Nd ratios in any crustal rock would yield a model age for the formation of that rock (or its precursor) from the chondritic reservoir.This is true, providing that there was sufficient Nd/Sm fractionation during the process of crustal extraction from the mantle to give a reasonable divergence of crustal and mantle evolution lines (Fig. The model age is then given as: might provide a crustal formation age for a wide variety of rocks.However, this sample was by no means representative of the Although Nd model ages are generally applied to dating the time of crustal separation from the mantle, other more specialised applications have been made. (1984) investigated the time of diamond formation in the South African mantle lithosphere by dating garnet inclusions in diamonds.
The initial ratio of Onverwacht lavas is shown for comparison. An important stage in filling this gap was a study on Proterozoic metamorphic basement from the Colorado Front Range (De Paolo, 1981).Four meta-volcanics and two charnockitic granulites from the Idaho Springs Formation were dated by the Sm De Paolo was able to fit a quadratic curve to Idaho Springs and modern island-arc data (Fig.