Hydrous peridotitic fragments of Earth’s mantle 660 km discontinuity sampled by a diamond

The internal structure and dynamics of Earth have been shaped by the 660 km boundary between the mantle transition zone and lower mantle. However, due to the paucity of natural samples from this depth, the nature of this boundary—its composition and volatile fluxes across it—remain debated. Here we...

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Bibliographic Details
Published in:Nature geoscience 2022-11, Vol.15 (11), p.950-954
Main Authors: Gu, Tingting, Pamato, Martha G., Novella, Davide, Alvaro, Matteo, Fournelle, John, Brenker, Frank E., Wang, Wuyi, Nestola, Fabrizio
Format: Article
Language:English
Subjects:
704/2151/210
704/2151/330
704/2151/431
Chemical composition
Composition
Diamonds
Discontinuity
Earth
Earth and Environmental Science
Earth mantle
Earth science
Earth Sciences
Earth System Sciences
Enstatite
Geochemistry
Geology
Geophysics/Geodesy
Lower mantle
Mineral inclusions
Minerals
Spectrum analysis
Transition zone
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Summary:The internal structure and dynamics of Earth have been shaped by the 660 km boundary between the mantle transition zone and lower mantle. However, due to the paucity of natural samples from this depth, the nature of this boundary—its composition and volatile fluxes across it—remain debated. Here we analyse the mineral inclusions in a rare type IaB gem diamond from the Karowe mine (Botswana). We discovered recovered lower-mantle minerals ringwoodite + ferropericlase + low-Ni enstatite (MgSiO 3 ) in a polyphase inclusion, together with other principal lower-mantle minerals and hydrous phases, place its origin at ~23.5 GPa and ~1,650 °C, corresponding to the depth at the 660 km discontinuity. The petrological character of the inclusions indicates that ringwoodite (∼Mg 1.84 Fe 0.15 SiO 4 ) breaks down into bridgmanite (∼Mg 0.93 Fe 0.07 SiO 3 ) and ferropericlase (∼Mg 0.84 Fe 0.16 O) in a water-saturated environment at the 660 km discontinuity and reveals that the peridotitic composition and hydrous conditions extend at least across the transition zone and into the lower mantle. Hydrous conditions extend across the 660 km discontinuity between Earth’s mantle transition zone and lower mantle, according to analysis of a polyphase mineral inclusion in a gem diamond from the Karowe mine, Botswana
ISSN:1752-0894
1752-0908
DOI:10.1038/s41561-022-01024-y