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The formation and preservation of compositional heterogeneities inside the Earth affect mantle convection patterns globally and control the long-term evolution of geochemical reservoirs. However, the distribution, nature, and size of reservoirs in the Earth’s mantle are poorly constrained. Here, we invert measurements of travel times and amplitudes of seismic waves interacting with mineralogical phase transitions at 400–700-km depth to obtain global probabilistic maps of temperature and bulk composition. We find large basalt-rich pools (up to 60% basalt fraction) surrounding the Pacific Ocean, which we relate to the segregation of oceanic crust from slabs that have been subducted since the Mesozoic. Segregation of oceanic crust from initially cold and stiff slabs may be facilitated by the presence of a weak hydrated layer in the slab or by weakening upon mineralogical transition due to grain-size reduction.
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How lowermost mantle viscosity controls the chemical structure of Earth’s deep interior
Abstract Determining the fate of subducted oceanic crust is critical for understanding material cycling through Earth’s deep interior and sources of mantle heterogeneity. A key control on the distribution of subducted slabs over long timescales is the bridgmanite to post-perovskite phase transition in the lowermost mantle, thought to cause rheological weakening. Using high-resolution computational models, we show that the ubiquitous presence of weak post-perovskite at the core-mantle boundary can facilitate or prevent the accumulation of basaltic oceanic crust, depending on the amount of weakening and the crustal thickness. Moderately weak post-perovskite ( ~ 10–100× weaker) facilitates segregation of crust from subducted slabs, increasing basalt accumulation in dense piles. Conversely, very weak post-perovskite (more than 100× weaker) promotes vigorous plumes that entrain more crustal material, decreasing basalt accumulation. Our results reconcile the contradicting conclusions of previous studies and provide insights into the accumulation of subducted crust in the lowermost mantle throughout Earth’s history.
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- PAR ID:
- 10480818
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Communications Earth & Environment
- Volume:
- 4
- Issue:
- 1
- ISSN:
- 2662-4435
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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