Publikationsdatum:
2014-02-28
Beschreibung:
Nature Geoscience 7, 224 (2014). doi:10.1038/ngeo2074 Authors: M. Nishi, T. Irifune, J. Tsuchiya, Y. Tange, Y. Nishihara, K. Fujino & Y. Higo The presence of water strongly influences the structure, composition and dynamics of the Earth’s deep mantle. Hydrous magnesium-rich silicates play an important role in transporting water into the deep mantle when oceanic plates subduct as slabs. The highest-pressure form of such hydrous silicates, phase D, was reported to dissociate into an assemblage of nominally anhydrous phases plus water at pressures of about 44 GPa, equivalent to 1,250 km depth. In this way, free water would be released in the middle region of the lower mantle, which suggests that no water can reach the deeper regions of the lower mantle. Here we use in situ X-ray measurements in conjunction with a multi-anvil apparatus using sintered diamond anvils to show that hydrous phases are stable under lower mantle conditions up to 50 GPa. We found that phase D transforms to an assemblage with another hydrous silicate (MgSiH2O4), named phase H, at pressures above about 48 GPa. Our results suggest that phase H is the dominant hydrous silicate in descending slabs, and may be found at depths far deeper than 1,250 km. We conclude that a significant amount of water is retained in the descending slabs and may be delivered to the deepest part of the lower mantle.
Print ISSN:
1752-0894
Digitale ISSN:
1752-0908
Thema:
Geologie und Paläontologie
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