Passive margins of the North and Central Atlantic: A comparative study

The main features of the volcanic and nonvolcanic passive margins of the North and Central Atlantic are considered. The margins are compared using rather well-studied reference tectonotypes as examples. The conjugate margins of the Norwegian-Greenland region and the margins of West Iberia and Newfoundland are chosen as tectonotypes of volcanic and nonvolcanic margins, respectively. The structural and magmatic features of the margins and their preceding history are discussed. A complex of interrelated attributes is shown for each tectonotype. The Norwegian-Greenland region close to the Iceland plume is distinguished by narrow zones of stretched continental crust, rapid localization of stretching with breakup of the continent, a high rate of subsequent spreading, and intense magmatism with the formation of a thick new crust at the margin and the adjacent oceanic zone. The Iberia-Newfoundland region, remote from the plumes, is characterized by wide zones of stretched continental crust, long-term and diachronous prebreakup extension propagating northward, extremely restricted mantle melting during rifting and initial spreading, and frequent occurrence of ancient crustal complexes and serpentinized mantle rocks at the margin. Crustal faults and a thin tectonized oceanic crust appear along the margin under conditions of slow spreading. A model of hot and fast spreading with a high degree of melting in the mantle is applicable to the Norwegian-Greenland region, whereas a model of cold and slow amagmatic rifting with a long pre-breakup stretching and thinning of the lithosphere is appropriate to the Iberia-Newfoundland margins. The differences in the development of the margins is determined by the interaction of many factors: deep temperature, rheology of the underlying lithosphere, heterogeneities in the previously formed crust, and the duration and rate of stretching. All of these factors can be related to the effect of deep plumes and propagation of the extension zone toward the segments of the cold Atlantic lithosphere. Both types of margins also reveal similar features, in particular asymmetry. It is suggested that the rotation forces superimposed on the general tectonomagmatic pattern controlled by plumes could have been the cause of structural asymmetry.