The case for a chron 21 change in Africa absolute plate motion

Abstract

The India-Eurasia collision, a change in relative plate motion between Australia and Antarctica, and the coeval ages of the Hawaiian Emperor Bend (HEB) and Louisville Bend of ~chron 22--21 all provide convincing evidence of a global tectonic plate reorganization at chron 21. Yet if it were a truly global event, then there should be a contemporaneous change in Africa absolute plate motion (APM) reflected by physical evidence somewhere on the African plate. This evidence might be visible in the Réunion-Mascarene bend, which exhibits many HEB-like features such as a large angular change close to ~chron 21. Recently, the Réunion hotspot trail has been interpreted as a sequence of continental fragments with incidental hotspot volcanism. Here I propose the alternative hypothesis that the northern portion of the chain between Saya de Malha and the Seychelles (Mascarene Plateau) formed as the Réunion hotspot was situated on the Carlsberg Ridge, contemporaneously forming the Chagos-Laccadive Ridge on the India plate. I have created a 4-stage model that explores how a simple APM model fitting the Mascarene Plateau can also satisfy the age progressions and geometry of other hotspot trails on the African plate. This type of model could explain the apparent bifurcation of the Tristan hotspot chain, the age reversals seen along the Walvis Ridge and the diffuse nature of the St. Helena chain. To test this hypothesis we made a new African APM model that goes back to ~80 Ma using a modified version of the Hybrid Polygonal Finite Rotation Method. This method involves using seamount chains and their associated hotspots as geometric constraints for the model, and seamount age dates to determine its motion through time. The positions of the hotspots can be moved to get the best fit for the model and to explore the possibility that the chron 21 bend in the Réunion-Mascarene chain reflects African plate motion. I will examine how well this model can predict the key features reflecting African plate motion and contrast its predictions with other proposed models.