New interpretations on palaeomagnetic data from the Nagssugtoqidian mobile belt in Greenland

摘要

The principles governing directions of magnetisation in a metamorphic terrain, which has experienced slow cooling during uplift, are reiterated. These principles are illustrated in areas affected by the Nagssugtoqidian metamorphism in West and East Greenland. Directions of magnetisation in the Kangamiut dykes in the Nagssugtoqidian block and in the craton to the south are similar to each other. The directions in the dykes are close to those in the surrounding gneisses, implying magnetisation within a relatively short time. Their palaeomagnetic poles are close to those from Nagssugtoqidian localities elsewhere in West and East Greenland.Between-site and within-site directions in the dykes are asymmetrical, which is attributed to Apparent Polar Wandering. A statistical method of plotting Apparent Polar Wander Paths is presented. Such paths from dykes in the Archaean and Nagssugtoqidian regions are similar, from which a Composite path is drawn, thus establishing that the Apparent Polar Wander Path for Greenland lies between 0°N, 310°E, and 22°N, 260°E, in the Palaeoproterozoic at about 1750. Ma, upon cooling after the Nagssugtoqidian metamorphism. Similar Apparent Polar Wander Paths have been drawn from other localities in West Greenland. Numerous Poles from East and West Greenland fall close to this path, and are thus of Nagssugtoqidian age. The mean Nagssugtoqidian pole from eight representative studies lies at 20.3°N, 278.3°E (dp/dm = 4.8°/6.4°).