Mafic dyke swarms of the Baltica-Iapetus transition, Seve Nappe Complex of the Sarek Mts., Swedish Caledonides

Abstract Mafic dyke swarms of the Baltica-Iapetus transition, Seve Nappe Complex of the Sarek Mts., Swedish Caledonides With respect to petrography and chemistry, the Sarek dolerites compare excellently to T-MORB as far as REE abundance patterns and some trace element ratios are concerned: chondrite normalized (La/Sm) = 0.77–1.04 and (La/Yb) = 1.2–2.9; Zr/Nb = 8.3–11.6; Zr/Y = 2.8–4.8; Y/Nb = 1.9–4.3. However, high abundances of LIL elements and straddling of boundaries to fields of destructive margins in Nb-Y-Zr and Hf-Ta-Th discrimination diagrams indicate a mixed magmatectonic signature. In this respect, the Sarek dolerites compare to basalts of ensialic back-arc basins e.g. the Gulf of California. However, such a setting is incompatible with our present knowledge about the Baltoscandian scenario 500–600 Ma ago, unless the Sarek sheeted dyke complex was part of the Laurentian passive margin. The favoured interpretation is a situation similar to the present-day opening of the South Atlantic Ocean, where...