THE TECTONIC HISTORY OF THE PACIFIC OCEAN BASIN SINCE CHRON 34Y (83 MA)

The present-day Pacific basin reflects the complex tectonic history of changes in plate boundary configuration. Since the birth of the Pacific plate in the Jurassic, the Pacific basin has witnessed a number of plate fragmentation and plate capture events, including the formation of the Vancouver, Nazca, and Cocos plates from the break-up of the Farallon plate, and the incorporation of the Bellingshausen, Kula, and Aluk (Phoenix) plates. In order to understand major plate reorganizations and the evolution of the circum-Pacific, kinematic models of the Pacific basin require a global context. Recent tectonic models have restricted their scope to small quadrants of the Pacific basin—here, we describe a new kinematic model for the entire Pacific basin that incorporates revised spreading histories, and explore the broad-scale implications for evolving plate motions across the Pacific basin and along circum-Pacific convergent margins. We quantitatively assess the seafloor spreading history in the Pacific basin since chron 34y (83 Ma) by deriving relative plate motions (with 95% uncertainties) for the Pacific-Farallon/Vancouver, Kula-Pacific, Bellingshausen-Pacific, and early Pacific-Antarctic spreading systems, based on a suite of recent data (fracture zone traces delineated from the latest gravity maps derived by satellite altimetry, and a large compilation of magnetic anomaly identifications). We find our well-constrained relative plate motions result in a good match to the fracture zone traces and magnetic anomaly identifications in both the North and South Pacific. In conjunction with recently published and similarly well-constrained relative plate motions for other Pacific spreading systems (e.g. Aluk-Antarctic, Cocos-Pacific, recent Pacific-Antarctic spreading), and embedded within a global plate model and its relative plate motion circuit, we explore the evolution of the Pacific basin since the Late Cretaceous. We focus on the implied convergence history along the North and South Americas, where we find that the inclusion of small tectonic plate fragments such as the Aluk plate along South America are critical for reconciling the history of convergence with onshore geological evidence.