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

The image below shows Brú milli heimsálfa or the ‘Bridge between continents’. This is the constructive margin which runs through Iceland. To the left is the North American plate and to the right the Eurasian plate.

Brú milli heimsálfa or the ‘Bridge between continents’