A nearly water-saturated mantle transition zone inferred from mineral viscosity

Fei, Hongzhan; Yamazaki, Daisuke; Sakurai, Masahiro; Miyajima, Nobuyoshi; Ohfuji, Hiroaki; Katsura, Tomoo; Yamamoto, Takafumi

doi:10.1126/sciadv.1603024

Cited by 89 publications

(79 citation statements)

References 44 publications

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“…Although a number of studies have suggested a water‐rich MTZ, from investigations of observed ringwoodite diamond inclusions (Pearson et al, ) to regional seismological analyses of reflected phases (e.g., Schmandt et al, ), electrical conductivity models (e.g., Karato, ), and laboratory measurements of mineral viscosity (Fei et al, ), our study suggests a regional variability in possible water content even beneath subduction zones that is more complex than previously thought.…”

Section: The Origin Of Radial Anisotropy In the Mtz: Water Content Immentioning

confidence: 44%

Inference on Water Content in the Mantle Transition Zone Near Subducted Slabs From Anisotropy Tomography

Chang

Ferreira

2019

Geochem Geophys Geosyst

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We examine the patterns of radial anisotropy in global tomography images of the mantle transition zone near subducted slabs in the western Pacific. Fast SV velocity anomalies are observed in this region, which are compatible with anisotropy due to lattice-preferred orientation in wadsleyite. Using mineral physics reports of the dependency of the strength of radial anisotropy on water content in wadsleyite, we estimate the water content in the transition zone near subducted slabs from the tomography images. We find that fast SV anisotropy anomalies over~1.5% observed beneath subduction zones in the western Pacific are compatible with a low water content (smaller than~3,000 ppm H/SI), notably beneath the Tonga-Kermadec trenches, the Philippines, and the Sumatra trench.Plain Language Summary Tectonic plates plunge into the mantle at trenches, carrying water from the oceans. Some of this water may go down to the mantle transition zone between 410-and 660-km depth, where minerals have a large water storage capacity. In this study, we use observations of seismic anisotropy, the directional dependency of seismic wave speed, which is sensitive to the water content in the mantle transition zone. We find that the mantle transition zone beneath some subduction zones is drier than previously thought.

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Section: The Origin Of Radial Anisotropy In the Mtz: Water Content Immentioning

confidence: 44%

Inference on Water Content in the Mantle Transition Zone Near Subducted Slabs From Anisotropy Tomography

Chang

Ferreira

2019

Geochem Geophys Geosyst

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“…Regional-scale seismic studies suggest variable water content of the MTZ (Courtier & Revenaugh, 2006;Emry et al, 2015;Liu et al, 2016;Van der Lee et al, 2008;Van der Meijde et al, 2003); however, recent viscosity measurements of hydrated ringwoodite suggest a globally saturated transition zone (Fei et al, 2017). Evaluating the regional-scale water content of the MTZ is important to understanding Earth's deep water cycle (Hirschmann, 2006;Jacobsen & Van der Lee, 2006;Karato, 2011;Ohtani et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

HyMaTZ: A Python Program for Modeling Seismic Velocities in Hydrous Regions of the Mantle Transition Zone

Wang

Barklage

Lou

et al. 2018

Geochem Geophys Geosyst

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Mapping the spatial distribution of water in the mantle transition zone (MTZ, 410‐ to 660‐km depth) may be approached by combining thermodynamic and experimental mineral physics data with regional studies of seismic velocity and seismic discontinuity structure. HyMaTZ (Hydrous Mantle Transition Zone) is a Python program with graphical user interface, which calculates and displays seismic velocities for different scenarios of hydration in the MTZ for comparison to global or regional seismic‐velocity models. The influence of water is applied through a regression to experimental data on how H2O influences the thermoelastic properties of (Mg,Fe)2SiO4 polymorphs: olivine, wadsleyite, and ringwoodite. Adiabatic temperature profiles are internally consistent with dry phase proportion models; however, modeling hydration in HyMaTZ affects only velocities and not phase proportions or discontinuity structure. For wadsleyite, adding 1.65 wt% H2O or increasing the iron content by 7 mol% leads to roughly equivalent reductions in VS as raising the temperature by 160 K with a pyrolite model in the upper part of the MTZ. The eastern U.S. low‐velocity anomaly, which has been interpreted as the result of dehydration of the Farallon slab in the top of the lower mantle, is consistent with hydration of wadsleyite to about 20% of its water storage capacity in the upper MTZ. Velocity gradients with depth in absolute shear velocity models are steeper in all seismic models than all mineralogical models, suggesting that the seismic velocity gradients should be lowered or varied with depth and/or an alternative compositional model is required.

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“…Based on an observation of a low SH velocity layer and high V p / V s , Li et al () suggested a hydrated MTZ in this region according to the experiment by Jacobsen and Smyth (), who pointed out the velocity discordance between the compressional and shear wave on hydrous ringwoodite. The presence of water in the MTZ has also been revealed by petrological and other geophysical studies and predicted by mineral physics experiments (e.g., Fei et al, ; Houser, ; Mao et al, ; Pearson et al, ; Wang et al, ). If we attribute the ~2.7% increase of V p / V s ratio to the water effect alone, then the water content would be ~1.2–1.8 wt% in the MTZ beneath Northeast Asia based on the experimental data on iron‐bearing wet ringwoodite (Jacobsen et al, ; Jacobsen & Smyth, ; Thio et al, ).…”

Section: Discussionmentioning

confidence: 73%

“…Some researchers suggested that the MTZ beneath Northeast Asia is hydrous (0.2-0.4 wt %; Li et al, 2013;Ye et al, 2011) due to intensive hydration by ancient slab subduction and stagnation (Kuritani et al, 2011) through water transport into deep mantle (Ohtani et al, 2004;Song et al, 2007). More recently, Fei et al (2017) argued that the MTZ should be nearly water-saturated (1-2 wt %) globally based on mantle viscosity fitting result. On the other hand, some researches believed that little water exists in the MTZ (e.g., Houser, 2016;Yoshino et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Mantle Transition Zone Structure Beneath Northeast Asia From 2‐D Triplicated Waveform Modeling: Implication for a Segmented Stagnant Slab

et al. 2019

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The structure of the mantle transition zone (MTZ) in subduction zones is essential for understanding subduction dynamics in the deep mantle and its surface responses. We constructed the P (Vp) and SH velocity (Vs) structure images of the MTZ beneath Northeast Asia based on two‐dimensional (2‐D) triplicated waveform modeling. In the upper MTZ, a normal Vp but 2.5% low Vs layer compared with IASP91 are required by the triplication data. In the lower MTZ, our results show a relatively higher‐velocity layer (+2% Vp and −0.5% Vs compared to IASP91) with a thickness of ~140 km and length of ~1,200 km atop the 660‐km discontinuity. Taking this anomaly as the stagnant slab and considering the plate convergence rate of 7–10 cm/year in the western Pacific region during the late Cenozoic, we deduced that the stagnant slab has a subduction age of less than 30 Ma. This suggests that the observed stagnancy of the slab in the MTZ beneath Northeast Asia may have occurred no earlier than the Early Oligocene. From the constraints derived individually on Vp and Vs structures, high Vp/Vs ratios are obtained for the entire MTZ beneath Northeast Asia, which may imply a water‐rich and/or carbonated environment. Within the overall higher‐velocity stagnant slab, a low‐velocity anomaly was further detected, with a width of ~150 km, Vp and Vs reductions of 1% and 3% relative to IASP91. Such a gap may have provided a passage for hot deep mantle materials to penetrate through the thick slab and feed the Changbaishan volcano.

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A nearly water-saturated mantle transition zone inferred from mineral viscosity

Abstract: The mantle transition zone contains 1 to 2 weight % water based on the viscosity difference between ringwoodite and bridgmanite.

Cited by 89 publications

References 44 publications

Inference on Water Content in the Mantle Transition Zone Near Subducted Slabs From Anisotropy Tomography

Inference on Water Content in the Mantle Transition Zone Near Subducted Slabs From Anisotropy Tomography

HyMaTZ: A Python Program for Modeling Seismic Velocities in Hydrous Regions of the Mantle Transition Zone

Mantle Transition Zone Structure Beneath Northeast Asia From 2‐D Triplicated Waveform Modeling: Implication for a Segmented Stagnant Slab

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