Palaeomagnetic evidence for the origin of the coastal flexure and dyke swarm in central E Greenland

Abstract

The well known coastal flexure of central E Greenland, with its associated dyke swarm, affects a thick pile of Tertiary basalts and the underlying basement gneisses. It is a major tectonic/magmatic feature of this 9trailing edge9 type continental margin. The original interpretation of Wager & Deer (1938) envisaged the emplacement of the dykes as a fan-shaped swarm in the convex arc of the flexure. Nielsen (1975, 1978) recognized several episodes of dyke emplacement. He interpreted the main swarm (THOL 1) as earlier than the flexure, emplaced vertically into the horizontal basalt pile and subsequently tilted by antithetic faulting during the formation of the flexure. A palaeomagnetic study of the THOL 1 and later dykes shows that the former were emplaced in their present inclined attitude. This discriminates in favour of Wager9s interpretation, while remaining consistent with Nielsen9s view of the post-flexural magmatic history. Modifications to Nielsen9s scheme are suggested to conform with the new evidence, and the implications in relation to the mechanism of flexuring, the timing of tholeiitic magmatism, and the relationship of both to the early spreading history of this sector of the NE Atlantic, are discussed.