Newswise — A research team comprised of international scientists has made a significant discovery regarding the impact of a subduction zone's age on its ability to recycle water between the Earth's surface and its inner layers. The team's findings were published in the journal Geology on July 1, 2023.
When two tectonic plates converge and one plunges beneath the other in a process known as subduction, various rocks undergo metamorphosis due to changes in pressure, temperature, and chemical environments. This metamorphic process plays a crucial role in recycling water and essential elements such as strontium, uranium, thorium, and lead between the Earth's surface and its deep interior.
Lawsonite eclogites, a type of rock that forms under high pressure, are particularly important in storing water within subducting plates. These rocks contain the mineral lawsonite, which can hold substantial amounts of H2O and transport it to the deeper mantle.
Conventionally, scientists believed that oceanic crust transforms into lawsonite eclogites in cold subduction zones. This assumption was based on models and experiments indicating that lawsonite is a prevalent mineral in cold geothermal environments. However, the reality is quite the opposite. Lawsonite is not commonly found in fossilized subduction zones on the Earth's surface, which raises further questions about our current understanding of how water is stored in these subduction zones.
To unravel this perplexing puzzle, a team led by Dr. David Hernández Uribe from the Department of Earth and Environmental Sciences at the University of Illinois Chicago and Professor Tatsuki Tsujimori from the Center for Northeast Asian Studies at Tohoku University employed advanced modeling techniques to simulate rock formation at different stages of a subduction zone's lifetime.
By conducting petrological modeling and phase equilibrium calculations, the research team discovered that oceanic crust does not transform into lawsonite eclogites during the early stages (< 6 million years) of a subduction zone. However, as the subduction zone matures (between 12 and 33 million years), the transformation occurs.
"Our findings indicate that the formation of lawsonite eclogites depends on the maturity of the subduction zone," explains Tsujimori. "Lawsonite only plays a significant role in recycling water deep beneath the Earth's surface in mature subduction zones. In younger zones, its influence is not as substantial as previously believed."
This discovery will contribute to scientists' understanding of water and mass recycling in tectonic environments. It suggests that tectonic plates subducting in the early stages of a subduction zone's history will not transport as much H2O as plates subducting in the later, more mature stages of the subduction zone's lifetime.
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