Abstract
The Nagssugtoqidian mobile belt is a 240 km wide zone of deformation and plutonic activity which cuts across the Archaean craton of East Greenland. The belt was established 2600 m.y. ago by the formation of vertical E-W shear zones and the syntectonic intrusion of basic dykes. Tectonic activity along the E-W shear zones was followed by the emplacement of tonalitic intrusions, the Blokken gneisses, 2350 m.y. ago in the central parts of the mobile belt. The emplacement of the Blokken gneisses was accompanied and followed by further emplacement of basic dykes. These are synplutonic in the centre of the mobile belt but are emplaced into more rigid crust in the marginal areas of the belt and in the Archaean craton to the north and south. During a second major tectonic and thermal episode circa 1900 m.y. ago, the region was deformed by thrusting from the north. In the southem part of the mobile belt the earlier steep shear zones are cut by shear zones dipping gently northwards in which rocks are downgraded to greenschist facies. The grade of metamorphism increases northwards and shear zones are replaced by open folds with axial surfaces which dip gently northwards. The increasing ductility in the centre of and northem part of the belt is associated with the intrusion of charnockitic plutons and their granulite facies aureoles. Regional uplift occurred before the intrusion of high level post-tectonic plutons of diorite and granite 1550 m.y. ago.
Highlights
The Nagssugtoqidian mobile belt of East Greenland forms a well defined struCtural province centred about Angmagssalik and extending for 240 km across strike (Bridgwater, 1976, Bridgwater et al, 1977, 1978)
We estimate that at least 90 per cent of the rocks within the mobile belt are Archaean gneisses and supracrustal rocks which have been affected by later tectonic and metamorphic processes; the remaining 10 per cent consisting of relatively restricted amounts of Proterozoic basic dykes and syn- to post tectonic intrusions
Compared to the Archaean gneiss complexes to the north and south the Nagssugtoqidian mobile belt contains a relatively high proportion of Archaean supracrustal rocks dominated by pelitic and semipelitic sediments with minor quartzites, calcareous units, thin ironstones, and amphibolites. This is comparable to the increase in supracrustal rocks seen in the Nagssugtoqidian of West Greenland
Summary
The Nagssugtoqidian mobile belt of East Greenland forms a well defined struCtural province centred about Angmagssalik (fig. 1) and extending for 240 km across strike (Bridgwater, 1976, Bridgwater et al, 1977, 1978). Compared to the Archaean gneiss complexes to the north and south the Nagssugtoqidian mobile belt contains a relatively high proportion of Archaean supracrustal rocks dominated by pelitic and semipelitic sediments with minor quartzites, calcareous units, thin ironstones, and amphibolites. This is comparable to the increase in supracrustal rocks seen in the Nagssugtoqidian of West Greenland. The main northern boundary of the Nagssugtoqidian at the mouth of Kangerdlugssuatsiaq is well defined by an E-W steeply dipping belt af high deformation North of this boundary the Archaean basement rocks are little affected by Nagssugtoqidian movements except for local well-defined narrow shear belts and fractures. Both U and Pb were added to the gneisses during retrogression and it is hoped to obtain a more precise age of metasomatism in the shear zones using U-Pb determination on zircons
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
