Caledonian terrane analysis in Troms-Tornetrask, northern Scandinavia, utilizing the geochemistry of high-level metabasites

In the Caledonides of the Tometrask-Troms region, northern Scandinavia seve ral thrust sheets occur above structural units representing the shortened, outermost preserved portions of the Late Precambrian-lower Palaeozoic Balto scandian continental margin (Seve Nappes). Most are pelitic in character, w ith sequences of marble and amphibolite occurring at certain levels. On the basis of their position within the regional tectonostratigraphy, they are thought to represent a series of terranes that are suspect and possibly exo tic with respect to Baltoscandia. Major- and trace-element characteristics of amphibolite sheets and lenses from most units above the Seve Nappes disp lay remarkably consistent geochemical signatures. These show clear affiniti es with modem-day basalts from plate-margin settings, notably ocean floor b asalts from a back-are setting. Similarities in lithostratigraphy, tectonom etamorphic evolution and metabasite geochemistry suggest that they represen t an amalgam of exotic oceanic terranes. These were probably derived from t he lower Palaeozoic Iapetus oceanic tract, outboard of their present positi on along the Baltoscandian continental margin. The Smatinden nappe is quite different, containing mafic dykes (now amphibolite) with a pronounced with in-plate basalt geochemistry. This reinforces previously noted differences in lithostratigraphy and tectonothermal evolution, and, on this combined ev idence, this unit is defined as part of a separate, interleaved, suspect te rrane.