Great Slave Lake Supergroup paleomagnetism:Local rotations, apparent polar wander, true polar wander, or anomalous geodynamo?

English Abstract:

Previous paleomagnetic studies of Slave Craton, in northwestern Canada, revealed a sinuous apparent polar wander (APW) path referred to as the Coronation Loop, wherein paleomagnetic poles oscillate over 110° with ages ranging from ca. 1900 to 1850 Ma. We collected paleomagnetic samples across a broad region in the East Arm of Great Slave Lake (GSL), in order to determine if the rotations documented by the Coronation Loop are due to local structural anomalies, craton-scale tectonic motions or peculiar characteristics/behavior of the Orosirian geomagnetic field. Samples were collected at ~3m stratigraphic resolution over 700m of continuous homoclinal sections of the Tochatwi (red sandstone), Portage Inlet (mainly red siltstone), and Pearson (gray basalt) Formations. Paleomagnetic remanence commonly includes post-folding overprint signals of the Mackenzie Diabase (1270 Ma), which outcrops nearby, or the Hudsonian orogeny s.l. (1850-1750 Ma). We isolate a dual-polarity characteristic remanent magnetization (ChRM) direction that is generally shallow North or South in tilt-correct coordinates. Near the Portage Inlet / Pearson Formation contact, we sampled at several localities across folds that are likely related to movement on the McDonald fault at ca. 1850-1800 Ma; the ChRM passes the fold test at >99% statistical level. However, we observe ChRM declinations to vary by tens of degrees across the Christie Bay stratigraphy, even within homoclinal sections. This suggests that some of the previously recognized discordance of the GSL poles is due to APW, or perhaps geodynamo variations, as opposed to local structural rotations. If due to APW, whether it represents oscillatory true polar wander (as suggested by Mitchell et al., 2010, Precambrian Research) awaits similarly detailed paleomagnetic records from other cratons through this time period.