Researchers are discovering the Archaeological continental rocks in the southwest Indian ridge

Between the solid tectonic plates of the Earth above and its convection mantle below is a hot and soft layer known as the asthenosphere. At the mid-ocean ridges, the rise of the hot asthenosphere to the surface of the seabed creates a new oceanic crust.

Over time, the oceanic crust becomes older, cooler and denser and is eventually recycled back down into the mantle in the subduction zones. For this reason, the oceanic crust is usually less than 200 million years old.

A joint research team led by prof. Liu Chuanzhou of the Institute of Geology and Geophysics (IGG) of the Chinese Academy of Sciences has found abysmal peridotites dredged from the seabed along the southwest Indian Ridge, which are the oldest rocks in the ocean ever discovered. Another study revealed that they were derived from the neighboring African continent.

This work was published in Scientific advances on June 1.

These newly discovered rocks from the Indian Ocean are up to 2.7 billion years old and date back to what geologists call “Archean,” which comes from the Greek word for “ancient.” By analogy, the presence of these ancient rocks on a young ocean ridge is like finding your mother in her child’s kindergarten class. Fortunately, these strangely old mid-ocean ridges offer a clue as to their mysterious origins.

In addition, these ancient rocks have a highly refractory composition; in geochemistry refractory indicates a lack of fusible (ie, easily fusible) components in the mantle. Therefore, they are less like ocean materials and more like rocks from continents. The only possible explanation is that these rocks from the Archean mantle of the Indian Ocean were released and transported across the asthenosphere over 2,000 km to the mid-ocean ridge, where they were discovered.

Computer simulations were performed to test whether this assumed recycling mechanism actually worked. The modeling results indicate that the recycling process was highly efficient. As many as 20% of the continent could be removed in just 100 million years – geologically in the blink of an eye.

The old continental roots that appear at the bottom of the ocean clearly indicate that ocean plates are more complicated than previously thought. To decipher the Earth’s evolution, therefore, more attention needs to be paid to the ocean floor, which covers three-fifths of the Earth’s surface.

The study was conducted in collaboration with the Woods Hole Oceanographic Institution and the Max-Planck Institute of Chemistry.