Recent research on the extinct volcanoes surrounding Rapa Nuibetter known as Easter Island, calls into question some elements of the traditional theory on the movement of the Earth’s tectonic plates. According to the commonly accepted view, tectonic plates move on a layer of viscous rock called coatsimilar to a conveyor belt. This idea, initiated in 1912 by Alfred Wegener with his theory of continental drift, was accepted by the majority of scientists only towards the middle of the 20th century. However, new studies suggest that the issue is more complex than previously thought.
In 2019, a group of Cuban and Colombian geologists traveled to Turnip Nui with the aim of determining the precise age of the island’s volcanic origins, using the mineral zircon. This mineral is particularly useful for geological dating because it crystallizes as the magma cools, allowing the age to be established based on the radioactive decay of uranium into lead. Although they expected to find zircons formed around 2.5 million years ago, when the island’s first lavas were deposited, the team was surprised to discover that the crystals they found dated back up to 165 million years ago.
The chemical analyzes of the czircon crystals showed that they all had a similar composition, which indicated that they came from magma similar to that of current volcanoes. However, it is impossible that those volcanoes were active 165 million years ago, since the plate they rest on is not even that old.
Mantle plumes and doubts about the Great Conveyor Belt theory
The most plausible explanation suggested by the team is that the minerals come from aancient source of volcanism in the Earth’s mantle beneath the plate, long before current volcanoes formed. However, this hypothesis raises further questions. Rapa Nui is believed to be the product of a “mantle plume“, a giant column of hot molten rock that transports material from the depths of the mantle to the Earth’s surface. Mantle plumes are thought to remain fixed as tectonic plates shift above them, generating new volcanoes with each plate movement.
To get more information, the researchers involved Douwe van Hinsbergena geologist at Utrecht University, who added a vast volcanic plateau to tectonic simulations of the region. The results obtained suggest that the Rapa Nui plume may have been present for about 165 million years, and the ancient zircons may have been “recycled” from the depths of the Earth together with younger magmas during volcanic eruptions.
The new findings open further debate about whether the mantle may be moving much more slowly than tectonic plates, complicating the traditional theory of “Large Conveyor Belt“. Research conducted by the team in other areas, such as the Galápagos Islands and New Guinea, has already provided clues that the Earth’s mantle may be slower than expected, but further investigations are needed to confirm this hypothesis.
