Pre-Quaternary geology of Southwest Greenland and its bearing on North Atlantic correlation problems

Two major divisions of Precambrian plutonic rocks are present in West Greenland south of 62°30′ N lat. The oldest (pre-Ketilidian) rocks, giving ages between 2,500 and 2,700 m.y., are in the north. They consist mainly of gneisses, but include amphibolite and mica-schist and contain a belt of locally migmatized supracrustal rocks (the Tartoq Group). The gneisses and the supracrustal rocks are cut by several generations of cratogenic basic dikes.The pre-Ketilidian rocks are overlain unconformably by Ketilidian metasedimentary and metavolcanic rocks at approximately 61°15′ N lat. Southward the Ketilidian supracrustal rocks and the underlying gneisses and basic dikes are affected progressively by increasing deformation and plutonism in the Ketilidian mobile belt.In the Ketilidian mobile belt, which extends from approximately 61° 15′ N lat. to the southern tip of Greenland, two plutonic episodes are recognized: (1) the main Ketilidian plutonic episode (?1,800 m.y.), in which the main tectonic trends and metamorphic features of the mobile belt were established and large masses of granite were introduced, and (2) the Sanerutian plutonic episode, marked by renewed movement on older structures, reactivation of older granites, and emplacement of a suite of norite, diorite, and granite dated between 1,500 and 1,640 m.y.The subsequent cratogenic Gardar period was marked by major faulting, deposition of continental sand and associated volcanic rocks, and, during the period from 1,0 to 1,300 m.y. ago, by alkalic magmatism.The only post-Gardar–pre-Quaternary event recognized is the intrusion of a coast-parallel swarm of middle to late Phanerozoic basic dikes.Correlation possibilities between southwest Greenland and Labrador are suggested. Correlations between Greenland and Scotland of other than a general nature are regarded as less well founded.