LINKING ONSHORE AND OFFSHORE GEOLOGY IN GREENLAND
Igneous rocks in the Davis Strait

Lotte Melchior Larsen, in collaboration with GEUS' Department of Stratigraphy and Marie-Claude Williamson (Geol. Surv. Canada).

Igneous rocks were deposited during several episodes in the sedimentary basins offshore West Greenland and are studied in order to improve the understanding of the basin development, which is important for hydrocarbon exploration in the area and promotion of the region towards the international petroleum industry. The rocks occur as lava flows, sills, and possible intrusions and central volcanoes. They have been sampled in wells and dredges and geochemically fingerprinted with modern ICP-MS trace element analyses. A few suitable samples have been dated.
A related project is the investigation of onshore Mesozoic–Tertiary dyke swarms, see.

Old basalt samples from the wells Hellefisk-1 and Nukik-2 have been re-analysed, and the results show that the rocks are geochemically depleted but deviate from normal ocean-floor basalts by having higher contents of large-ion-lithophile elements.

Basalt pebbles have been dredged from the Davis Strait and Labrador Sea in 2003. Most of these appear to be of local derivation, though some are ice-rafted. Result highlights:
Samples from the Davis Strait High are geochemically depleted, more so than the neighbouring onshore volcanics on Baffin Island and Disko, though the age is the same, Paleocene around 60 Ma. Three samples are crustally contaminated, confirming the presence of continental crust in the Davis Strait High.
Samples from the wall of a large submarine canyon are enriched tholeiitic basalts of non-oceanic character, dissimilar to most known onshore basalts in either West or East Greenland. The age is Paleocene-Eocene, about 55 Ma. Samples from a volcano-like structure in the Labrador Sea, known from seismic profiles, are highly enriched alkali basalts, unlikely to be generated in areas with oceanic crust and mantle. Other samples from the same structure are enriched tholeiitic basalts similar to those from the canyon wall, but the age is Eocene, about 50 Ma.
The gneiss basement was dredged from the canyon wall; zircons from a gneiss sample yielded a 207Pb/206Pb age of c 2740 Ma, confirming the general assumption that the Archaean North Atlantic craton extends well into the sea-covered shelf areas.
Dredging has continued in 2004, and the new samples will be analysed in 2004-2005. The work is financed by the Bureau of Minerals and Petroleum in Nuuk.

References
Williamson, M-C., Villeneuve, M. E., Larsen, L. M., Jackson, H. R., Oakey, G. N., and MacLean, B. 2001. Age and petrology of offshore basalts from the Southeast Baffin Island Shelf, Davis Strait, and the western Greenland continental margin. Geological Association of Canada / Mineralogical Association of Canada Joint Annual Meeting, St. John's, Newfoundland, Canada, May 27–30, 2001. Abstracts Volume 26, p. 162.

Williamson, M-C., Larsen, L.M., Jackson, H.R.& Oakey, G.N. 2003. Evolution of the Baffin Island–West Greenland Tertiary Volcanic Province: Evidence from basaltic rocks on the conjugate margins. EGS–AGU–EUG Joint Assembly, Nice, France, April 2003. Geophysical Research Abstracts 5, abstract no. 06113. CD-ROM only.