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Grønlands Geologiske Undersøgelse, Øster Voldgade 10, 1350 Copenhagen K, Denmark
The Tertiary alkaline magmatism in E Greenland is the result of the processes related to the continental break-up of the N Atlantic in the Lower Tertiary. The alkaline rocks are divided into three groups: A, inland alkaline lavas, dykes and intrusive complexes of nephelinitic parentage; B, mildly-alkaline to nephelinitic mafic lavas and dykes mostly in areas that previously experienced tholeiitic magmatism; C, salic subalkaline to alkaline dykes and intrusive complexes related to group B.
All three groups are exposed over about 1000 km along the E coast of Greenland, and close to 100 intrusions have been identified, excluding the very intense dyke-swarms. The rocks of nephelinitic parentage occur inland about 100 km W of the coastal zone of most intense magmatism and are believed to constitute an alkaline ‘flank’ activity to the tholeiitic magmatism of the spreading ridge. Early tholeiites and the nephelinites are thought to be derived from the same mantle source. Both group B and group C rocks occur along the coast and along what has been called the ‘initial magmatic lineament’, which in some areas evolved to a spreading zone of intense tholeiitic magmatism. The group B rocks may have been generated in the tholeiite feeder system after the end of the tholeiitic magmatism by processes in replenished magma chambers. Interaction between the magmas in the feeder system and the Archaean crust generated the subalkaline to alkaline salic liquids of group C. The occurrences of the alkaline rocks and their relationships with one another, with the preceding tholeiitic magmatism and with the process of continental break-up are described, and petrogenetic models are presented.
