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North Atlantic Opening |
1 The Geological Survey of Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
2 Geological Museum, Øster Voldgade 5–7, DK-1350 Copenhagen K, Denmark
3 Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
Marine mudstones intercalated with Early Tertiary volcanic hyaloclastites in West Greenland contain dinoflagellate cyst assemblages corresponding to nanoplankton zones NP4-NP8 (Danian to Thanetian). Sediments correlated with NP3 are known from the bottom of the volcanic sequence, whereas the top of the sequence is non-marine. A horizon with normally-magnetized subaerial lavas correlates with hyaloclastites within the NP4 interval. This horizon must correspond to magnetic polarity zone 27N; the overlying reversely-magnetized lavas are assumed to belong to both polarity zones 26R and 25R. The main plateau-building volcanic phase in West Greenland is thereby constrained between ‘top polarity chron C28N’ and ‘top polarity chron C25R’, a time interval of 5–6 Ma.
In comparison with other parts of the North Atlantic Tertiary Igneous Province, the volcanism in West Greenland started at an early stage, and the main plateau-building phase was finished before the volcanism in East Greenland started in the NP9 interval (C24R). Sea-floor formation and onshore picrite volcanism started almost simultaneously within a region; first along the West Greenland margin and later along the East Greenland margin. In terms of an impinging mantle plume in the North Atlantic, the volcanism started over the peripheral parts and not over the central part. The differences in timing and character of the volcanic products in the North Atlantic indicate a considerable lithospheric control. The early, picrite-dominated volcanism in West Greenland may be caused by channelling of hot material from the axial part of the plume, impinging on a thick Archaean lithosphere beneath central to eastern Greenland, towards the west into a pre-existing lithospheric ‘thinspot’. The switch of the onshore volcanism from West to East Greenland may be caused by a concomitant switch of the hot axial plume flow from west to east because of the westwards drift of the plate over the plume.
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