The Leirungsmyran gabbroic complex, in the northeastern part of the Jotun Nappe, yields a zircon (and titanite ) U-Pb age of 1450 ± 3 Ma, indicating an affinity of this intrusion with anorogenic plutons in the Baltoscandian and Laurentian Shields. The Leirungsmyran gabbroic complex Jacks the structural and metamorphic features typical of granulite to amphibolite facies ultramafic to felsic rocks elsewhere in the nappe. Similarly, the U-Pb isotopic systems of zircon and titanite in the Leirungsmyran gabbroic complex were not disturbed during the intense metamorphic and tectonic event at 900 Ma that very strongly affected U-Pb systematics of zircon and titanite in other parts of the nappe. These relationships could reftect a very heterogeneous distribution and intensity of metamorphic and strain features related to a common 900 Ma event. Alternatively, they could be taken to indicate that the Leirungsmyran gabbroic complex is part of a separate thrust-sheet assembled to the other segments of the Jotun Nappe in the late stages of or following the main Sveconorwegian event.

F. Corfu, Department of Geology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ont., Canada, M5S 2C6;
T. F. Emmett, Departmenl of Applied Sciences, Anglia Polytechnic University, East Road, Cambridge, CB1 1PT, UK.