Chemistry of Proterozoic orogenic processes at a continental margin in northern Sweden

Sm-Nd isotopic, major-, trace- and rare-earth-element data for two separate age groups of plutonic rocks have been used to characterize early Proterozoic crust formation mechanisms in the vicinity of the exposed Archaean of northern Sweden. The granitoid rocks of the older (1.89–1.87 Ga) group show calc-alkaline trends (diorite-quartz monzonite-adamellite) and have negative ϵ Nd-values ranging from about −8 to −5. They represent variable contamination of isotopically juvenile mantle melts with Archaean crustal material. The younger (1.80 Ga) group of plutonic rocks are of true granitic composition. They show a restricted range of ϵ Nd-values which is encompassed by those of the older group. Trace- and major-element data are consistent with the derivation of the younger group of rocks by remobilization of the earlier formed Proterozoic continental crust. This is in contrast to the temporally similar but isotopically more juvenile granitoids of the Skellefte district to the south.