Ewolucja strukturalna basenu arktyczno-atlantyckiego w kenozoiku

Krzysztof Birkenmajer



The paper gives a sketch of structural evolution of the Arctic-Atlantic Basin during the Cenozoic. The break-up of Laurasia continent close to the Cretaceous/Tertiary boundary proceeded north of Iceland along two major structural lines, the traces of which are now apparently the edges of continental shelves of Greenland and Norway-Svalbard: the Harland Line on the south, and the De Geer Line on the north. In a pre-drift position of the continents, the junction of these systems formed an obtuse angle of 120 degrees, and is still recognisable in sharp turns of continental margins at about 70°N on the eastern, and at 72-73°N on the western sides of the Greenland Sea. The separation of Norway and Greenland north of Iceland along the Harland Line began at about 60-70 Ma, as indicated by the study of magnetic anomalies on the Reykjanes Ridge. The active sea-floor spreading axis - the Aegir Ridge, was located along the line of abyssal hills (seamounts) in central Norwegian Sea and continued northward as buried volcanic ridge on the Vöring Marginal Plateau. About 60 Ma the Lomonosov Ridge began to separate from the northern margin of Eurasian shelf due to the growth of the Gakkel Ridge. During this stage of Early Tertiary extension, a huge pile of plateau basalts (tholeiites) was formed in East Greenland. In Svalbard, the main Tertiary sedimentary basin of Spitsbergen was formed subparallel to the De Gear Line. In the south-west part of the Barents Shelf, the Björnöyrenna-Hammerfest. Basins with probably Tertiary sediment fill, apparently mark a failed arm of a triple junction, the other and active arms being the De Geer and Harland lines. The succeeding stage of Early Tertiary compression (resp. transpression) is well evidenced in Svalbard as strong folding and thrusting of the west coast of Spitsbergen due to dextral translation of the Greenland block respective to the Svalbard-Barents block along the De Geer Line. The fold belt probably continues to the south as far as 71°N along the western margin of the Barents Shelf, as indicated by highly disturbed deeper sediments of the Senja Ridge. The dating of the event is controversial: either Late Paleocene-Eocene or younger. The formation of the Forlandsundet Graben resulting from extension (rift valley), filled with thick Tertiary molasse, succeeded the main folding in Svalbard. The Tromsö Basin (probably superimposed upon the older Hammerfest Basin) seems to be another rift graben of similar age and origin. Both structures are parallel to the De Geer Line. Their age is uncertain: either Paleocene-Eocene or younger. Wrench-faulting subsequent to rifting, transversal to the De Geer Line, has been related to a minor west-east compression. Again the age of the faulting is uncertain. Low values of sea-floor spreading, 0.8 to 0.6 cm/yr north of Iceland, between 40 Ma and 18-20 Ma (Oligocene - Lower Miocene), could reflect stages of Alpine folding in Svalbard or only the latest compression stage of the Spitsbergenian phase. Between 20 and 10 Ma, the spreading rates along the mid-oceanic ridge between Greenland and Europe accelerated. Coast-parallel faulting of Oligocene-Miocene age at Kap Brewster, East Greenland coincides with this extension stage. Late Cenozoic activation of N-S directed faults in Spitsbergen, some of which serving as feeder veins for Late Pleistocene - Early Holocene basaltic volcanoes, could correlate with tension generated at the Knipovitch Ridge.

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