We present new structural, geochemical and U–Pb zircon data from syn- to late-orogenic sedimentary–volcanic basins in the southwestern part of the Trondheim Nappe Complex, central Norwegian Caledonides. In this area, a succession of enriched mid-ocean ridge basalt type metabasalt, jasper, ribbon chert with associated sandstone and conglomerate, and green siltstone is interpreted to represent volcanism and sedimentation in a hitherto little-known spreading-dominated tectonic environment. This environment is different from the suprasubduction-zone ophiolite setting dominating the Iapetus rock record elsewhere in the Scandinavian Caledonides. This volcanic and sedimentary succession was overturned and isoclinally folded in a pre-427 Ma orogenic phase. Post-427 Ma cross-bedded sandstones were deposited on the eroded surface of the previously deformed rocks, representing a rare example of a late Silurian or younger sedimentary basin within the Scandinavian Caledonides. The cross-bedded sandstones are intercalated with and/or overlain by post-427 Ma intermediate volcanic or subvolcanic rocks of calc-alkaline composition, representing a hitherto unknown volcanic phase within the Trondheim Nappe Complex and elsewhere within the Scandinavian Caledonides. Their particular geochemical signature could be the result of late-stage subduction-zone volcanism just prior to the onset of continent–continent collision between Baltica and Laurentia, or much younger post-collisional extensional melting with inherited subduction signatures.

Supplementary material: A description of analytical methods and a table of geochronological data from LA-ICP-MS analysis of zircons are available at https://doi.org/10.6084/m9.figshare.c.3994605.

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