Exhumation of continental margin rocks from mantle depths to orogenic foreland: example from the Seve Nappe Complex of the central Scandinavian Caledonides

The diamond-bearing Seve Nappe Complex (SNC) in the Scandinavian Caledonides records subduction of continental margin rocks to (ultra)high-pressure conditions at mantle depths, and exhumation thereafter from beneath the hinterland to the Earth’s surface in the foreland. Structural data of the Upper, Middle, and Lower SNC in central Jämtland, Sweden demonstrate a triclinic bulk deformation during the exhumation of the still ductile SNC from crustal levels where migmatites formed. 40 Ar/ 39 Ar data from the Upper SNC constrain the timing of cooling through 450‒300 °C to be ~ 418 to 416 Ma. In combination with a review of the published pressure–temperature–time data and regional geology of the central Scandinavian Caledonides, four stages of exhumation of the central Jämtland SNC are summarized: (1) buoyancy-driven exhumation during ~ 455 to 433 Ma from ultrahigh-pressure depths to granulite-facies depths triggered by tectonic under-pressure; (2) tectonic exhumation in ~ 433 to 418 Ma at lower- to mid-crustal levels resulted from accretion of the Lower Köli Nappes onto Baltica; (3) eduction of the Western Gneiss Region lithosphere and piggyback transport of the SNC in ~ 418 to 375 Ma from hinterland to foreland, coupled with extensional faulting at mid- to upper-crustal levels; and (4) gravitational collapse- and erosion-driven exhumation following the end of the Scandian Orogeny at ~ 375 Ma. This multi-stage exhumation transported the SNC for > 100 km vertically from mantle depths to the Earth’s surface and > 350 km horizontally from the Caledonian hinterland to the foreland. This contribution provides a typical example of the complex exhumation of deeply subducted continental rocks in orogenic belts.