NJG83-3-05
2003
Geochronology and petrology of the Tielma Magmatic Complex, northern Swedish Caledonides – results and tectonic implications
83
3
pp. 243-257
82-92394-09-5

In the Caledonides of Scandinavia a lower part of the nappe pile, the Middle Allochthon, consists of metasedimentary rocks and orthogneisses, transported in a southeastern direction and presumably derived from the rifted margin of pre-orogenic cratonic Baltica. In the Sarek-Kvikkjokk area in northern Sweden, telescoped orthogneisses are composed of lithologies that share characteristics with the autochthonous AMCG (anorthosite-mangerite-charnockite-granite)-suite of the Lofoten Complex in northern Norway. The allochthonous Tielma Magmatic Complex (TMC) consists of syenitic and gabbroic rocks, gabbro dykes and ferrogabbros and contains other noteworthy lithologies, such as anorthosites and Fe-Ti ores, which also occur in the Lofoten Complex. All rock types of this study show strong similarities in their trace element and rare earth element patterns with corresponding lithologies in Lofoten, which could indicate a common source and/or process of formation. U-Pb age determinations on zircons constrain the timing of the magmatic activity in the TMC to between 1776 ± 7 Ma and 1761 ± 9 Ma. Subsequent felsic dykes were dated to 1731 ± 5 Ma. The new geochronological, petrological and structural data from the TMC constrain the geological evolution of these crustal elements, which were probably derived from the outermost cratonic Baltoscandian margin and strengthen a correlation with the Lofoten Complex. This correlation together with structural data on Caledonian transport directions suggest orthogonal transport directions towards ESE during the final phase of nappe emplacement.

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