Aging Subduction Zones: Water Storage Capacity in Oceanic Crust Slabs Expands, Researchers Reveal

06/07/2023

Article by: Andacs Robert Eugen, on 06 July 2023, at 03:20 am PDT

In a ground-breaking discovery, an international research team has uncovered a crucial link between the age of subduction zones and their ability to recycle water between the Earth's surface and its inner layers. The team's findings, published in the journal Geology on July 1, 2023, challenge previous assumptions and provide valuable insights into the complex processes governing water and mass recycling in tectonic settings.

When tectonic plates collide, and one plate subducts beneath the other, rocks within the subduction zone undergo metamorphosis due to changes in pressure, temperature, and chemical environments. This transformative process plays a vital role in recycling water and essential elements between the Earth's surface and its deep interior.

Lawsonite eclogites, a type of rock that forms under high pressure, are particularly significant in water storage within subducting plates. These rocks contain the mineral lawsonite, which can harbor substantial amounts of water, transporting it to the deeper mantle.

Traditionally, scientists believed that oceanic crust transforms into lawsonite eclogites in cold subduction zones based on models and experiments. However, the team's research challenges this assumption. Fossilized subduction zones on the Earth's surface rarely contain lawsonite, raising questions about our understanding of water storage in these zones.

To unravel this puzzle, Dr. David Hern√°ndez Uribe from the University of Illinois Chicago and Professor Tatsuki Tsujimori from Tohoku University led a team that utilized advanced modeling techniques to simulate rock formation at different stages of a subduction zone's lifetime.

Through petrological modeling and phase equilibrium calculations, the researchers made a striking discovery. They found that in the early stages (< 6 million years) of a subduction zone, the oceanic crust does not transform into lawsonite eclogites. However, as the subduction zone matures (12-33 million years), this transformation occurs.

"Our study revealed that the formation of lawsonite eclogites is dependent on the maturity of the subduction zone," explains Tsujimori. "Lawsonite's role in recycling water beneath the Earth's surface is significant only in mature subduction zones. In younger zones, its impact is less pronounced than previously believed."

These findings enhance our understanding of water and mass recycling within tectonic settings. Subducting tectonic plates in the early stages of subduction zones will carry less water compared to those in mature stages. This knowledge contributes to a more comprehensive comprehension of the dynamic processes occurring beneath our planet's surface and their implications for Earth's overall geological evolution.

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