Th–U–total Pb monazite geochronology records Ordovician (444 Ma) metamorphism/partial melting and Silurian (419 Ma) thrusting in the Kåfjord Nappe, Norwegian Arctic Caledonides

• Published in: Geologica Carpathica
• Main Authors: Ziemniak, Grzegorz, Kośmińska, Karolina, Petrik, Igor, Janak, Marian, Walczak, Katarzyna, Manecki, Maciej, Majka, Jaroslaw
• Format: Article in Journal/Newspaper
• Language: English
• Published: Uppsala universitet, Mineralogi, petrologi och tektonik 2019
• Subjects: Geology; Geologi; Arctic; Kalak; The ''Y''; Kåfjord; Skibotn
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-401052; https://doi.org/10.2478/geoca-2019-0029

The northern extent of the Scandinavian Caledonides includes the Skibotn Nappe Complex of still debatedstructural position. This paper is focused on part of this complex and presents new U–Th–total Pb monazite dating resultsfor the migmatitic gneiss of the Kåfjord Nappe. The rocks show mineral assemblage of garnet + plagioclase + biotite +white mica + kyanite + rutile ± K-feldspar ± sillimanite. Thermodynamic modelling suggests that garnet was stable at P–Tconditions of ca. 680–720 °C and 8–10 kbars in the stability field of kyanite and the rocks underwent partial meltingduring exhumation following a clockwise P–T path. This episode is dated to 444 ± 12 Ma using chemical Th–U–total Pbdating of the Y-depleted monazite core. Second episode highlighted by growth of secondary white mica resulted fromsubsequent overprint in amphibolite and greenschist facies. Fluid assisted growth of the Y-enriched monazite rim at419 ± 8 Ma marks the timing of the nappe emplacement. Age of migmatization and thrusting in the Kåfjord Nappe issimilar to the Kalak Nappe Complex, and other units of the Middle Allochthon to the south. Nevertheless, the obtainedresults do not allow for unambiguous definition of the tectonostratigraphic position of the Skibotn Nappe Complex.