This experimental finding overturns decades of accepted geological theory regarding serpentinite dehydration and indicates that deep-Earth water transport efficiency can reach nearly 90%, carrying up to three times more water into the mantle than previous models estimated.
High-Pressure Experiments at International Accelerator Facilities
For decades, standard geological models maintained that as serpentinite moved deeper into subduction zones, rising temperatures and pressures triggered dehydration reactions. These processes were thought to force stored water back toward the Earth's surface.
By exposing mineral samples to extreme, high-pressure and high-temperature environments that mimic the Earth’s deep interior, the researchers observed that dehydration behavior varies dramatically depending on thermal conditions within the subducting plate. The experiments revealed that traditional water release is not universal across all subduction zones.
Thermal Variations Dictate Deep-Earth Water Storage
At the relatively warm plate boundary known as the "Cold Moho," dehydration reactions occur at a depth of approximately 220 kilometers. According to the experimental data, this specific reaction increases rock density by roughly 16 percent and accelerates P-wave seismic velocities by about 10 percent.
In contrast, the researchers observed a completely different mechanism within the colder core of the subducting plate, designated as the “Cold Core” or “Ultracold Moho” environment. At roughly 280 kilometers depth, serpentinite decomposes to form a new hydrous mineral phase in what the team terms an “super-hydrated decomposition reaction.” Within this colder regime, the rock’s water content jumps from an initial 13 weight percent to as high as 19 weight percent. Simultaneously, rock density increases by approximately 10 percent, and seismic wave speeds rise by 7 percent.
Implications for Global Water Cycles and Geodynamics
These divergent pathways demonstrate that subducting slabs do not act as simple, leaky conveyor belts. Instead, local temperature and moisture conditions allow certain zones within a descending plate to lock away fluids that would otherwise escape toward the crust.
This revised understanding of deep-Earth hydrology provides geologists with new constraints for modeling global water cycles. By establishing precise pathways and storage capacities for fluids descending into the mantle, the findings offer vital parameters for interpreting large-scale geological phenomena, including volcanic activity and earthquakes linked to subduction zones.
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