Magnetic anomalies and metamorphic boundaries in the southern Nagssugtoqidian orogen, West Greenland

Authors

  • John A. Korstgård Department of Earth Sciences, University of Aarhus, Høegh-Guldbergsgade 2, DK-8000 Århus C, Denmark
  • Bo Møller Stensgaard Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
  • Thorkild M. Rasmussen Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark

DOI:

https://doi.org/10.34194/geusb.v11.4930

Keywords:

aeromagnetic data, magnetic anomalies, metamorphic facies, Nagssugtoqidian orogen, West Greenland

Abstract

Within the southern Nagssugtoqidian orogen in West Greenland metamorphic terrains of both Archaean and Palaeoproterozoic ages occur with metamorphic grade varying from low amphibolite facies to granulite facies. The determination of the relative ages of the different metamorphic terrains is greatly aided by the intrusion of the 2 Ga Kangâmiut dyke swarm along a NNE trend. In Archaean areas dykes cross-cut gneiss structures, and the host gneisses are in amphibolite to granulite facies. Along Itilleq strong shearing in an E–W-oriented zone caused retrogression of surrounding gneisses to low amphibolite facies. Within this Itivdleq shear zone Kangâmiut dykes follow the E–W shear fabrics giving the impression that dykes were reoriented by the shearing. However, the dykes remain largely undeformed and unmetamorphosed, indicating that the shear zone was established prior to dyke emplacement and that the orientation of the dykes here was governed by the shear fabric. Metamorphism and deformation north of Itilleq involve both dykes and host gneisses, and the metamorphic grade is amphibolite facies increasing to granulite facies at the northern boundary of the southern Nagssugtoqidian orogen. Here a zone of strong deformation, the Ikertôq thrust zone, coincides roughly with the amphibolite–granulite facies transition. Total magnetic field intensity anomalies from aeromagnetic data coincide spectacularly with metamorphic boundaries and reflect changes in content of the magnetic minerals at facies transitions. Even the nature of facies transitions is apparent. Static metamorphic boundaries are gradual whereas dynamic boundaries along deformation zones are abrupt.

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Published

2006-12-05

How to Cite

Korstgård, J. A. ., Møller Stensgaard, B. ., & Rasmussen, T. M. . (2006). Magnetic anomalies and metamorphic boundaries in the southern Nagssugtoqidian orogen, West Greenland. GEUS Bulletin, 11, 179–184. https://doi.org/10.34194/geusb.v11.4930

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