NJG69-2-02
1989
A seve duplex (Upper Allochthon) at the northern margin of the Grong district (Caledonides of central Norway).
69
2
83-93

Tectonostratigraphic investigations revealed a unit of Seve lithology (Upper Allochthon) beneath the Köli units of the Grong district and above Middle Allochthon units (including the Dearka metapsammites) at the SW margin of the Børgefjell window. The Seve unit is composed of garnet mica schists, gneisses, fine-grained metabasites (the 'Gollomvatnet metabasites', GM), minor quartzites and marbles. According to 16 geochemically analysed samples, the GM are basalts and basaltic andesites and show a clear affinity
to Seve metabasites, both for major and trace elements. The structural evolution is polyphase, with an early, pre-thrusting peak of metamorphism (amphibolite/greenschist grade). Thrusting under lower greenschist grade metamorphic conditions established the present geometry of the Seve unit as a forelanddipping duplex. Subsequent intense folding (NE-SW, E-W, N-S) led to the present map pattern. An OFB/WPB transitional character of the GM may be related to early stages of crustal rifting. Subsequent
collision tectonics led to metamorphism and thrusting of the Seve duplex into its present position.

0029-196X
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