NJG95-3/4-08
2015
Geochronology of the Palaeoproterozoic Kautokeino Greenstone Belt, Finnmark, Norway: Tectonic implications in a Fennoscandia context
95
3, 4
365-396
978-82-8347-007-9

Zircon U–Pb geochronological data in 18 samples from Finnmarksvidda and one sample from the Repparfjord Tectonic Window, northernNorway, constrain the evolution of the Palaeoproterozoic Kautokeino Greenstone Belt and neighbouring units in a Fennoscandia context. The Jergul Complex is an Archaean cratonic block of Karelian affinity, made of variably gneissic, tonalite–trondhjemite–granodiorite–granite plutonicrocks formed between 2975 ± 10 and 2776 ± 6 Ma. It is associated with the Archaean Goldenvárri greenstone–schist formation. At the base ofthe Kautokeino Greenstone Belt, the Masi Formation is a typical Jatulian quartzite, hosting a Haaskalehto-type, albite–magnetite-rich, mafic silldated at 2220 ± 7 Ma. The Lik?á and ?áskejas formations represent the main event of basaltic magmatism. A synvolcanic metagabbro dates thismagmatism at 2137 ± 5 Ma. The geochemical and Nd isotopic signature of the ?áskejas Formation (eNd = +2.2 ± 1.7) is remarkably similar to coeval dykes intruding the Archaean Karelian Craton in Finland and Russia (eNd = +2.5 ± 1.0). The ?áskejas Formation can be correlated with the Kvenvik Formation in the Alta–Kvænangen Tectonic Window. Two large granite plutons yield ages of 1888 ± 7 and 1865 ± 8 Ma, and provide a maximum age for shearing along two prominent NNW–SSE-oriented shear zones recording Svecokarelian transpression. The Bidjovagge Au–Cu deposit formed around 1886 to 1837 Ma and is also related to this NNW–SSE-oriented shear system. The Ráiseatnu Complex is mainly composed of granitic gneisses formed between 1868 ± 13 and 1828 ± 5 Ma, and containing metasediment rafts and zircon xenocrysts ranging from c. 3100 to 2437 Ma.The Kautokeino Greenstone Belt and Ráiseatnu Complex are interpreted as Palaeoproterozoic, pericontinental, lithospheric domains formed during rifting between Archaean cratonic domains. They accommodated oblique convergence between the Karelian and the Norrbotten Archaean cratonsduring the Svecokarelian orogeny.

Print