The African continental divide: Indian vs Atlantic Ocean spreading during Gondwana dispersal

Abstract:

It is well established that plate tectonic processes operate on a global scale and that spatially separate but temporally coincident events may be linked. However, identifying such links in the geological record and understanding the mechanisms involved remains speculative. This is particularly poignant during major geodynamic events, such as the dispersal of supercontinents where multiple axes of breakup may be present as well as coincident collisional events. To explore this aspect of plate tectonics, here, we present an analysis of the temporal variation in the mean half rate of seafloor spreading in the Indian and Atlantic Oceans, as well as plate kinematic attributes extracted from global plate tectonic models during the dispersal of Gondwana since ~200 Ma. Our analysis shows that during the ~20 Myrs prior to collision between India and Asia at ~55 Ma there was an increase in the mean rate of seafloor spreading in the Indian Ocean. This manifests as India rapidly accelerating towards Asia. This event was then followed by a prompt deceleration in the mean rate of Indian Ocean seafloor spreading after India collided with Asia at ~55 Ma. Throughout their existence, the mean rate of seafloor spreading in the Indian Ocean is generally greater than the Atlantic Ocean, and the period of fastest mean half spreading rate in the Indian ocean is coincident with a slowdown in mean half seafloor spreading rate in the competing Atlantic Ocean. We hypothesise that faster and hotter seafloor spreading in the Indian Ocean resulted in larger ridge push forces, which were transmitted through the African plate leading to a slowdown in Atlantic spreading. Following collision between India and Asia, and a slowdown of Indian Ocean spreading, Atlantic spreading rates consequently increased again. We conclude that the processes in the Indian and Atlantic oceans have likely remained coupled throughout their existence and that their individual evolution has influenced each other. This has implications for our understanding of spreading axis interaction and competition during supercontinent dispersal.