9Evolution of Neoarchaean supracrustal belts at the northern margin of the North Atlantic Craton, West
Archaean craton to the north, to form the Nagssugtoqidian orogen. The Palaeoproterozoic metamor-phic grade and strain intensity decrease northward through the orogen, allowing investigation of the reworked Archaean components in its northern part. Two Archaean supracrustal belts in this region – the...
| Main Authors: | , , , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.494.3932 http://www.geus.dk/publications/bull/nr11/nr11_p009-032.pdf |
| Summary: | Archaean craton to the north, to form the Nagssugtoqidian orogen. The Palaeoproterozoic metamor-phic grade and strain intensity decrease northward through the orogen, allowing investigation of the reworked Archaean components in its northern part. Two Archaean supracrustal belts in this region – the Ikamiut and Kangilinaaq belts – are investigated here using field mapping, aeromagnetic data, zircon geochronology, and geochemistry. Both belts comprise quartzo-feldspathic and pelitic meta-sedimentary rocks, amphibolite, and minor calc-silicate rocks, anorthosite and ultramafic rocks. Pb-Pb and U-Pb dating of detrital zircons and host orthogneisses suggest deposition at c. 2800 Ma (Kan-gilinaaq belt) and after 2740 Ma (Ikamiut belt); both belts have zircons with Neoarchaean metamor-phic rims. Metasedimentary rocks and orthogneisses at Ikamiut share similar steep REE signatures with strong LREE enrichment, consistent with local derivation of the sediment and deposition direct-ly onto or proximal to the regional orthogneiss precursors. Zircon age data from Kangilinaaq indicate both local and distal sources for the sediment there. Geochemical data for Kangilinaaq amphibolites indicate bimodal, mixed felsic–mafic source rocks with island-arc basaltic affinities, consistent with a shelf or arc setting. Both belts experienced a similar tectono-metamorphic history involving Neoar-chaean amphibolite facies peak metamorphism at c. 2740–2700 Ma, possibly due to continued emplace- |
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