Earth?s surface is comprised of a mosaic of rocky (lithospheric) plates. Motions of these plates give rise to major geologic features such as the Himalayas, the Alps, and the Atlantic Ocean. Unraveling the geologic history of plate motions is thus a matter of great importance to understanding the geologic history of our planet. For several decades, some have argued that trails of seamounts created at ?hot spots? such as Hawaii record the motions plates, and major changes of plate motion are indicated by features such as the great 50 million year old bend in the Hawaii-Emperor seamount chain. Others, however, have argued that seamount chains do not record ?absolute? plate motions (APM) because the hot spot sources as well as the plated move. An important question in this debate is whether hot spot trails on different plates can be reconciled with the known relative motions between plates in a common absolute motion model. A key problem is the motion of the Africa Plate. This project will reanalyze the absolute plate motion of Africa recorded using hot spot tracks to constrain plate motion and chronology. Broader impacts include the very high relevance of this study for understanding the most fundamental working of the planet, public dissemination of the results through a web site that includes podcasts, animations, etc, and training a graduate student.
Africa is a key plate in the global plate circuit, being surrounded by numerous plates across mid-ocean ridges. Relative motions between Africa and neighboring plates are thus well understood. However, the absolute plate motion (APM) of Africa may not be fully understood due to the diffuse nature of its hotspot trails and spare age data set. For instance, relative plate motions imply a major change in Africa motion for the 67-50 Myr time frame but this is not reflected in available APM models. One possibility is that all models have ignored using the Mascarene Plateaus as an extension of the Reunion trail. This has been done for good reasons: The Mascarene basin was spreading just before or at the same time as the hotspot trail would have been formed, and many suspect this trail to be partly formed by continental fragments with fortuitous basaltic overprinting. Finally, across the Carlsberg ridge we find the Chagos-Laccadive ridge which is the logical extension of the Reunion trail. However, presence of basalt and suitable ages along the Mascarene Plateau leaves a slim possibility that it might represent Africa plate motion. This was our hypothesis to be tested and we sought a model that could actually fit all Africa hotspot trails including the Reunion-Mascarene trail with its ~100 degree sharp bend (apparently coeval with the Hawaii-Emperor bend). While much of the latter may have its origin in plume motion, it would be intriguing if these two bends were formed at the same time, implying a global reorganization. A model satisfying all data was in fact developed. It fits all observations on the Africa plate and when projected across the Carlsberg ridge it fits the Chagos-Laccadive trail with its subtle bend at ~50 Ma. It implies a zig-zag reversal in Tristan-Walvis, matching observations of a double trail and their large age reversals, and fits the Canary trail's inverted C-shape. It even explains the location of 80 Ma Canary-type samples beneath the Madeiras Tore Rise and the terminus of the Bathymetrist chain. However, the model also implies high levels of net rotation during the 67-50 Myr time frame and apparently leads to unreasonably large changes in plate motions elsewhere when propagated through the global plate circuit. We are presently trying to reconcile the excellent fits to Africa data constrains and the implications of the model for global plate motions.
