The Earth’s mantle may not always move uniformly with the tectonic crust, challenging long-standing beliefs in geology. An international team of researchers stumbled upon this revelation while studying Easter Island, famous for its iconic Moai statues.
Historically, it was thought that convection currents in the mantle caused the crust to shift like a “conveyor belt.” This concept dates back to 1919, introduced by British geologist Sir Arthur Holmes. His idea explained how continents could drift apart, based on compelling evidence from matching geological features across distant landmasses.
However, these new findings from Easter Island’s ancient zircons—tiny crystals trapped in lava—suggest a more complicated picture. These zircons, some 165 million years old, indicate that certain sections of the mantle have remained stationary for millions of years, contradicting the conveyor belt theory.
Easter Island itself is geologically young, with its oldest features dating back about 2.5 million years to volcanic activity above an ocean plate. In their study, geologist Yamirka Rojas-Agramonte and her team aimed to date the island through the zircons but found an unexpected age discrepancy. While some crystals matched the island’s young volcanic activity, others dated back to before the island even existed.
Upon further analysis, they realized these ancient zircons originated deep within the mantle, where hot volcanic plumes rise, similar to what fuels volcanoes in Hawaii. This implies that the volcanic activity at Easter Island’s hotspot has been ongoing for 165 million years, despite the island’s young surface.
Current tectonic plates, however, have undergone significant changes over millions of years, becoming subducted and recycled in processes that complicate tracing their origins. Co-author Douwe van Hinsbergen raised an intriguing point: by reintegrating the ancient volcanic activity into geological simulations, it became clear that this evidence aligns with known phenomena such as mountain building and crust deformation.
Nevertheless, this puzzle deepens our understanding as the enduring presence of these ancient minerals suggests that the mantle behaves far differently than previously theorized. Instead of being a mobile conveyor belt, parts of the mantle may actually be more stationary, allowing these “time capsules” to exist and enhance our geological knowledge.
If confirmed, these findings would reshape our understanding of mantle dynamics—implying much slower movements than once assumed, and indicating that the mantle communicates with volcanic plumes in unexpected ways.
Reference
Rojas-Agramonte, Y., Pardo, N., Hinsbergen, D.J.J. van, Winter, C., Marroquín-Gómez, M.P., Liu, S., Gerdes, A., Albert, R., Wu, S., & Garcia-Casco, A. (2023). Zircon xenocrysts from Easter Island (Rapa Nui) reveal hotspot activity since the middle Jurassic. ESS Open Archive. https://doi.org/10.22541/au.170129661.17646127/v1