Caught between two continents: First identification of the Ediacaran Central Iapetus Magmatic Province in Western Svalbard with palaeogeographic implications during final Rodinia breakup

Abstract

The final fragmentation of Rodinia occurred during the Ediacaran period as the continental blocks of Baltica and Laurentia, as well as Amazonia and West Africa, rifted and drifted apart. It was along this progressively rifted margin that the Iapetus Ocean opened and subsequently closed, creating the Caledonian orogeny (sensu lato), some 100 and 200 million years later. The 0.62–0.54 Ga Central Iapetus Magmatic Province (CIMP), accompanying this break-up, is variously manifested in northern Europe and north-eastern North America as mafic dykes and sills, volcanic rocks, as well as carbonatites. This magmatism is interpreted to be broadly coincident with the so-called Marinoan and Gaskiers glaciations, and the subsequent evolution of metazoans. While the various Precambrian basement blocks of Svalbard are known to carry a Caledonian overprint, the proximity of various parts of Svalbard to either Baltica or Laurentia during final Rodinia breakup in the Ediacaran has yet to be established. Petrographic, geochronological and geochemical data from the variably deformed and metamorphosed coarse-grained mafic units of Oscar II Land (OIIL) from Spitsbergen, Svalbard, are presented here to determine the source of the magma and to elucidate on their palaeogeographic affinity with adjacent crustal blocks/units. An alkali and OIB-like affinity of the mafic units is confirmed by their whole-rock geochemical composition. An ID-TIMS U-Pb baddeleyite crystallisation age determination of 560 ± 12 Ma, obtained from one such mafic unit, contrasts with the published Caledonian (sensu lato) age determinations. These data for OIIL compare well with the broadly coeval and geochemically similar 570–560 Ma Norwegian Seiland Igneous Province, which may have formed a part of Baltica. Temporally and compositionally similar mafic units also occur within the North American Appalachian Belt, as well as the Sept-Îles intrusion, which is part of Laurentia. However, any links between these intrusions with those of Svalbard are yet to be unequivocally demonstrated.