The 616 Ma Old Egersund Basaltic Dike Swarm, Sw Norway, and Late Neoproterozoic Opening of the Iapetus Ocean

Abstract

The Egersund dike swarm of SW Norway is made up of 11 basaltic dikes trending ESE‐WNW. Two groups are defined: porphyritic dikes with bytownite phenocrysts of tholeiitic affinity and aphyric dikes of tholeiitic to alkaline affinity. Baddeleyite in the most alkaline dike gives a U‐Pb intrusive age of 616 ± 3 Ma. The swarm is parallel to the Neoproterozoic southwestern (present‐day orientation) Tornquist margin of Baltica. It is coeval with the Long Range swarm of Labrador which is parallel to the southeastern proto‐Appalachian margin of Laurentia. Both swarms are related to rifting that resulted in the opening of Iapetus ocean. Chronocorrelation of Neoproterozoic rift‐related magmatic suites in western Baltica and eastern Laurentia suggests diachronic opening of Iapetan oceanic basins at ca. 610 Ma along the northwestern Baltoscandian margin of Baltica and at ca. 550 Ma along the proto‐Appalachian margin of Laurentia and Tornquist margin of Baltica.