Growth of ringwoodite reaction rims from MgSiO3 perovskite and periclase at 22.5 GPa and 1,800 °C

Shimojuku, Akira; Boujibar, A.; Yoshino, Takashi; Tomioka, Naotaka; Xu, Junshan

doi:10.1007/s00269-014-0669-x

Cited by 7 publications

(9 citation statements)

References 43 publications

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“…Only one previous study has investigated the retrograde reaction across the 660 km discontinuity: Shimojuku et al (2014) reacted MgSiO 3 perovskite single crystals with MgO single crystals at 22.5 GPa and 1800 • C. Rim thicknesses and the derived reaction rate constant from Shimojuku et al (2014) are plotted in Figs. 2A and 3: they are comparable to, but somewhat slower than, those of the present study.…”

Section: Comparison With Previous Resultsmentioning

confidence: 99%

“…Farnetani and Hofmann, 2009) and which might be coarser than the surrounding mantle (e.g. Solomatov, 1996;Korenaga, 2005). The increased plume temperature of, perhaps 500 K hotter than the normal mantle, will act against these factors increasing reaction rates by one order of magnitude: this effect is small compared to the effect of the enhanced upwelling rate at plumes.…”

Section: Implications For the Mantle Above 660 Kmmentioning

confidence: 96%

“…Hydrostatic experiments that studied the growth kinetics of the perovskite-ferropericlase assemblage have shown that this is sluggish (Yamazaki et al, 1996), resulting in an inferred lower-mantle grain size of <100 μm. This conclusion has been questioned by subsequent studies: (1) Solomatov et al (2002) argue that the experiments were not sufficiently long to evaluate grain growth kinetics beyond the transient effects due to textural re-equilibration of lamellar intergrowths produced by the eutectoid post-spinel reaction; (2) experiments in which the analogue system Mg 2 SiO 4 olivine plus MgO was deformed in superplastic creep (Hiraga et al, 2010) suggest that deformation might enhance grain growth through a process of grain-boundary sliding and grain switching; (3) it has also been suggested, on the basis of (i) the temperature of the plume source region, (ii) the kinetics of grain growth from an early magma ocean and (iii) seismic tomographic imaging of wide plume roots, that deep-mantle plumes might have a significantly larger grain size than the ambient lower mantle (Solomatov, 1996;Korenaga, 2005).…”

Section: Introductionmentioning

confidence: 98%

“…This should result in a reaction rate which is strongly sensitive to the grain size of the lower mantle and, if the metastable ferropericlase + majoritic garnet assemblage has different seismic properties from the equilibrium ringwoodite + garnet assemblage, the position and form of the 660 km discontinuity might contain useful information regarding the grain size of the lower mantle. A recent study (Shimojuku et al, 2014) investigated the kinetics of the reaction of perovskite plus periclase to ringwoodite in the simple Mg-Si-O system and found the kinetics to be sufficiently fast that no discernable shallowing of the 660 km seismic discontinuity should occur at plumes due to the kinetics of reaction.…”

Section: Introductionmentioning

confidence: 98%

“…However, it is consistent with the other experiments suggesting that the kinetics of the growth of the ringwoodite layer is the same regardless of the aluminium content of the garnet. The triangle, labelled Y14, is from the data ofShimojuku et al (2014), for MgSiO 3 perovskite-MgO reaction at 22.5 GPa.…”

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confidence: 99%

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The kinetics of the reaction of majorite plus ferropericlase to ringwoodite: Implications for mantle upwellings crossing the 660 km discontinuity

Dobson¹,

Mariani²

2014

Earth and Planetary Science Letters

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We have measured the kinetics of reaction between MgO and majoritic garnet at 20 GPa and 1773-2123 K as a proxy for the reaction between perovskite and ferropericlase during mantle upwelling across the 660 km seismic discontinuity. Ringwoodite forms a layer between MgO and garnet and, in the case of aluminous garnets the interface between ringwoodite and garnet develops a fingering instability resulting in a complex intergrowth at this interface. By contrast, the MgO-ringwoodite interface is always planar for an initial planar MgO-garnet interface. Two thicknesses are therefore defined; (1) a layer thickness, X 1 , which is the maximum thickness of ringwoodite which forms a plane-parallel bounded layer next to the MgO, and (2) an interface thickness, X 2 , which is the maximum extent of the intergrowth region away from the ringwoodite layer. The growth of both of these regions can be described by apparent rate constants, k i , which are Arrhenius with ln(k 0 1 ) = −6.36 ± 0.25 m 2 /s and E 1 = 456 ± 40 kJ/mol for the ringwoodite layer, and ln(k 0 2 ) = −9.2 ± 3.3 m 2 /s and E 2 = 371 ± 53 kJ/mol for the intergrowth region. The fingering instability is caused by the incompatibility of aluminium in ringwoodite and its low chemical diffusivity in garnet which results in an increase of surface area at the ringwoodite-garnet interface to minimise the aluminium concentration at the interface. The intergrowth region contains a fine-grained mixture of ringwoodite and garnet which coarsens very slowly with time. This might result in a transient weakening of upwelling regions of mantle just above the 660 km seismic discontinuity allowing some viscous decoupling between the upper and lower mantle.

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Section: Comparison With Previous Resultsmentioning

confidence: 99%

Section: Implications For the Mantle Above 660 Kmmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 98%

mentioning

confidence: 99%

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The kinetics of the reaction of majorite plus ferropericlase to ringwoodite: Implications for mantle upwellings crossing the 660 km discontinuity

Dobson¹,

Mariani²

2014

Earth and Planetary Science Letters

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Textural and compositional complexities resulting from coupled dissolution–reprecipitation reactions in geomaterials

Altree-Williams

Pring

Ngothai

et al. 2015

Earth-Science Reviews

130

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Sharp 660-km discontinuity controlled by extremely narrow binary post-spinel transition

et al. 2019

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The Earth's mantle is characterised by a sharp seismic discontinuity at a depth of 660-km that can provide insights into deep mantle processes. The discontinuity occurs over only 2km -or a pressure difference of 0.1 GPa -and is thought to result from the post-spinel transition, that is, the decomposition of the mineral ringwoodite to bridgmanite plus ferropericlase. Existing high-pressure-temperature experiments have lacked the pressure control required to test whether such sharpness is the result of isochemical phase relations or chemically distinct upper and lower mantle domains. Here, we obtain the isothermal pressure interval of the Mg-Fe binary post-spinel transition by applying advanced multianvil techniques with in situ X-ray diffraction with help of Mg-Fe partition experiments. It is demonstrated that the interval at mantle compositions and temperatures is only 0.01 GPa, corresponding to 250 m. This interval is indistinguishable from zero at seismic frequencies. These results can explain the discontinuity sharpness and provide new support for whole mantle convection in a chemically homogeneous mantle. The present work suggests that distribution of adiabatic vertical flows between the upper and lower mantles can be mapped based on discontinuity sharpness. Main:The 660-km seismic discontinuity (D660) is the boundary between the upper and lower mantles. Seismological studies based on short-period P-wave reflections (Pʹ660Pʹ-PʹPʹ) have demonstrated that D660 is extremely sharp and less than 2 km thick 1 , which is in striking contrast to the 7-km-thick 410-km discontinuity 1 . Understanding the nature of D660 from a perspective of mineral physics provides important clues to open questions about the structure and dynamic processes in the Earth's mantle, such as slab subduction and upwelling of hot plume.Geochemical studies suggest that the Earth's upper mantle consists of ca. 60% atom-

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Growth of ringwoodite reaction rims from MgSiO3 perovskite and periclase at 22.5 GPa and 1,800 °C

Cited by 7 publications

References 43 publications

The kinetics of the reaction of majorite plus ferropericlase to ringwoodite: Implications for mantle upwellings crossing the 660 km discontinuity

The kinetics of the reaction of majorite plus ferropericlase to ringwoodite: Implications for mantle upwellings crossing the 660 km discontinuity

Textural and compositional complexities resulting from coupled dissolution–reprecipitation reactions in geomaterials

Sharp 660-km discontinuity controlled by extremely narrow binary post-spinel transition

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