The Sm-Nd isotopic method in the geochronology laboratory of the University of Brasilia

Nd isotopes represent one of the best tools to investigate the processes in volved in the evolution of the continental crust and mantle. This is due ma inly to the similar geochemical behaviour of Sm and Nd, both light rare ear th elements, which inhibits their fractionation during most varied geologic al processes. In order to carry out crustal evolution studies in central Br azil, the Sm-Nd isotopic method was implanted at the Geochronology Laborato ry of the University of Brasilia. The Sm-Nd separation methodology is basic ally that described in Richard et al. (1976), with the addition of some imp rovements. In this study we describe in detail the methodology used in Bras ilia. Precision and accuracy were checked with the international standards such as JB-3, BCR-1, BHVO-1 and La Jolla, and the following results were fo und: JB-3 (Nd=15.74 ppm and Sm=4.28 ppm), BCR-1 (Nd-143/Nd-144=0.512647+/-8 , Nd=28.73 ppm and Sm=6.66 ppm), BHVO-1 (Nd=24.83 ppm and Sm=6.2 ppm) and L a Jolla (Nd-143/Nd-144=0.511835+/-14).