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A joint research group has identified that the spatial scale of "heterogeneity" in the upper mantle, caused by a large-scale flow called a mantle plume rising from deep Earth, is less than 10 kilometers.

The research is in the journal Lithos. The team includes Senior Research Scientist Shiki Machida from the Next-Generation Marine Resources Research Center at Chiba Institute of Technology, Professor Kyoko Okino of the Atmosphere and Ocean Research Institute at the University of Tokyo, and researchers from the Graduate School of Engineering and the Department of Science and Technology at the National Museum of Nature and Science.

This finding is based on physical evidence from lava formed by volcanic activity at the Central Indian Ridge. Detailed chemical analyses of the lava confirmed that the cause of the heterogeneity was recycled material—rocks from plates that were once part of Earth's surface and had accumulated deep within Earth—which were directly transported to the upper mantle by mantle plumes.

Furthermore, by tracking compositional changes in lava that occurred during the movement of the mid-ocean ridge due to plate motion, the spatial scale of heterogeneity in the upper mantle was determined. The value of less than 10 km is approximately one-tenth or less of the previously estimated scale (on the order of 100 km) on the basis of seismic wave observations, indicating that the upper mantle is a structure where material mixes and homogenizes more rapidly than previously thought.

This achievement provides a new perspective on our understanding of Earth's internal structure and offers clues to the processes of material recycling within Earth's interior, akin to a form of "metabolism."