Paleomagnetism of the Great Slave Supergroup, Northwest Territories, Canada: the Tochatwi Formation

Abstract

The Tochatwi Formation comprises some 800 m of fine-grained red to buff sandstone in the upper part of the Great Slave Supergroup. Recent geological work indicates an age of 1700 m.y., but this is not yet known with certainty. Results from 29 sampling sites stratigraphically covering the Tochatwi Formation are presented. Standard paleomagnetic techniques indicate that post-folding remagnetization is common, and this is confirmed by analysis of the magnetic vectors removed as partial thermal demagnetization proceeds. Two phases of remagnetization are recognized, one of which can be attributed to nearby Mackenzie-age intrusions. The other phase is equivalent to a remagnetization observed by other workers in Kahochella Group strata at localities 70 km away. As yet, the source of this remagnetization event cannot be identified. Eight sampling sites have escaped total remagnetization and an earlier, pre-folding remanence has been isolated from these (D = 030, I = −11, k = 14, α95 = 15°). The corresponding pole position (144W, 18S) is remote from those deduced from North American rocks of similar age, and possible explanations of this problem are discussed.