The continental margin off East and North Greenland
The continental margin off East Greenland between 60o and 76oN can in general terms be described as a volcanic rifted margin. The position of the continent–ocean transition was drawn on the basis of aeromagnetic data supplemented by characteristic features in the NAD reflection seismic data. The absolute seawards (eastern) limit of continental crust cannot overlap areas where linear magnetic anomalies characteristic of oceanic crust can be identified.
The zone off East Greenland shown on the map as underlain by transitional crust [b] was drawn in a rather arbitrary manner, at least with regards to its width. This zone is thought to consist of continental crust with increasing numbers of dykes and other intrusions as oceanic crust is approached.
The continental margin off West Greenland
The continental margin off West Greenland is complex and the interpretation is a subject of discussions. The transition zone between typical oceanic and normal continental crust is certainly much wider off southern West Greenland than it is thought to be anywhere off East and South-East Greenland. The seawards limit of normal continental crust off southern West Greenland lies well to the south-west of the continental slope, at water depths of more than 1500 m. This interpretation of the distribution of crustal types is supported by the structural pattern seen in the seismic lines. Both the normal continental crust and the zone of transitional crust show large tilted fault blocks overlain by syn- and post-rift sediments. The oldest sediments are most likely of Early Cretaceous age.
The crust under Davis Stræde (Davis Strait) is estimated to be 22 km thick, which is intermediate between the thickness of normal oceanic and continental crust.
The crust is therefore interpreted by the Survey as being formed of thinned continental crust, in accordance with the interpretation of the distribution of crustal types farther south. The nature of the crust underlying Baffin Bugt is not obvious. There are no distinct sea-floor spreading magnetic anomalies in this region.
Offshore sedimentary basins
Reflection seismic surveys have shown that large sedimentary basins occur offshore East Greenland between latitudes 67o–72oN and 75o–77oN, and offshore West Greenland between 63o–68oN and 73o–77oN. In the intervening areas off both East and West Greenland there are extensive Lower Tertiary basalts below which there are expected to be thick sedimentary successions, but these cannot be resolved in the seismic data.
North-East Greenland shelf (72°–80°N)
The existence of thick sedimentary successions on the North-East Greenland shelf was first suggested on the basis of interpretation of aeromagnetic data. Judging from the known geology of the Barents Sea, the Norwegian shelf and onshore North-East Greenland, the age of these sediments is likely to be Devonian to Recent, with unconformities in the middle Permian and in the Cretaceous.
On the shelf between latitudes 72o15' and 75o30'N extensive volcanic rocks of presumed Early Tertiary age have been interpreted from the aeromagnetic and seismic data. In the near-shore area these are exposed at the seabed; eastwards they become increasingly deeply buried under younger sediments. It is considered almost certain that the pre-Tertiary sediments interpreted to the north and south of this area continue beneath the volcanic rocks.
Central West Greenland (68°–73°N)
The Lower Tertiary basalts exposed onshore in the Disko – Nuussuaq – Svartenhuk Halvø area continue offshore where they have been mapped from seismic and magnetic data over the entire area between latitudes 68o
and 73oN. In the eastern part of this area the basalts are exposed at the seabed and have been sampled by dredging, but to the west they become increasingly buried under a cover of Eocene and younger sediments. Below the basalts underlaying sediments may be as much as 5 km in thickness.
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