Assessing the conditions of continental breakup at magma-poor rifted margins: What can we learn from slow spreading mid-ocean ridges?

We propose a review of the tectonic, magmatic and hydrothermal evolution of slow spreading ridges, focusing on concepts which we think are most relevant to discuss the rift to drift transition at magma-poor ocean–continent transitions (OCTs). Based on this review, we emphasize the importance of the thermal regime as a key parameter and we propose that the thermal regime of magma-poor OCTs evolves in the following principal phases: the onset of decompression mantle melting, the onset of localized plate divergence, the installation of a ridge-type thermal regime (active heat balance, no inheritance), which we argue is the most practical definition for continental breakup, and, possibly, the onset of ridge-type, focused mantle upwelling. We propose this phased evolution as a framework in which to develop further research, combining our understanding of rifting and seafloor spreading, in order to better quantify the processes that control continental breakup.