Paleomagnetism of the Katherine Group in the Mackenzie Mountains: implications for post-Grenville (Hadrynian) apparent polar wander

Abstract

Paleomagnetic poles from the Upper Proterozoic Mackenzie Mountains supergroup (MMs) of northwestern Canada define an apparent polar wander path lying to the west of the Grenville Loop. This path is suggested from an analysis of the quartzitic Katherine Group, whose probable primary pole lies at the beginning of the sequence, near the younger end of the Grenville Track (0.88 Ga). The end of the apparent polar wander (APW) sequence may be defined by a primary pole from sills intruding the Tsezotene Formation below the Katherine. We relate the sills, dated at about 0.77 Ga, to the rifting event that led to "Copper cycle" and Rapitan sediments above the MMs, and we suggest that the exposed part of the MMs has an age between 0.88 and 0.77 Ga. The APW path is apparently not affected by rotations: pole evidence indicates little if any relative rotation between thrust sheets of the fold belt or between the fold belt and the craton.Paleomagnetic analysis of the Katherine Group data, obtained by alternating field, thermal, and chemical methods, revealed three magnetizations. The probable primary remanence, KA, carried by mainly detrital hematite grains, has a direction of D, I = 267", +21° (N = 13 specimens, k = 33, a,, = 7") and a-pole at 9"N, 210°W (6,, 6, = 4", 8"). A secondary component, KB, carried by hematite pigment, has a direction of D, I = 258", +42" (N = 4 sites, k = 326, a,, = 5") and a pole at 17"N, 196"W (6,, 6, = 4", 6"). It documents further a pervasive overprint magnetization found in most MMs rocks. A similar hematite magnetization is probably primary in the overlying Copper cycle rocks. The youngest component, Kc, is found partly in a second, probably largely post-folding pigment phase (post-Late Cretaceous or Paleocene) and has a direction of D, I = 007", +84" (N = 9 sites, k = 77, a,, = 6") and a pole at 77"N, 122"W (S,, 6, = 11°, 12").Les p8les palComagnCtiques du supergroupe Mackenzie Mountains (MMs), d'iige protCrozoique, du nord-oeust du Canada ddfinissent une courbe de dCrive apparente des p8les passant a l'ouest de la boucle du Grenville. Cette courbe est dCduite d'une analyse du groupe quartzitique Katherine, dont le p81e primaire probable est attribuC au dCbut de la sCquence, correspondant approximativement a 1'extrCmitC la plus jeune de la courbe du Grenville (0,88 Ga). L'extrCmitC de la courbe de la dCrive apparente des p8les de la sCquence peut &re dCfinie par le p81e primaire des filons-couches qui recoupent la formation Tsezotene sous-jacente au groupe Katherine. Les filons-couches datCs a 0,77 Ga sont reliCs a I'evCnement de rifting qui est responsable de la prksence du "cycle de cuivre" et des sCdiments Rapitan sus-jacents au MMs, et ils indiquent pour les alleurements du MMs un ige compris entre 0,88 et 0,77 Ga. La courbe de la dCrive apparente des p8les ne semble pas avoir subi par des rotations; 1'Ctude des p8les rCvkle que s'il y a eu rotation entre les nappes de charriage de la zone plissCe ou entre la zone plissCe et le craton, elle n'a pu &re que trks restreinte.Les analyses palCo...

Crustal-scale ramp in a Middle Proterozoic orogen, Northwest Territories, Canada

“…Together, the sedimentary rocks of sequence A in the Coppermine Homocline and the Wernecke Mountains are interpreted as a westwardthickening platform to miogeoclinal wedge of strata that was deposited onto older crystalline basement of the Wopmay Orogen (Kerans et al 1981 ;Young 1984 thick, with an unexposed base (Eisbacher 1981). and the age of the exposed portion is between about 0.88 and 0.78 Ga (Park and Aitken 1986;Jefferson and Parrish 1989). The Pinpicula Group is about 3.5 km thick.…”