ALBERT

Description: A vast ocean basin has spanned the region between the Americas, Asia and Australasia for well over 100 Myr, represented today by the Pacific Ocean. Its evolution includes a number of plate fragmentation and plate capture events, such as 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, which have been studied individually, but never been synthesised into one coherent model of ocean basin evolution. Previous regional tectonic models of the Pacific typically restrict their scope to either the North or South Pacific, and global kinematic models fail to incorporate some of the complexities in the Pacific plate evolution (e.g. the independent motion of the Bellingshausen and Aluk plates), thereby limiting their usefulness for understanding tectonic events and processes occurring in the Pacific Ocean perimeter. We derive relative plate motions (with 95% uncertainties) for the Pacific–Farallon/Vancouver, Kula–Pacific, Bellingshausen–Pacific, and early Pacific–West Antarctic spreading systems, based on recent data including marine gravity anomalies, well-constrained fracture zone traces 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 well-constrained relative plate motions for other Pacific spreading systems (e.g. Aluk–West Antarctic, Pacific-Cocos, recent Pacific–West Antarctic spreading), we explore variations in the age of the oceanic crust, seafloor spreading rates and crustal accretion and find considerable refinements have been made in the central and southern Pacific. Asymmetries in crustal accretion within the overall Pacific basin (where both flanks of the spreading system are preserved) have typically deviated less than 5% from symmetry, and large variations in crustal accretion along the southern East Pacific Rise (i.e. Pacific–Nazca/Farallon spreading) appear to be unique to this spreading corridor. Through a relative plate motion circuit, we explore 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 are critical for reconciling the history of convergence with onshore geological evidence.