Timing and tectonic significance of Sveconorwegian A-type granitic magmatism in Telemark, southern Norway: New results from laser-ablation ICPMS U-Pb dating of zircon
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The ages of six Sveconorwegian A-type granites without penetrative deformational fabric and an intrusive rhyolite porphyry from Telemark, southern Norway, have been determined by laser ablation inductively coupled plasmasource mass spectrometry (LAM-ICPMS) on magmatic zircons. The emplacement ages span ca.250 Ma: Åmannsbu (rhyolite porphyry) at 1168 \u00B127 Ma, Fjellstadfjell at 1151 \u00B19 Ma, Venås at 1157 \u00B17 Ma, Otternes at 1023 \u00B124 Ma, Torsdalsfjell at 990 \u00B114 Ma, Vehuskjerringa at 932 \u00B14 Ma and Tørdal at 918 \u00B17 Ma. Inherited zircons in the granites include xenocrysts derived from Sveconorwegian rocks, ca.1500 Ma Rjukan Group metarhyolite and \/ or slightly younger intrusive rocks, and rare but significant zircons derived from Paleoproterozoic protosources corresponding in age to intrusions of the Transscandinavian Igneous Belt. The zircon U-Pb ages obtained in this study confirm the early start and long duration of A-type granitic magmatism in Telemark, suggesting that this magmatism must be related to several tectonic events, and support the existence of Paleoproterozoic rocks at depth in southern Norway.