Passive margins of the North and Central Atlantic: A comparative study |
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Authors: | E N Melankholina |
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Institution: | 1.Geological Institute,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | 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. |
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