rifting

Rifting is the tectonic process by which a region of the Earth's lithosphere is stretched and thinned, leading to the development of a rift valley and, in some cases, the initiation of seafloor spreading. It is driven by extensional tectonics and mantle dynamics, including upwelling magma and convection in the asthenosphere, which reduce crustal thickness and promote faulting. As thinning continues, large crustal blocks separate along normal faults, creating grabens and horsts.

Over time, rifting proceeds through stages: early faulting and tilting, development of linear rift basins, and, if spreading persists, the formation of a new ocean basin and a mid-ocean ridge. Volcanism is common during rifting, with basaltic magmatism intruding and erupting along faults. Sedimentation in growing basins records tectonic history, while faulting shapes topography and basin architecture.

Present-day examples include the East African Rift System, the Baikal Rift in Siberia, and the Rio Grande Rift in North America. The Red Sea and the Gulf of Aden are often cited as mature continental margins transitioning to seafloor spreading. Rifting operates over tens to hundreds of millions of years and significantly influences continental configurations, mineral and hydrocarbon basins, and regional seismicity. Understanding rifting helps explain the evolution of plate tectonics and the development of related geologic hazards.