Easter Island is interesting in more ways than one: for its astonishing collection of giant statues, but also for its volcanic rock formations. These latter actually present a form of temporal contradiction. At 2.5 million years old, they contain very old minerals. But a team of researchers has found the answer to this mystery well.
If Easter Island is famous for its sculptures, it also has a lot of interest. GeologistsGeologists. It is actually a volcanic island in the Pacific Ocean, formed by the eruption of a hotspot volcano 2.5 million years ago. The island is actually part of a chain of islands and underwater volcanoes that stretches for 2,700 km. As a reminder, these volcanic chains are created by the movement of an oceanic plate over a magmatic plume, considered fixed, that rises from its base. coatcoat.
165 million year old minerals in very small lavas!
However, a team of researchers has uncovered a strange temporal discrepancy: if the lavas were indeed erupted 2.5 million years ago, they MineralsMinerals Called ZirconsZirconswhich is 165 million years old. The mystery deepened when chemical analyzes revealed that the zircons came from the same magmatic source as the island’s current volcanoes. However, it has been completely ruled out that the Easter Island volcanoes were active 165 million years ago, simply because the oceanic plate that PortPort…didn’t exist at the time!
To solve this puzzle, the researchers simulated movementmovement Plates and possible associated volcanic activity in the past. It thus appeared that 165 million years ago, where Easter Island is now located, was occupied by a vast volcanic plateau that arose from the hotspot. This plateau is almost certainly gone today, having passed under the Antarctic plate 110 million years ago.
A much older hotspot and a coat less mobile than previously thought.
This scenario is particularly interesting because it allows us to describe a phase of deformation. The crystThe cryst Antarctica at this exact time, which would be associated with entry into the subduction zone of the magmatic plateau. These results, published on the site ESS Open Archive (but not yet peer-reviewed), suggest that the Easter Island hotspot has been active for a very long time, which helps explain the presence of 165-million-year-old zircons in much younger lavas. These minerals, which formed during the previous volcanic event, were actually preserved within the mantle all this time before being carried away with the new one. MagmaMagma Born during the formation of Easter Island.
However, this hypothesis has an important geodynamic implication: it requires that the currents that permanently drive the mantle are slower than previously thought. Otherwise, the zircons that formed 165 million years ago would have been transported further away and gone undetected. Volcanic rocksVolcanic rocks From Easter Island.