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Original Article |
1 145, Stanway Road, Risinghurst, Headington, Oxford OX3 8HU, UK (e-mail: crlfriend@yahoo.co.uk)
2 2Research School of Earth Sciences, Australian National University, Canberra, A.C.T. 0200, Australia
In the south of the Nuuk region of West Greenland our 1980s mapping recognized four Archaean gneiss terranes (F
ringehavn, Tre Brødre, Tasiusarsuaq and Akia terranes) with different protolith ages and separate early tectonothermal histories. Later in the Archaean these were juxtaposed and then experienced the same 2700–2500 Ma tectonothermal events. Here we abandon extrapolation of only these four terranes across the whole region, and distinguish two new terranes in the NE. The northernmost Isukasia terrane (previously regarded as the northernmost exposure of the Fringehavn terrane) consists of Palaeoarchaean rocks (>3600 Ma) tectonically bounded on its south by the 3075–2960 Ma Kapisilik terrane; these were juxtaposed and metamorphosed together by 2950 Ma. The previously recognized Fringehavn terrane to the SW is another, separate entity of Palaeoarchaean rocks that was juxtaposed with adjacent terranes only after c. 2800 Ma. Hence in an increasingly complex regional model, there were several mid- to Neoarchaean terrane assembly events, with superimposed ‘orogenies’ from c. 2950 Ma until after 2700 Ma. Although the Fringehavn and Isukasia terranes were incorporated into the later Archaean terrane collage at different times, they might be fragments from a larger Palaeoarchaean complex rifted apart from c. 3500 Ma onwards.
Keywords: West Greenland, Archaean, U–Pb, terranes.
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