A constructive (tensional) plate boundary happens where plates move apart. Most of these plate margins are under the oceans. As the plates move apart magma rises from the mantle to the Earth’s surface. the rising magma forms shield volcanoes.
A constructive plate margin
Constructive (tensional) plate margins occur where plates move apart. Examples below include the South American Plate and African Plate and the Eurasian Plate and the North American Plate.
The Earth’s main plates