Palaeomagnetism of the Proterozoic Zig‐Zag Dal Basalt and the Midsommersø Dolerites, eastern North Greenland

Abstract

Summary. Palaeomagnetic investigations are reported from 24 sites in the Proterozoic Zig‐Zag Dal Basalt Formation and 12 sites in the Midsominersø Dolerites of eastern North Greenland. The Zig‐Zag Dal Basalt is a typical tholeiitic flood basalt sequence, and dolerite intrusions in the underlying sandstones are thought to be genetically related to the basalts. After a detailed AF demagnetization programme 19 sites in the basalts and 10 sites in the dolerites reveal one stable component of magnetization, probably of TRM and/or CRM origin residing in small single domain titano‐magnetite grains. The degree of anisotropy has not affected the direction of the remanent magnetization. The maximum axis of the anisotropy ellipsoid is parallel to the flow direction of the magma, whereas the minimum axis is perpendicular to the flow plane. Only one polarity of the geomagnetic field was found. The mean palaeomagnetic pole positions for the two rock types are not significantly different (basalt: 12.2°S, 62.8°E with A95= 3.8°; dolerites: 6.9°S, 62.0°E with A95= 5.1°). After correction for Phanerozoic drift of Greenland the two mean poles compare closely to a relevant North American APW‐curve for 1250–1350 Ma, in good agreement with Rb‐Sr isochron ages of 1250 Ma obtained for the intrusives. The palaeogeographical position of Greenland was near equator with the major geographical axis orientated E‐W. Copyright © 1983, Wiley Blackwell. All rights reserved