The formation of a global network of plate boundaries surrounding a mosaic of lithospheric fragments was a key step in the emergence of Earth’s plate tectonics. So far, propositions for plate boundary formation are regional in nature; how plate boundaries are created over thousands of kilometres in geologically short periods remains elusive. Here we show from geological observations that a >12,000-km-long plate boundary formed between the Indian and African plates around 105 Myr ago. This boundary comprised subduction segments from the eastern Mediterranean region to a newly established India–Africa rotation pole in the west Indian Ocean, where it transitioned into a ridge between India and Madagascar. We identify coeval mantle plume rise below Madagascar–India as the only viable trigger of this plate rotation. For this, we provide a proof of concept by torque balance modelling, which reveals that the Indian and African cratonic keels were important in determining plate rotation and subduction initiation in response to the spreading plume head. Our results show that plumes may provide a non-plate-tectonic mechanism for large-plate rotation, initiating divergent and convergent plate boundaries far away from the plume head. We suggest that this mechanism may be an underlying cause of the emergence of modern plate tectonics.

围绕岩石圈碎片镶嵌的全球板块边界网络的形成是地球板块构造出现的关键一步。到目前为止，板块边界形成的命题本质上是区域性的；板块边界是如何在地质短时期内形成数千公里的仍然难以捉摸。在这里，我们从地质观测中显示，大约 105 Myr 前在印度和非洲板块之间形成了一条 > 12,000 公里长的板块边界。该边界包括从东地中海地区到西印度洋新建立的印非自转极的俯冲段，在那里它过渡到印度和马达加斯加之间的山脊。我们确定马达加斯加-印度下方的同时代地幔柱上升是这次板块旋转的唯一可行触发因素。为了这，我们通过扭矩平衡模型提供了概念证明，这表明印度和非洲克拉通龙骨在确定板块旋转和俯冲起始以响应扩散的羽流头方面很重要。我们的研究结果表明，羽流可能为大板块旋转提供了一种非板块构造机制，在远离羽流头部的地方启动了发散和收敛的板块边界。我们认为这种机制可能是现代板块构造出现的根本原因。开始远离羽流头的发散和收敛板块边界。我们认为这种机制可能是现代板块构造出现的根本原因。开始远离羽流头的发散和收敛板块边界。我们认为这种机制可能是现代板块构造出现的根本原因。