yield a more accurate age for crustal formation ages than TCHUR model ages – for example, an anomalously low TCHUR model age of 0.8 Gy from Mc Culloch and Wasserburg's Grenville composite was revised to a TDM age of 1.3 Gy, typical for juvenile crust formation during the Grenville orogeny.

Using the above data in conjunction with the Nd diffusion data from [2] and Hf diffusion data from our recent study, we obtain closure temperatures for the Lu-Hf and Sm-Nd decay systems in garnet of ~545-565 °C and 415-430 °C, respectively.

Results from analytical solutions [3, 4] and a more flexible numerical method are found to be in good agreement with one another.

Nd ratios of the samples analyzed are plotted on a ɛNd versus time diagram shown in the figure.

De Paolo (1981) fitted a quadratic curve to the Idaho Springs and average ɛNd for the modern oceanic island arc data, thus representing the neodymium isotope evolution of a depleted reservoir.

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