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

• Main Authors: John A. Korstgård, Bo Møller Stensgaard, Thorkild M. Rasmussen
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: aeromagnetic data; magnetic anomalies; metamorphic facies; Nagssugtoqidian orogen; West Greenland; Greenland; Itilleq
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.547.2241; http://www.geus.dk/publications/bull/nr11/nr11_p179-184.pdf

Within the southern Nagssugtoqidian orogen in West Greenland metamorphic terrains of both Ar-chaean 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 fab-rics 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. Me-tamorphism and deformation north of Itilleq involve both dykes and host gneisses, and the metamor-phic grade is amphibolite facies increasing to granulite facies at the northern boundary of the south-ern 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.