U–Pb geochronology of two discrete Ordovician high-pressure metamorphic events in the Seve Nappe Complex, Scandinavian Caledonides

摘要: U–Pb geochronology for eclogites in two different areas of the Seve Nappe Complex (SNC) Sweden confirms previous indications discrete Ordovician high-pressure events affecting various parts complex. In Norrbotten, just north Arctic circle, from Tsakkok and Vaimok Lenses yield identical metamorphic zircon ages 482 ± 1 Ma. Titanite a metagabbro Lens retains an older age 607 2 Ma, which may date protolith coeval with mafic dikes overlying Sarek Lens; high-U cores one also indicate similar age. Farther south, Jamtland, Tjeliken eclogite yields significantly younger 446 Although they support discrepancy between Norrbotten Jamtland eclogites, both suites are ca. 20 m.y. than previously reported Sm–Nd ages. The latter either represent early prograde growth or be spuriously too old due to isotopic disequilibrium. SNC has traditionally been taken outermost margin Baltica, linking Early Caledonian eclogite–forming subduction Baltica below offshore arc. Alternatively, coincidence these eclogite-forming orogenic phases recorded on Laurentian point origin other regions Iapetus Ocean.