Diachronous collision in the Seve Nappe Complex: Evidence from Lu–Hf geochronology of eclogites (Norrbotten, North Sweden)

The collision of Baltica and Laurentia during the Caledonian Orogeny happened at c. 400–420 Ma. However, subduction processes also took place before this main collisional phase tectonic history these is still not fully resolved. Seve Nappe Complex in Sweden has recorded earlier phases. Norrbotten (North Swedish Caledonides) comprises four superimposed nappes emplaced by eastward thrusting (from base to top according conventional structural interpretation): Lower Nappe, Vaimok, Sarek, Tsäkkok Lenses. Eclogites occur Vaimok Lens represents rocks Baltican continental margin intruded Neoproterozoic dolerite dikes which were later eclogitized boudinaged. By contrast, eclogites are former oceanic basalts associated with calcschists, possibly representing ocean–continent transition between Iapetus. Previous age determinations for eclogitization yielded various ages 500 480 Ma, contrast younger (460–450 Ma) ultra high-P metamorphism further south Jämtland. from (one sample) (three samples) lenses dated using Lu–Hf garnet geochronology. Garnet all samples shows prograde zoning major element Lu contents well-defined isochrons following ages: 480.4 ± 1.2 Ma (Vaimok); 487.7 4.6 486.2 3.2, 484.6 (Tsäkkok). interpreted date burial Iapetus–Baltica a west-dipping zone around 485 structurally deeper margin. Previously reported older supported study. difference Jämtland (c. 460–450 488–480 may reflect an island arc irregularly shaped passive or alternatively straight microcontinent (Sarek Lens) accreted upper plate.