Phase transformation of hydrous ringwoodite to the lower-mantle phases and the formation of dense hydrous silica

Abstract To understand the effects of H2O on the mineral phases forming under the pressure-temperature conditions of the lower mantle, we have conducted laser-heated diamond-anvil cell experiments on hydrous ringwoodite (Mg2SiO4 with 1.1 wt% H2O) at pressures between 29 and 59 GPa and temperatures between 1200 and 2400 K. Our results show that hydrous ringwoodite (hRw) converts to crystalline dense hydrous silica, stishovite (Stv) or CaCl2-type SiO2 (mStv), containing 1 wt% H2O together with Brd and MgO at the pressure-temperature conditions expected for shallow lower-mantle depths between approximately 660 to 1600 km. Considering the lack of sign for melting in our experiments, our preferred interpretation of the observation is that Brd partially breaks down to dense hydrous silica and periclase (Pc), forming the phase assembly Brd + Pc + Stv. The results may provide an explanation for the enigmatic coexistence of Stv and Fp inclusions in lower-mantle diamonds.

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Dehydration of δ-AlOOH in Earth’s Deep Lower Mantle

Minerals ◽

10.3390/min10040384 ◽

2020 ◽

Vol 10 (4) ◽

pp. 384 ◽

Cited By ~ 2

Author(s):

Hélène Piet ◽

Kurt D. Leinenweber ◽

Jacqueline Tappan ◽

Eran Greenberg ◽

Vitali B. Prakapenka ◽

...

Keyword(s):

Iron Oxide ◽

Chemical Composition ◽

Metallic Iron ◽

Lower Mantle ◽

Diamond Anvil Cell ◽

Iron Hydroxide ◽

Temperature Conditions ◽

Iron Hydride ◽

Diamond Anvil ◽

Laser Heated

δ -AlOOH has been shown to be stable at the pressure–temperature conditions of the lower mantle. However, its stability remains uncertain at the conditions expected for the lowermost mantle where temperature is expected to rise quickly with increasing depth. Our laser-heated diamond-anvil cell experiments show that δ -AlOOH undergoes dehydration at ∼2000 K above 90 GPa. This dehydration temperature is lower than geotherm temperatures expected at the bottom ∼700 km of the mantle and suggests that δ -AlOOH in warm slabs would dehydrate in this region. Our experiments also show that the released H 2 O from dehydration of δ -AlOOH can react with metallic iron, forming iron oxide, iron hydroxide, and possibly iron hydride. Our observations suggest that H 2 O from the dehydration of subducting slabs, if it occurs, could alter the chemical composition of the surrounding mantle and core regions.

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Approach to the mineralogy of the lower mantle by a combined method of a laser-heated diamond anvil cell experiment and analytical electron microscopy

Physics of The Earth and Planetary Interiors ◽

10.1016/j.pepi.2003.11.013 ◽

2004 ◽

Vol 143-144 ◽

pp. 215-221 ◽

Cited By ~ 5

Author(s):

Kiyoshi Fujino ◽

Yohei Sasaki ◽

Toyohisa Komori ◽

Hisayuki Ogawa ◽

Nobuyoshi Miyajima ◽

...

Keyword(s):

Electron Microscopy ◽

Lower Mantle ◽

Diamond Anvil Cell ◽

Analytical Electron Microscopy ◽

Combined Method ◽

Cell Experiment ◽

Analytical Electron ◽

Diamond Anvil ◽

Laser Heated

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3D analytical investigation of melting at lower mantle conditions in the laser-heated diamond anvil cell

European Microscopy Congress 2016: Proceedings ◽

10.1002/9783527808465.emc2016.6178 ◽

2016 ◽

pp. 1180-1181

Author(s):

Farhang Nabiei ◽

Marco Cantoni ◽

James Badro ◽

Susannah Dorfman ◽

Richard Gaal ◽

...

Keyword(s):

Lower Mantle ◽

Diamond Anvil Cell ◽

Analytical Investigation ◽

Diamond Anvil ◽

Laser Heated

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Exploring microstructures in lower mantle mineral assemblages with synchrotron x-rays

Science Advances ◽

10.1126/sciadv.abd3614 ◽

2021 ◽

Vol 7 (1) ◽

pp. eabd3614

Author(s):

Brian Chandler ◽

Joel Bernier ◽

Mathew Diamond ◽

Martin Kunz ◽

Hans-Rudolf Wenk

Keyword(s):

Lower Mantle ◽

Diamond Anvil Cell ◽

Seismic Anisotropy ◽

X Rays ◽

Interconnected Network ◽

Individual Crystal ◽

Mantle Mineral ◽

Mineral Assemblages ◽

Diamond Anvil ◽

Laser Heated

Understanding dynamics across phase transformations and the spatial distribution of minerals in the lower mantle is crucial for a comprehensive model of the evolution of the Earth’s interior. Using the multigrain crystallography technique (MGC) with synchrotron x-rays at pressures of 30 GPa in a laser-heated diamond anvil cell to study the formation of bridgmanite [(Mg,Fe)SiO3] and ferropericlase [(Mg,Fe)O], we report an interconnected network of a smaller grained ferropericlase, a configuration that has been implicated in slab stagnation and plume deflection in the upper part of the lower mantle. Furthermore, we isolated individual crystal orientations with grain-scale resolution, provide estimates on stress evolutions on the grain scale, and report {110} twinning in an iron-depleted bridgmanite, a mechanism that appears to aid stress relaxation during grain growth and likely contributes to the lack of any appreciable seismic anisotropy in the upper portion of the lower mantle.

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