What happens to the third arm of a rift during complete rifting of a continent?

During the complete rifting of a continent, the third arm of a rift typically becomes inactive as the tectonic forces that caused the rifting lead to the formation of two new tectonic plates that are separating. In a rift system, there are generally three arms at work, similar to the structure of a Y. As rifting progresses, one of these arms often fails to maintain significant geological activity or structural integrity, leading to a phase of inactivity.

The two remaining arms, which are more active, may continue to diverge, causing volcanic activity and the eventual creation of new oceanic crust if the rift evolves into a full ocean basin. While the tectonic activity can temporarily halt in the inactive arm, it does not mean that this section has completely halted the geological processes—rather, it signifies a shift in focus to the other regions that are actively contributing to the rifting process.

Understanding this concept is important in plate tectonics as it highlights the dynamic nature of continental break-up and the subsequent tectonic evolution that eventually leads to the formation of new ocean basins.