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Research Article |
1 Department of Geosciences, University of Oslo, PO Box 1047 Blindern, N-0316 Oslo, Norway
2 Naturhistoriska Riksmuseet, PO Box 50 007, SE-104 05 Stockholm, Sweden
3 Present address: Rio Tinto T&I, 1 Research Avenue, Bundoora 3083, Victoria, Australia
4 Institute for Energy Technology, PO Box 40, N-2027 Kjeller, Norway
5 Present address: Bayerische Staatssammlung für Paläontologie und Geologie, Richard Wagner Strasse 10, DE-80 833 München, Germany
*Corresponding author (e-mail: tom.andersen{at}geo.uio.no)
Supplementary material: U–Pb analyses, age calculations and Lu–Hf data are available at http://www.geolsoc.org.uk/SUP18330.
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 106 km3 of granitoid magma intruded the pre-existing crust. The large majority of magmatic zircons from the nine granitoids have a limited initial range, 176Hf/177Hf = 0.2816–0.2818, and define an evolutionary trend given by an initial value of 
Hf(1.88Ga) 
+2 ± 3 at an average 176Lu/177Hf = 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 Hf = +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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  T. Andersen, S. Graham, and A. G. Sylvester THE GEOCHEMISTRY, Lu-Hf ISOTOPE SYSTEMATICS, AND PETROGENESIS OF LATE MESOPROTEROZOIC A-TYPE GRANITES IN SOUTHWESTERN FENNOSCANDIA Can Mineral, 2009; 47: 1399 - 1422. [Abstract] [Full Text] [PDF]
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