Results from a detailed aeromagnetic survey across the northeast Newfoundland margin, Part II: Early opening of the North Atlantic between the British Isles and Newfoundland

Abstract

Poles of rotation for the North Atlantic have been derived from the results of a new aeromagnetic survey northeast of Newfoundland. Reconstruction of the North Atlantic at anomaly 34 time shows a band of large amplitude magnetic anomalies which parallels anomaly 34 on both sides of the Atlantic from Flemish Cap and Goban Spur to the Azores-Gibraltar Fracture Zone. A group of similar anomalies has also been identified in the Bay of Biscay. North of Goban Spur and Flemish Cap, these anomalies follow the ocean-continent boundary. Poles of rotation derived for this anomaly show that it forms an isochron (100–110 m.y.) during the long Cretaceous normal polarity interval. The cause of this anomaly is not definite, but it may represent an increase in the magnetization of the crust during a limited time within the Cretaceous Magnetic Quiet Zone by a process such as replacement of thermoremanent magnetization by chemical remanent magnetization as proposed by Raymond and LaBrecque. The North Atlantic has also been reconstructed at the time of the initial opening in the region between Flemish Cap and the Charlie-Gibbs Fracture Zone, using inferred ocean-continent boundaries on the west and east sides: it has been shown that the entire region could not have saparated at one time, but that spreading between the British Isles and Newfoundland had to progress from south to north. Consequently, when active sea-floor spreading was taking place between Goban Spur and Flemish Cap (about 110 m.y.) the region to the north was still being stretched. The calculated amount of stretching as derived from the reconstructions (about 25%) agrees well with the extension of the lithosphere obtained from modelling the subsidence history of this region, and with the results of deep seismic studies. Active spreading in the north started about 100 m.y. ago.