Abstract

Geophysical and geological surveys conducted in Davis Strait during 1980 together with data collected in the same region in previous years confirm the presence across the Strait of a prominent structural high oriented in a northeast-southwest direction. A large positive free air gravity anomaly is associated with this high. Seismic reflection measurements show the high to be fault-controlled and indicate sediments in excess of two seconds in thickness lie on either side. Strong reflectors that dip parallel to the eastern flank of the high may indicate Paleocene or older basaltic flows interbedded with sediments. Similar reflectors are not observed on the western side. Seismic reflection measurements north and south of the high show the presence of reflectors resembling oceanic-type acoustic basement.

Magnetic anomalies correlatable with seafloor spreading anomalies are not observed in the entire Davis Strait region. Seismic refraction measurments near the Baffin Island shelf break show a 6.8 km/s layer at a depth of 3.5 km underlying sediments of velocity 3.9 km/s. Similar measurments in the central region of the Strait indicate an 18 km thick crust with a velocity of 6.2 km/s overlying mantle with a velocity of 8.5 km/s. Seismic refraction measurements across the high are not definitive enough to ascertain the true nature of the underlying crust. However, the velocity distribution under the high when compared with velocities observed under other oceanic and continental fragments shows similarities to both.

A major portion of this high, particularly the western side, is interpreted to contain a fragment of continental crust which may have formed part of the west Greenland or Baffin Island shelf near the present latitude of Cumberland Sound prior to separation of Greenland from North America. If this is the case, then during late Paleocene or earlier the fragment became detached and subsequently started to move north relative to Baffin Island, either as part of the Greenland plate or independently as a consequence of the translational motion between the North American and Greenland plates. Movement would have stopped in early Oligocene when seafloor spreading ceased in the Labrador Sea and the fragment would have occupied its present position in mid-Davis Strait since that time.