Scientists have announced a discovery that could reshape how geologists understand the movement of tectonic plates. In a region south of Africa, researchers found rocks on the seafloor dating back 2.7 billion years. These ancient rocks appear to originate from the nearby African continent, a surprising find in a relatively young ocean ridge setting. The team from the Chinese Academy of Sciences remarked that discovering stones this old in a young maritime environment is like spotting a mother in a kindergarten, a vivid analogy used to describe the anomaly’s significance.
Between Earth’s solid tectonic plates and the convecting mantle lies the asthenosphere, a warm, partially molten layer that ranges in depth from about 40 to 660 kilometers. At mid-ocean ridges, basalt from the warm asthenosphere wells up to the seafloor, creating new oceanic crust and renewing the ocean floor.
As time passes, this oceanic crust cools and thickens, becoming denser. When it encounters a barrier, such as a continental plate, the denser oceanic material sinks beneath, reintroducing material from below to melt in the asthenosphere and rejoin the mantle. This process, known as subduction, generally keeps oceanic crust younger than roughly 200 million years.
However, a discovery emerged that did not fit the standard model. A joint research team led by Professor Liu Chuanzhou from the Institute of Geology and Geophysics of the Chinese Academy of Sciences found abyssal peridotites along the southwestern Indian Ocean ridge, especially south of Madagascar. This is notable because those rocks are the oldest ever found in the ocean. A subsequent study also identified material linked to the African landmass. The findings were published in Science Advances a number of weeks prior.
These exceptionally ancient rocks from the Indian Ocean are dated at 2.7 billion years old, belonging to the Archaean eon, a period geologists describe as ancient. Their presence on a relatively young mid-ocean ridge challenges established timelines. The researchers liken the discovery to encountering a mother in a kindergarten to illustrate how unexpected and revealing the find is. These extraordinarily old rocks offer clues about the forces that shaped Earth’s early oceans and crust.
Continental signatures on oceanic matter
Additionally, these ancient rocks show unusually refractory compositions. In geochemical terms, refractory means components that resist dissolution in the mantle. They resemble continental crust more than typical oceanic material.
How can this be explained? The authors suggest that rocks from the Indian Ocean’s archaean mantle could have fractured and traveled more than 2,000 kilometers to reach the mid-ocean ridge via the mantle’s asthenospheric conveyor. There they were found and studied, shedding light on deep Earth processes.
Computer simulations tested the proposed recycling mechanism and found the process to be highly efficient. In the model, it was possible for up to twenty percent of continental material to become submerged within a span of 100 million years—a geological blink of an eye by any measure.
Ancient continental debris recovered from the ocean floor demonstrates that oceanic plates may serve more intricate roles than previously understood. The researchers stressed that unraveling Earth’s evolution requires careful attention to the ocean floor, which covers roughly three-fifths of the planet’s surface.
The research was conducted in collaboration with the Woods Hole Oceanographic Institution and the Max Planck Institute for Chemistry. The study, described in detail in Science Advances, contributes to a broader understanding of plate tectonics and mantle dynamics, findings that are relevant for researchers and science enthusiasts across North America. This work underscores the importance of oceanic and continental interactions in shaping the planet’s geological history.
Reference: Science Advances, for the full study and data interpretation.
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