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Zircons from nine Palaeoproterozoic granitoid intrusions within the southern part of the Fennoscandian Shield have been studied by laser ablation inductively coupled plasma source mass spectrometry to obtain U-Pb ages (in the range 1.88-1.68 Ga) and Hf isotope compositions. Six granitoids are from the 1.85-1.65 Ga Transscandinavian Igneous Belt; during that period more than 10 6 km 3 of granitoid magma intruded the pre-existing crust. The large majority of magmatic zircons from the nine granitoids have a limited initial range, 176 Hf/ 177 Hf ¼ 0.2816-0.2818, and define an evolutionary trend given by an initial value of å Hf(1:88Ga) % +2 AE 3 at an average 176 Lu/ 177 Hf ¼ 0.015. These data show that a geographically extensive, long-lived, relatively homogeneous, and dominant magma source resided within 2.1-1.86 Ga Svecofennian juvenile crust between 1.88 and 1.68 Ga. Zircon xenocrysts (1.91-1.98 Ga) with initial å Hf ¼ +0 to +2.5 from one of the intrusions provide additional evidence for such a long-lived crustal source of granitic magmas in central Fennoscandia. The granitoids were emplaced during a period of active mafic underplating that supplied heat to the anatectic zone in the lower-middle crust, but little or no mantle-derived Hf to the granitic magmas, in contrast to many mixed intermediate rocks.

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