A syn-tectonic metagranite, intruding the structurally uppermost part of the Upper Ordovician/Lower Silurian Balsfjord Group, Lyngen Nappe Complex, on Reinøy, Troms, has been dated by the Rb-Sr method. The obtained isochron age of 432 ± 7 Ma (I.R. 0.71108 ± 0.00025) is interpreted to represent the magmatic crystallization age of the granite, suggesting that deformation and metamorphism of the Balsfjord Group started shortly after deposition. The syn/post-Dl and pre-D2 age for the granite suggests that juxtaposition of the Balsfjord Group and structurally underlying Nordmannvik Nappe and overlying Tromsø Nappe Complex took place during the early Silurian, possibly representing initiation of the Scandian orogenic event in the north Norwegian Caledonides. Such an interpretation is consistent with recently obtained 4fl Ar/39 Ar mineral ages ( amphibole and white mica) from the Balsfjord Group and Nordmann vik Nappe which have yielded cooling ages related to uplift of around 425-420 Ma.
Rb-Sr dating of a syn-tectonic granite within the Lyngen Nappe Complex and its implications for late orogenic evolution of the Troms Caledonides