The subduction of the Farallon Plate beneath North America as derived from relative plate motions

High rates of subduction and near normal convergence of the Farallon plate correlate with the duration of the Laramide Orogeny in the Western Cordillera. The motion of the Farallon plate relative to North America is reconstructed back to the late Mesozoic using relative plate motion data. This reconstruction involves the use of a plate circuit in which each plate is linked to another with seafloor spreading information in order to relate converging plates. Two models for relative motions are considered. The preferred model predicts an increase in the subduction rate of the Farallon plate, exceeding 150 mm/yr, with a direction almost due east and perpendicular to the continental margin. The duration of this nonoblique (normal), high‐rate subduction correlates well with the duration of the Laramide Orogeny. This correlation must be regarded as only suggestive; the probable errors, when combined and propagated through the relative motion circuit, may be of the order of the effect observed. However, it is encouraging that these reconstructed Farallon/North American relative motions are similar to the published predictions of others, using the alternative, more direct approach of hot spot reconstructions.