THE ANOROGENIC NORAN INTRUSION - A MESOPROTEROZOIC RAPAKIVI MASSIF INSOUTH-CENTRAL SWEDEN

The Noran alkali granites and quartz syenites form an anorogenic, c. 1 x1.5 km intrusion within the Palaeoproterozoic late-orogenic Svecokare lian Malingsbo granite in western Bergslagen, south-central Sweden. Th e intrusion postdates all significant, identified tectonic movements i n the region, but is itself intruded by several dykes which may be rel ated to the granite itself. To the south, it is bordered by a prominen t brittle shear zone, which may have provided a pathway for the magma. The Noran granite/quartz syenite is typically a pink, medium-grained peralkaline, ''dry'', hypersolvus rock with interstitial amphibole and quartz. Geochemically, it is an A-type, within-plate intrusion with g eochemical characteristics similar to other Fennoscandian rapakivi gra nites. The Sr contents are very low, Rh/Sr ratios high, and the Sr iso tope system in the rock is disturbed. The zircon U-Pb age is 1469+/-10 Ma. The Noran pluton is thus slightly younger than the previously dat ed 1.65 to 1.50 Ga old Fennoscandian rapakivi granites, and fits to an d extends the previously recognized westward trend of younging emplace ment ages.