Iceland may be part of a submerged continent called Icelandia

Iceland could be the only exposed part of an entire continent, dubbed Icelandia, that is mostly submerged beneath the Atlantic Ocean. Gillian Foulger and her colleagues at Durham University have published this idea in the book In the Footsteps of Warren B. Hamilton: New Ideas in Earth Science.

Iceland lies on the Mid-Atlantic ridge, where two tectonic plates are slowly moving apart. Magma wells up along the ridge, before cooling and solidifying into rock, forming more seabed.

Earth’s outer layer, the crust, is typically thinner – about 6 to 7 kilometres – under the oceans than it is under continents, but Foulger says Iceland is an anomaly, as the crust beneath it is 40 kilometres thick. In general, geologists argue that the thickness of the crust can be explained by the presence of a so-called geological hotspot – an unusually hot region in the mantle that leads to greater volcanic activity.

But Foulger and her team have an alternative explanation. They argue instead that Iceland is made of continental crust and so are large areas of the surrounding seabed. This hidden continent of Icelandia, if it exists, has a surface area of 600,000 square kilometres.

Icelandia would be a relic of a time millions of years ago, when the continents that are now on opposite sides of the Atlantic Ocean were joined in a single supercontinent called Pangaea. The continents have since been pulled apart by the motion of the plates. However, Foulger thinks Icelandia is one chunk of Pangaean continental crust that survived and now sits underneath Iceland.

Foulger’s team has funding to collect very resilient crystals called zircons from Iceland. If the deeper rocks really are continental crust from Pangaea, the zircons should help support the idea. Continental crust is typically billions of years old, whereas oceanic crust – which is constantly created and destroyed – is usually no more than a few hundred million years old. So if the zircons beneath Iceland are older than this, they would support the team’s idea.

This story is based on an article in New Scientist.

Bill Gray