Voluminous occurrences of plateau basalts in both East and West Greenland are not believed to have been continuous across the shield area of central Greenland. Whereas the volcanic rocks are almost exclusively basaltic, intrusive rocks also are present, particularly in East Greenland; these show a wide spectrum of rock types, including granites and nepheline syenites.

Because of the difficulty of access to these areas, knowledge of them is still rather limited, although by compiling information from the literature, tentative conclusions regarding the types of magmas involved and their evolution can be gained. The basalts are mainly tholeiitic, commonly with rather primitive features. Small amounts of both normal alkali basalts and greatly undersaturated basalts are also known. Production of such large quantities of tholeiitic basalt commonly has been correlated with continental breakup in this area. Comparisons of the petrology with other areas in the North Atlantic can be made. The highly alkaline rocks are not represented outside of Greenland, except for the peralkaline granite of Rockall. These present special problems, although late trends towa ds alkaline compositions are well known from other magmatic provinces.

Sedimentary rocks are present in both areas. The stratigraphy in West Greenland is particularly well documented and this, in combination with radiometric ages, shows that magmatic activity was limited almost entirely to the Paleocene. This, as previously noted, is in accordance with the distance of East Greenland from the present mid-ocean ridge and known ocean-floor spreading rates. The areas discussed are bounded on the seaward sides by block faults and large-scale crustal warps, a situation which is broadly similar to what is observed in other regions of crustal extension.

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