Abstract

Geophysical and bathymetric results have been used for the study of the transitional zone between the Eurasian continent and the Arctic Ocean, which is being considered by the authors as a junction area of continental margins with the adjacent seaward structures, and is dependent of the actual type of the crust found beneath the ocean.The deep Arctic Ocean comprises different types of crust: basins have an oceanic crust with increased sedimentary thickness; the Lomonosov and Mendeleev Ridges have crusts close to subcontinental; and the crust of the Gakkel Ridge is typically mid-oceanic. At least four types of transition zones may be distinguished: (1) 'normal' transition zone, where the 'granitic' layer is wedging out and the crust consists of a thinned sedimentary layer and 'basalt'; this is the junction of the continent and the oceanic basin; (2) a zone where the continental crust thins to the oceanic crust, the 'granitic' layer is absent, and the 'basalt' layer is underlain by the 7.5 km/s layer, rather than the normal mantle; this is represented by the junction of the continent with the rift zone of the median ridge that juts out into the shelf and extends under the continent; (3) a zone where the continental crust thins, the 'granitic' layer is wedging out, but the crust does not thin to the oceanic crust, mainly because of an increase in thickness of sediments; this zone is a junction of the continent with a basin with subcontinental crust; (4) a zone where the continental crust thins, but does not reach oceanic thickness; this is a junction of the continent with the oceanic crust. In the transition zones of the first and third types structural downwarping compensated by the sediments has been developed.The development of the transition zone of the Arctic was intermittent in the geological past, which we see expressed by the asymmetric development of the Greenland–Canadian and Eurasian sectors. These examples of different structures of transition zones are not unique. The transition zone between the Asiatic continent and the Indian Ocean appears to be most similar in its complexity to the transition zone of the Arctic Ocean. However the 'normal' type of transition zone characteristic of much of the continents of Australia, South America, Africa, and parts of other continents frequently occurs here.

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