How do continental-rift eruptions form flood basalts?

Flood basalts are large igneous province formed by the eruption of vast quantities of molten rock onto the Earth's surface. They consist of numerous individual basalt lava flows that can cover thousands of square kilometers. Typically, flood basalts occur in continental settings, where a series of fissure eruptions give rise to extensive lava plateaus.

Continental rifting is a process where the lithosphere is stretched and thinned, leading to the formation of rift valleys. It occurs when tectonic forces pull apart the Earth's crust, allowing the mantle to rise and melt due to a decrease in pressure. The molten rock (magma) then rises through the crust and erupts onto the surface, causing rift-related volcanic activity.

Mantle plumes are upwelling of hot, buoyant material from deep within the Earth's mantle. They are thought to be responsible for the initiation of continental rifting in many cases. When a mantle plume is present, it can cause the overlying lithosphere to gradually thin and weaken, making it more susceptible to rifting and associated volcanic activity. The presence of a mantle plume can supply a significant amount of heat and magma to the rift zone, promoting the formation of flood basalts.

As the continental crust is stretched and pulled apart during rifting, a network of fissures may develop. These fissures provide pathways for molten rock to rise from the mantle to the Earth's surface. Due to the large-scale nature of continental rifting, these fissures can be extensive, leading to widespread volcanic activity and the eruption of large volumes of basaltic lava.

During a rift eruption, magma rises along the fissures and erupts onto the Earth's surface, typically as low viscosity basaltic lava. These eruptions can be highly effusive, meaning that large quantities of lava are released with low explosive potential. The low viscosity nature of the basaltic lava allows it to flow over large distances, sometimes covering vast areas of land. As lava accumulates, numerous individual lava flows eventually form extensive flood basalt provinces. In conclusion, continental-rift eruptions form flood basalts through a series of processes involving the stretching and thinning of the lithosphere, the contribution of mantle plumes, the formation of fissures, and the eruption of low viscosity basaltic lava. These processes come together to create vast, widespread eruptions that result in the emplacement of flood basalt provinces.