Mid-Proterozoic Magmatic Arc Evolution at the Southwest Margin of the Baltic Shield$
Lithos 73 (2004) 289–318 www.elsevier.com/locate/lithos Mid-Proterozoic magmatic arc evolution at the southwest margin of the Baltic Shield$ T. Andersena,b,*, W.L. Griffinb, S.E. Jacksonb, T.-L. Knudsenc, N.J. Pearsonb a Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, N-0316 Oslo, Norway b GEMOC Key Centre, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia c Geological Museum, P.O. Box 1172 Blindern, N-0318 Oslo, Norway Received 29 January 2003; accepted 9 December 2003 Abstract Mid-Proterozoic calc-alkaline granitoids from southern Norway, and their extrusive equivalents have been dated by LAM- ICPMS U–Pb on zircons to ages ranging from 1.61 to 1.52 Ga; there are no systematic age differences across potential Precambrian terrane boundaries in the region. U–Pb and Lu–Hf data on detrital zircons from metasedimentary gneisses belonging to the arc association show that these were mainly derived from ca. 1.6 Ga arc-related rocks. They also contain a minor but significant fraction of material derived from (at least) two distinct older (1.7–1.8 Ga) sources; one has a clear continental signature, and the other represents juvenile, depleted mantle-derived material. The former component resided in granitoids of the Transscandinavian Igneous Belt, the other in mafic rocks related to these granites or to the earliest, subduction-related magmatism in the region. Together with published data from south Norway and southwest Sweden, these findings suggest that the western margin of the Baltic Shield was the site of continuous magmatic arc evolution from at least ca 1.66 to 1.50 Ga.
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