Coronation loop resurrected: Oscillatory apparent polar wander of Orosirian (2.05-1.8 Ga) paleomagnetic poles from Slave craton

The Coronation loop is a 110 degrees arcuate sweep of 15 paleomagnetic poles with ages of ca. 1950-1850 Ma, derived from contemporaneous basins on the western (Coronation), southern (Great Slave) and eastern (Kilohigok) margins of the Slave craton in the northwestern Canadian shield. Although the paleomagnetic results are either demonstrated as primary or most parsimoniously interpreted as such, it is likely they were subsequently rotated shortly after deposition during conjugate transcurrent faulting along the conjugate McDonald (Great Slave) and Bathurst (Kilohigok) strike-slip fault systems. No rotation is expected of poles from the epicratonic Coronation margin. Previous analyses have debated the amounts of local rotations in the other basins, with one end-member view that the spread in paleomagnetic poles is entirely due to local rotations. Here we propose that, relative to the principal axis of compression for conjugate faulting, the far-field Bathurst and McDonald fault systems have rotated (equally and oppositely) 12 degrees to widen an original 60 degrees geometry to the present-day 84 degrees angle. We rotate pre-1840 Ma poles from the immediate (similar to 50 km) environs of these faults 12 degrees CCW (Bathurst) and CW (McDonald). This simple structural retrodeformation brings time-correlative poles from the Kilohigok and Great Slave basins into agreement. As independent support for this modest amount of local rotations, paleocurrent measurements from the Great Slave basin, from sections interspersed among paleomagnetic sampling localities and elsewhere, indicate that large vertical-axis rotations have not taken place. Our restoration of the Coronation loop to Slave's cratonic reference frame slightly increases its angular sweep and implies rapid polar wandering that is irreconcilable with plate tectonic rates of motion. We interpret the Coronation loop as a signal of rapid, oscillatory true polar wander (TPW), which suggests that Archean-Paleoproterozoic supercratons modulated mantle topology in much the same manner as recent supercontinents Rodinia and Pangea. (C) 2010 Elsevier B.V. All rights reserved.