Northeast-trending Early Proterozoic dykes of southern Superior Province: multiple episodes of emplacement recognized from integrated paleomagnetism and U–Pb geochronology

Abstract

Integrated paleomagnetic and U–Pb geochronologic studies have been conducted to establish the paleomagnetic directions and ages of Early Proterozoic tholeiitic dykes of northeast trend in the southern Superior Province, previously referred to collectively as Preissac dykes. It is demonstrated that they are readily separated on the basis of paleomagnetism into subsets, referred to as the Biscotasing and Senneterre swarms. In addition a pair of unnamed dykes may be associated with the north-and northwest-trending Matachewan swarm farther west.Biscotasing dykes have a down-west magnetization of single polarity with a corresponding paleopole at 27.8°N, 136.7°W (dm = 12.3° and dp = 9.4°). Senneterre dykes carry an up-north (or occasionally down-south) direction with corresponding paleopole at 15.3°S, 75.7°W (dm = 7.0°, dp = 4.4°). The Senneterre direction is indistinguishable from the primary N1 remanence direction that dominates the magnetization of Nipissing sills of the Southern Province. Paleomagnetic field tests described herein or in earlier studies indicate that Biscotasing and Senneterre directions are primary and, hence, that two ages of intrusion are involved, with the age of Senneterre dykes coinciding with the intrusion of most Nipissing sills. U–Pb dating of baddeleyite conducted at a paleomagnetic sampling site yields an age of 2214.3 ± 12.4 Ma for the Senneterre swarm, indistinguishable from the age of 2217.2 ± 4 Ma reported from an N1 Nipissing sill site in another study. A U–Pb age on baddeleyite and zircon of 2166.7 ± 1.4 Ma was obtained from a paleomagnetic site in the Biscotasing swarm. The primary paleopoles for the Senneterre, Nipissing, and Biscotasing rocks define a direction of polar wander opposite to that of the most widely used polar wander paths for North America for this period, suggesting that these paths should no longer be used.

Large igneous provinces (LIPs), giant dyke swarms, and mantle plumes: significance for breakup events within Canada and adjacent regions from 2.5 Ga to the PresentThis article is one of a selection of papers published in this Special Issue on the the theme Lithoprobe—parameters, processes, and the evolution of a continent.Lithoprobe Contribution 1482. Geological Survey of Canada Contribution 20100072.

“…The 2170 Ma (2167 ± 1, 2168 ± 2, 2172 ± 1 Ma) Biscotasing swarm (Buchan et al 1993;Halls and Davis 2004;Halls et al 2005) is a major linear dyke swarm that cuts across a large portion of the Superior craton (Fig. 6r).…”

Proterozoic diabase sills of northern Ontario: Magnetic properties and history

“…That path has been corroborated many times and refined with the benefit of improved laboratory instrumentation in the intervening years [e.g., Halls, 1979, 1983;Palmer et al, 1981] notably reviewed for the rocks of interest here by Halls and Pesonen [1982]. Precisely dated paleopoles are available for rocks on an earlier part of the apparent polar wander path for adjacent areas by Buchan et al [1993Buchan et al [ , 1996 and in the context of global reconstructions [Buchan et al, 2000]. Cropping out on islands in Lake Superior, the Osler Volcanic Series places the magnetostratigraphy of the underlying diabase intrusions in a stratigraphic context JOURNAL OF GEOPHYSICAL RESEARCH, VOL.…”

Apparent polar wander paths and the close of late Archean crustal transpression, northern Ontario

“…Track 2 is more modern and is based mainly on postmetamorphic dikes from adjacent study areas (Figure 1a). It is particularly useful in precise paleogeographic reconstructions for the late Archean‐Proterozoic transition 2400–2000 Ma [ Buchan et al , 1993, 1996, 2000, 2001]. Moreover, the paleomagnetic data correspond with sites where U/Pb geochronology fixed ages with 95% confidence limits of approximately ±2 Ma, providing a sound APWP for the Archean‐Paleo‐Proterozoic transition.…”