Multiple post-Svecofennian 1750-1560 Ma pegmatite dykes in Archaean-Palaeoproterozoic rocks of the West Troms Basement Complex, North Norway: Geological significance and regional implications

The West Troms Basement Complex, North Norway, consist of Meosarchaean, Neoarchaean and Palaeoproterozoic crust which likely represent the continuation of the Karelian craton of the Fennoscandian Shield beneath and across the Caledonian nappes. The complex is transected by several meta-sedimentary/volcanic belts with ages from ca. 2.7 to 1.9 Ga, and linear ductile shear zones that record polyphase deformation after emplacement of several late-Svecofennian plutonic complexes (1.80-1.79 Ga). The Astridal supracrustal belt of the Senja shear zone was intruded by various generations of granite pegmatite dykes, which yield zircon and titanite U-Pb ages ranging between 1758 and 1562 Ma, with evidence of a weak Caledonian overprint at about 400 Ma that formed or reset some, but not all, titanites. The age range indicates that formation of the pegmatites occurred after termination of the main Svecofennian orogeny (1.92-1.79 Ga) of the Karelian craton. Comparison within the larger scale context of the Fennoscandian Shield suggests that emplacement of these pegmatites may have been caused by late-stage reactivation of intracratonic shear zones, possibly reflecting distal effects of deeper magmatic processes such as intrusion of coeval aged rapakivi granite suites (ca. 1.65-1.5 Ga) in Finland, and/or the Mesoproterozoic Gothian orogeny and magmatism affecting the southwestern parts of Fennoscandia. The Mesoproterozoic ages, however, also correspond to late Laxfordian (ca. 1.7-1.6 Ga) tectonic events in the Lewisian basement on the Laurentian margin of Scotland, suggesting a potential early link between these basement complexes. (C) 2015 Elsevier B.V. All rights reserved.