U–Pb geochronology along an Archaean geotransect in the West Troms Basement Complex, North Norway
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An Archaean geotransect is well preserved within the West Troms Basement Complex, a basement outlier west of the Caledonides in North Norway, whose structural architecture is the finite result of both Archaean and Palaeoproterozoic (Svecofennian) tectonic events. Geochronology by U–Pb TIMS and SIMS of nine samples of magmatic and migmatitic rocks collected in a transect perpendicular to the NW–SE strike of the complex record three main stages of Archaean magmatism and one superimposed, Neoarchaean, metamorphic high-grade event. The oldest Mesoarchaean ages of 2.92–2.80 Ga are found within a paired tonalitic complex and greenstone belt in the northeast. These rocks are separated by a high-grade, ductile shear zone from younger Neoarchaean rocks with only local, inherited, Mesoarchaean zircons.

The period from 2.75–2.70 Ga was particularly active in the rest of the complex, with intrusion of diorite-granodiorite plutons on Kvaløya and Senja, followed by local migmatisation and another pulse of diorite-granite magmatism between 2.70 and 2.67 Ga. This period was concluded by the intrusion of mafic dykes at 2.671 Ga, documented in one locality on Kvaløya. A latest Neoarchaean age for stromatic migmatite or metamorphism is indicated in two localities by secondary zircon in neosome, with restitic zircon derived from the 2.70–2.67 Ga event. The Archaean rocks were variably reworked, metamorphosed and intruded by felsic and mafic plutons during the Svecofennian (1.8–1.7 Ga) orogeny, and locally also formed the substrate to Palaeoproterozoic supracrustal rocks. Possible correlatives are found in the Lofoten and Vesterålen area to the south and in the Karelian and Norrbotten provinces in the Fennoscandian Shield. Given the tectonostratigraphic position of the West Troms Basement Complex, correlations with Archaean provinces elsewhere in the North Atlantic region are also possible.

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