A global-scale plate reorganization event at 105−100 Ma

Abstract

A major plate reorganization is postulated to have occurred at approximately 100Ma. However, this reorganization has received limited attention, despite being associated with the most prominent suite of fracture zone bends on the planet and many other geological events. We investigate tectonic events from the period ∼110 to 90Ma and show that the reorganization occurred between 105 and 100Ma, was global in scale, and affected all major plates. Seafloor evidence for plate motion changes is abundant during this period, with either fracture zone bends or terminations preserved in all ocean basins. Long-lived eastern Gondwanaland subduction ended along a 7000km long section of the margin, while elsewhere around the proto-Pacific rim subduction continued and there is evidence that compressional stresses increased in the overriding plates. Thrusting in western North America, transpression and basin inversion in eastern Asia, and development of the present-day Andean-style margin along western South America occurred contemporaneous with the development of an extensional regime in eastern Gondwanaland. Basin instability in Africa and western Europe further demonstrates that lithospheric stress regime changes were widespread at this time. Considering the timing of the reorganization and the nature of associated plate boundary changes, we suggest that eastern Gondwanaland subduction cessation is the most likely driving mechanism for the reorganization. Subduction is the dominant driver of plate motion and therefore this event had the potential to strongly modify the balance of driving forces acting on the plates in the southwestern proto-Pacific and neighboring plates, whereby producing widespread changes in plate motion and continental lithospheric stress patterns. We propose that major changes in ridge–trench interaction triggered the cessation of subduction. The progressive subduction of two closely spaced perpendicular mid ocean ridges at the eastern Gondwanaland subduction zone, to the east of Australia and New Zealand, respectively, resulted in very young crust entering the trench and we suggest that by 105−100Ma there was insufficient negative buoyancy to drive subduction. Finally, we propose that the plume push force of the Bouvet plume, that erupted near the African–Antarctic–South American triple junction, contributed to plate motion changes in the southern Atlantic region.