The anorogenic Noran intrusion ‐ a Mesoproterozoic rapakivi massif in south‐central Sweden

Abstract

The Noran alkali granites and quartz syenites form an anorogenic, c. 1×1.5 km intrusion within the Palaeoproterozoic late‐orogenic Svecokarelian Malingsbo granite in western Bergslagen, south‐central Sweden. The intrusion postdates all significant, identified tectonic movements in the region, but is itself intruded by several dykes which may be related to the granite itself. To the south, it is bordered by a prominent 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 amphi‐bole and quartz. Geochemically, it is an A‐type, within‐plate intrusion with geochemical characteristics similar to other Fennoscandian rapakivi granites. The Sr contents are very low, Rb/Sr ratios high, and the Sr isotope 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 dated 1.65 to 1.50 Ga old Fennoscandian rapakivi granites, and fits to and extends the previously recognized westward trend of younging emplacement ages.

Claesson, S. & Kresten, P., 1997: The anorogenic Noran intrusion ‐ a Mesoproterozoic rapakivi massif in south‐central Sweden. GFF, Vol. 119 (Pt. 2, June), pp. 115–122. Stockholm. ISSN 1103–5897.

Keywords:

• Noran
• alkali granite
• alkali quartz syenite
• rapakivi
• Rb‐Sr
• U‐Pb
• zircon age
• geochemistry
• Bergslagen
• Sweden