The middle mantle, a substantial portion of Earth's interior, is characterized by significant seismic heterogeneity, particularly in its velocity structure.
The middle mantle, lying between the upper and lower mantle, presents a complex picture based on seismic wave studies. Its key features revolve around variations in seismic wave velocities, indicating differences in composition, temperature, and density.
Seismic Heterogeneities
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Greater Dimensions of Seismic Heterogeneities: Compared to other layers, the middle mantle shows more pronounced seismic heterogeneities. These are variations in seismic wave speed, indicating differences in density, temperature, and/or composition.
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Low- and Medium-Velocity Domains: The existence of regions with lower and medium seismic wave velocities is a prominent feature. These could be indicative of partial melt, compositional differences, or temperature variations.
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High-Velocity Heterogeneities: These high-velocity zones, which are round or oval, can reach thousands of kilometers in size. These features are thought to represent subducted slabs of the Earth's crust that have sunk into the mantle.
Composition and Dynamics
While seismic data provides insight into the middle mantle's structure, understanding its precise composition and dynamics is still a topic of ongoing research.
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Material Exchange: The middle mantle likely plays a role in the exchange of material between the upper and lower mantle, impacting the overall dynamics of the Earth.
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Influence of Subduction: Subduction zones, where tectonic plates descend into the mantle, heavily influence the middle mantle, contributing to the observed heterogeneities.
In summary, the middle mantle stands out due to its significant variations in seismic wave velocities, suggesting complex compositional and thermal variations and its role in global geodynamic processes.
