Granites and early Proterozoic crystal evolution in Sweden: Evidence from Sm-Nd, U-Pb and o isotope systematics

U-Pb zircon and whole-rock Rb-Sr, Sm-Nd and O isotope results are reported for granitoids from three Proterozoic provinces in Sweden that represent different crustal environments. The radiometric ages span the period 1.89-1.65 Ga and record events ranging from original igneous crystallisation to late metamorphic resetting. These events occured at different times in the crustal segments. The O isotope ratios identify different crustal source materials for the granitoids. The Sm-Nd results indicate that the major crustal source components common to most of the granitoids formed shortly before 1.9 Ga, close in time of the formation of the earliest granitoids. Contributions from recycled Archaean basement are minimal. The geographically widespread occurrence of such crustal sources indicates that the period around 2 Ga was of great importance for the growth of new continental crust in Sweden. (orig.)