Paleolatitudinal Drift and Major Rotation of the Wrangellia Superterrane in the Mesozoic: A Signal of East-Panthalassa Plate Motion?

The allochthonous origin of the Wrangellia superterrane relative to North America (NAM) has been established in the early days of plate tectonics using paleomagnetic and geologic data. However, orogenic deformation of the Wrangellia superterrane after its Cretaceous accretion to NAM has complicated the reconstruction of its pre-accretionary tectonic evolution. In particular, vertical-axis rotations linked to strike-slip faulting have cast doubt on the usefulness of paleomagnetic declinations in deciphering its pre-accretionary motions. Here, we compile paleomagnetic data from the Wrangellia superterrane and present new results from uppermost Triassic limestones and lowermost Jurassic lavas of the Bonanza arc, which confirm that it was at those times at a much lower latitude than today (∼50°–60°N), at a latitude of either ∼25°–30°N or ∼25°–30°S. Moreover, declinations reveal a coherent, major clockwise or counterclockwise rotation, depending on hemispheric origin. When correcting for previously documented true polar wander at the approximate longitude of the Wrangellia superterrane at ∼190 Ma, new and existing paleomagnetic data allow for two possible scenarios of Mesozoic kinematic evolution: from 190 to 80 Ma, in the southern hemisphere scenario, the Wrangellia superterrane was transported ∼5,000 km northward while rotating ∼110° clockwise with an associated north-dipping subduction zone, while in the northern hemisphere scenario it remained at northern middle latitudes while rotating ∼70° counterclockwise at a south-dipping subduction zone. The southern hemisphere scenario appears more plausible when tested against recent reconstructions of minimum oblique convergence beneath NAM and mantle tomography images of slab remnants.