A revised kinematic model for the relative motion between Pacific oceanic plates and North America since the Late Cretaceous

Abstract

The convergence between the Pacific, Farallon, and Kula oceanic plates and the North American plate has provided a driving force for tectonic processes that have shaped the western margin of North America. Yet reconstructions of plate motion in the Pacific basin have traditionally relied on the assumption of fixed hot spots. In the last decade, substantial Cretaceous to Paleogene motion between the Pacific and Atlantic hot spots has been recognized, providing motivation to reevaluate the history of relative motion between Pacific oceanic plates and North America by means of plate circuit reconstructions. This paper presents new kinematic models based on two alternative plate circuits linking the Pacific plate to North America since Late Cretaceous time. When compared to models relying on fixity of Pacific and Indo‐Atlantic hot spots, our reconstructions suggest that the Pacific‐Kula and Pacific‐Farallon ridges were ∼600–1000 km closer to the western margin of North America and hence that the Farallon and Kula plates were smaller in Late Cretaceous to middle Eocene time. These findings cast significant doubt on the viability of a configuration of the Farallon‐Kula ridge that juxtaposes the Kula plate with the southern part of the paleo‐North American margin during this time interval. The results of our new reconstructions also suggest more oblique convergence between the Farallon (or Kula) plate and North America from the Late Cretaceous to the middle Eocene related to the combination of dominantly northwest motion of the Pacific plate and steady southwest motion of North America. This provides an efficient mechanism for the coast‐parallel translation of some accreted terranes of North America. It may also explain the structure of geological units in western North America, such as the Central Belt of the Franciscan Complex, which show a dominant coast‐parallel fabric formed during an interval coeval with the episode of oblique convergence.