NEODYMIUM ISOTOPE SYSTEMATICS OF THE MANTLE BENEATH THE BALTIC SHIELD- EVIDENCE FOR DEPLETED MANTLE EVOLUTION SINCE THE ARCHEAN

More than 300 published and unpublished Nd isotopic analyses of mantle derived rocks from the Baltic shield have been compiled. The rocks ra nge in age from Archaean to Phanerozoic. Within any given age-interval , the mantle derived rocks range in epsilon(Nd)(t) from depleted mantl e values at or above the growth curves of the global depleted mantle r eservoirs of DePaolo ( 1981) and DePaolo et al. (1991) to negative val ues. Initial neodymium isotopic compositions below the De Paolo curve are best explained by interaction between depleted mantle derived magm as and local crustal contaminants. The data now available lend no supp ort to the existence of isolated, less depleted or undepleted mantle d omains beneath the Baltic Shield, as was suggested by Mearns et al. (1 986) and Valbracht (1991a, b).