Comments on 'The palaeomagnetism of the Central Zone of the Lewisian foreland, north-west Scotland' by J. D. A. Piper

• Published in: Geophysical Journal International
• Main Author: Beckmann, George E. J.
• Format: Text
• Language: English
• Published: Oxford University Press 1981
• Subjects: Letter to the editors; Greenland; Angmagssalik; East Greenland
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/66/2/463; https://doi.org/10.1111/j.1365-246X.1981.tb05969.x

Piper suggested that the Lewisian has rotated 30° anticlockwise since magnetization, whereas the opposite appears more likely. The main magnetization in the Lewisian recognized by Piper and Beckmann was imposed upon cooling after the Laxfordian metamorphism at about 1750 (± 50) Ma. The palaeomagnetic pole corresponding to this magnetization is at 37.6° N, 273.2° E ( dp = 3.7°, dm = 5.2°). In Greenland, palaeomagnetic poles similar to each other, with a mean pole at 21.6° N, 280.1° E ( K = 52, A 95 = 9.4°), have been determined from five widely separated regions in central West Greenland and from Angmagssalik in East Greenland. The magnetization observed in all these regions was established upon cooling after the Nagssugtoqidian metamorphism, again at about 1750 (±50) Ma. The Laxfordian and Nagssugtoqidian metamorphisms were equivalent. It is therefore assumed that the two palaeomagnetic poles quoted above were originally identical. Their present difference can be explained by clockwise rotation of north-west Scotland about a local rotation pole since the Lewisian became magnetized, in addition to opening of the Atlantic assuming conventional reconstructions: <l type="ord"> assuming the reconstruction of Bullard, Everett & Smith, the local rotation proposed is 39.5° (± 18.1°) about a pole of rotation at 60.3° N, 354.5° E, or assuming the reconstruction of Le Pichon, Sibuet & Francheteau, the local rotation is 28.0° (±17.7°) about a pole of rotation at 54.1° N, 354.6° E. </l> These proposals of local clockwise rotation of north-west Scotland accord with that of Storetvedt based on palaeomagnetic results from Devonian rocks on the north-west side of the Great Glen Fault.