The asthenosphere is a hot and soft layer in between Earth's rigid tectonic plates above and its convecting mantle below. The hot asthenosphere upwelling to the surface of the seafloor forms new ocean crust.
After a while, the ocean crust becomes older, colder, and denser, and is recycled back down into the mantle at subduction zones. The ocean is less than 200 million years old.
The oldest rocks from the ocean ever found were dredged from the seafloor along the Southwest Indian Ridge. They were derived from the African continent.
Science Advances published this work on June 1.
The ancient rocks from the Indian Ocean are as old as 2 billion years and come from the Greek word for ancient. The mid-ocean ridge rocks offer a clue as to their mysterious origins.
These ancient rocks have a lack of fusible components in the mantle. They are more similar to rocks from the continents. The only possible explanation is that the Archean mantle rocks from the Indian Ocean were transported through the asthenosphere over 2,000 km to the mid-ocean ridge where they were discovered.
Computer simulations were conducted to see if the recycling mechanism could work. The results of the modeling show that the recycling process was very efficient. It could take as little as 100 million years to remove 20% of the continent.
Old continental roots are popping up on the ocean floor, indicating that the ocean plates are more complicated than previously thought. The ocean floor covers three-fifths of the Earth's surface.
The study was done in collaboration with the Woods Hole Oceanographic Institution.
More information: Chuan-Zhou Liu, Archean cratonic mantle recycled at a mid-ocean ridge, Science Advances (2022). DOI: 10.1126/sciadv.abn6749. www.science.org/doi/10.1126/sciadv.abn6749
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