Publication Details

Nutman, A. P., Bennett, V. C., Friend, C. R. L., Yi, K. & Lee, S. (2015). Mesoarchaean collision of Kapisilik terrane 3070Ma juvenile arc rocks and >3600Ma Isukasia terrane continental crust (Greenland). Precambrian Research, 258 146-160.


The Mesoarchaean Kapisilik and Eoarchaean Isukasia terranes in the Nuuk region of southern West Greenland were tectonically juxtaposed in the Archaean. The north of the Isukasia terrane is distal from the Kapisilik terrane and has only rare growth of ~2690Ma metamorphic zircon and no 2980-2950Ma metamorphic zircon. The southern part of the Isukasia terrane lies between two ~2690Ma shear zones, and has locally preserved high pressure granulite facies assemblages and widespread growth of 2980-2950Ma metamorphic zircon and also sporadic growth of ~2690Ma metamorphic zircon. Within this southern part of the Isukasia terrane there is a folded klippe of mylonitised Mesoarchaean detrital meta-sedimentary rocks (carrying >3600 and ~3070Ma detrital zircons), mafic and ultramafic rocks, with ~2970Ma metamorphic zircon overgrowths. South of the Isukasia terrane is the Kapisilik terrane, containing ~3070Ma arc-related volcanic rocks, gabbro-anorthosites and meta-tonalites, intruded by 2970-2960Ma granites. Zircons of an Ivisârtoq supracrustal belt ~3075Ma intermediate volcanic rock have initial e{open}Hf values of +2 to +5 thus are juvenile crustal additions. ~3070Ma tonalites along the northern edge of the Kapisilik terrane have whole rock positive initial e{open}Nd values and thus are also juvenile crustal additions. In contrast, igneous zircons in 2960Ma granites intruded into juvenile ~3075Ma supracrustal rocks of the Kapisilik terrane have initial e{open}Hf values of -5 to -10, and must have involved the partial melting of >3600Ma Isukasia terrane rocks.The integrated structural and zircon U-Th-Pb-Hf isotopic data show that at 2980-2950. Ma the Kapisilik terrane juvenile arc components collided with, and over-rid, the Isukasia terrane. The southern edge of the Isukasia terrane came to lie in the deep crust under the Ivisârtoq supracrustal belt and melted at 2970-2960. Ma to produce granites. These granites derived from ancient crust rose into the upper crust, where they intruded the overlying allochthonous juvenile ~3075. Ma Ivisârtoq supracrustal belt arc assemblages. The southern edge of the Isukasia terrane is interpreted as an interior nappe of Eoarchaean basement rocks interfolded with a klippe of Mesoarchaean metasedimentary and mafic/ultramafic rocks, both of which are affected by 2980-2950. Ma metamorphism. The mixed Eoarchaean-Mesoarchaean detrital provenance suggests that the klippe could be dismembered components of an accretionary prism or forearc crust. The northern part of the Isukasia terrane is interpreted as foreland, free of 2980-2950. Ma high-grade metamorphic overprint. This shows that the Isukasia terrane is not a coherent block, but contains ancient rocks that are parautochthonous or allochthonous to each other, with contrasting later metamorphic history.At ~2690. Ma the crustal architecture arisen from Mesoarchaean collision between an older continental block and an island arc was reworked along intra-crustal shear zones, coeval with amphibolite facies metamorphism. This reworking followed on from major terrane assembly at 2710-2700. Ma in the southern part of the Nuuk region, when the Eoarchaean Færingehavn terrane was juxtaposed with 2840-2825. Ma arc rocks. Thus the 2980-2950. Ma assembly of the Isukasia and Kapisilik terranes is distinct from the later 2710-2700. Ma terrane assembly further south in the Nuuk region.

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