The tertiary dike swarms of the Kangerdlugssuaq area, East Greenland: An example of magmatic development during continental break-up

Detailed field studies supplemented by petrographic and petrochemical data of dikes in the Kangerdlugssuaq area lead to the recognition of six distinct generations, which may be correlated with the major structural and magmatic events in this part of the North Atlantic Province. In order of decreasing age these swarms are:

1. A broad coastparallel dike swarm of high Fe and Ti tholeiitic basalts, identified as feeders for the plateau basalts of East Greenland and intruded prior to coastal flexuring.
2. A radial tholeiitic dike swarm with MORB affinities, related both in chemistry and chronology to the major gabbroic plutons (including Skærgård) and penecontemporaneous with the coastparallel flexure of East Greenland.
3. A coastparallel alkaline dike swarm, most intense some 20 km inland, composed of picritic to hawaiitic rock types and intruded subsequent to flexuring.
4. Peralkaline rhyolites found in the immediate neighbourhood of the nordmarkitic syenites and clearly related to the major period of salic plutonism.
5. A radial strongly alkaline swarm, including several types of alkaline olivine basalts and trachybasalts differentiating to oversaturated trachytes.
6. Simultaneous with the last, a coastparallel dike swarm composed of transitional basalts differentiating to rhyolitic rock types.

In general, all dikes prior to coastal flexuring are tholeiitic basalts and show limited differentiation, those related to the gabbroic plutons show a differentiation, trend similar to that of the lower part of the Skærgård intrusion. After flexuring all dikes belong to more alkaline suites and show considerable degrees of differentiation. The rather complicated evolution spans the period from ca. 58 to ca. 36 MY, i.e. the period of continental break-up in the area.