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M. Sc. Thesis

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Geophysical surveys and dredging in Davis Strait have shown that the Tertiary volcanics of the West Greenland basin continue offshore for many tens of kilometres. The offshore sequence is similar in structure to the terrestrial volcanics, and is composed of shallow westward dipping basalt flows which underlie, on the west, younger sediments and abut against Precambrian gneisses on the south and east. The eastern margin is fault bounded, a seaward continuation of the faulted margin of Cretaceous-Tertiary sediments on land. Several magnetic profiles have established a northern boundary of the offshore province 100 km north of the northernmost occurrence of volcanics on land.

Geochemical analyses and petrographical examinations of the dredge samples have confirmed that the offshore series is composed of subaerial feldspar-phyric basalts similar to the feldspar-phyric volcanics in the West Greenland basin. Opaque petrography and magnetic property examinations show that the volcanics have Q ratios ranging from 2 to 20 and an opaque mineralogy similar to many previously described volcanics.

The bathymetry of the West Greenland shelf was examined with respect to the 鈥渕arginal channel鈥� problem. The prominent north-south trending channels southwest of Egedesminde and north of Upernavik may delineate the offshore extension of the eastern faulted margin of the West Greenland basin. However, their tectonic origin and their continuity with the more typical marginal channels in Melville bay and to the south near Godthaab are evidence in favor of an initial structural origin of marginal channels on the West Greenland shelf.

An area of weak magnetic characteristics, northwest of Nugssuaq peninsula may show an offshore continuation and substantial thickening of the sediments of the West Greenland basin. The presence of hydrocarbons and potential source rocks on Nugssuaq peninsula, the absence of basalts overlying these offshore sediments and the thickened sequence make the area attractive for petroleum exploration.

Finally, the results of this survey are added to previous geological and geophysical studies in the Baffin Bay-Labrador Sea regions to formulate a model for the geological development of Baffin Bay and Davis Strait.

Initial structural weaknesses were developed in the Late Precambrian by rifting without seafloor spreading. This Hadrynian rifting formed northwest trending grabens on Baffin Island, and in proto-Baffin Bay. The area appears to have been a stable cratonic block for 500 my. Sediments may have been continuously deposited in Baffin Bay in the interval between the Lower Palaeozoic and the Jurassic. Limnic and fluviatile sediments were deposited in the West Greenland area in the mid-Cretaceous. Marine trangressions affected the area in the Late Cretaceous-early Tertiary. Volcanic activity began in the early Tertiary in the Davis Strait area and halted further marine sedimentation. The initial extrusives were subaqueous breccias and subaerial olivine basalts and were deposited on either side of the Baffin Bay graben. Later the continental crust was severed in this graben and the volcanic activity in the form of feldspar-phyric basalts greatly extended the West Greenland province. This activity was entirely confined to the west of the Baffin Bay graben. The separation of Greenland and Canada probably ceased at about 47 my, while the extrusive volcanism declined and stopped. Younger sediments have since been deposited on the West Greenland shelf of the west of the offshore volcanic sequence and in Baffin Bay.

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Pages:238
Supervisor: M. J. Keen