Pervasive low-velocity layer atop the 410-km discontinuity beneath the northwest Pacific subduction zone: Implications for rheology and geodynamics

Han, Guilai; Li, Juan; Guo, Guanhua; Mooney, Walter D.; Karato, Shun‐ichiro; Yuen, David A.

doi:10.1016/j.epsl.2020.116642

Cited by 23 publications

(22 citation statements)

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“…It has been proposed that water can be transported to this depth by either metallic iron (Liu et al, 2018) or garnet (Panero et al, 2020) before release into the surrounding lower-mantle mineral assemblage. In the deep Japan subduction zone, an LVZ located above the MTZ has been detected using seismic tomography (Zhao & Ohtani, 2009), travel-time triplications (Han et al, 2021), and receiver functions (Liu et al, 2016;. Additionally, Liu et al (2016) imaged an LVZ at ∼750 km, directly below the Japan slab.…”

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confidence: 99%

Seismic Evidence of Mid‐Mantle Water Transport Beneath the Yellowstone Region

Frazer

Park

2021

Geophysical Research Letters

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The hydration potential of Earth's mantle transition zone (MTZ) may be responsible for long-term (∼100 Ma) ocean-mass regulation, driven by plate tectonics and mantle convection (Bercovici & Karato, 2003;Karato et al., 2020). Constraining the solid-Earth water cycle over geologic time is key in understanding the volatile-compound budget and planetary habitability (Langmuir & Broecker, 2012). Minerals within the MTZ, primarily wadsleyite and ringwoodite, are able to store 1-3 wt% of water (Kohlstedt et al., 1996), far greater than minerals in the upper or lower mantle. Typical upper-mantle rock is estimated to have a maximum water content of ∼0.1 wt% from mid-ocean ridge basalts and a water storage capacity of ∼0.1 wt% (Hirschmann, 2006;Saal et al., 2002). The lower-mantle is estimated to have similarly low water capacity (Bolfan-Casanova, 2005). High water capacity does not necessarily imply high water content, but some deep xenoliths provide evidence for a hydrous MTZ. Water-rich diamond inclusions have been found with water content of 1.4 wt% (Pearson et al., 2014) and ice VII inclusions (Tschauner et al., 2018). Electrical conductivity measurements have also supported high water content in the MTZ, with large regional variations (Karato, 2011). The combination of high-water storage capacity and geologic evidence suggest the MTZ is a key component of the solid-Earth water cycle.When water-rich material from the transition zone penetrates the upper or lower mantle, partial melting occurs due to the decrease in water capacity after phase transition, generating a seismic low-velocity zone (LVZ). In order for melt to generate low-velocity anomalies, grain-boundaries must wet significantly (Yoshino et al., 2007). Such LVZs have been detected above and below the MTZ, and have been interpreted as

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confidence: 99%

Seismic Evidence of Mid‐Mantle Water Transport Beneath the Yellowstone Region

Frazer

Park

2021

Geophysical Research Letters

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“…The 410‐km discontinuity (the 410), as the upper boundary of the Earth's mantle transition zone (MTZ), is thought to reflect the pressure‐induced transformation from olivine to wadsleyite and, in general, is treated as a water‐filter barrier (Cammarano & Romanowicz, 2007; Ringwood, 1976; Wu et al., 2019). A low‐velocity layer above the 410 was explained as partial melt and may exist worldwide (Han et al., 2021; Song et al., 2004; Tauzin et al., 2010). On the other hand, mineral physical research revealed a high water storage capacity of the nominally anhydrous minerals wadsleyite and ringwoodite in the MTZ conditions (Demouchy et al., 2005; Ohtani et al., 2004).…”

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confidence: 99%

Velocity Gradients Below the 410‐km Discontinuity Beneath Eastern Asia and Its Implication on Water Content Distribution

2022

Geophysical Research Letters

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The velocity gradient below the 410‐km discontinuity provides clues for the water content gradient in the mantle transition zone. Here we report an abnormal X phase refracted below the 410, providing a unique opportunity to constrain the velocity gradient at that depth. We observe the X phase sampling the MTZ beneath south and southwest China close to the subducted Paleo‐Pacific slab, compared to the typical triplication waveforms sampling northeast Asia, the modern Pacific subduction system. The P velocity gradient below the 410 is 0.0028 s−1 or lower beneath south and southwest China, indicating a uniform water content; while it is 0.0037 s−1 or higher beneath northeast Asia, suggesting a water content decreasing from the 410‐km downward. Our research provides seismic evidence for water infiltrating the MTZ from a hydrous layer atop the 410 and then widely diffused into the MTZ after long‐term subduction.

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“…Since the first discovery by Revenaugh and Sipkin (1994) from multiple‐ScS reverberation mapping in northeast Asia, a seismic low velocity layer (LVL) above the mantle transition zone (MTZ) has been observed with a thickness ranging from

\sim

20 to 90 km in a number of tectonic settings, including convergent oceanic margins, plume, and continental collision zones (Tauzin et al., 2010; Vinnik & Farra, 2007; Wei & Shearer, 2017). Seismological methods used to detect such a LVL range from multiple‐ScS reverberations (Bagley et al., 2009; Courtier & Revenaugh, 2007; Revenaugh & Sipkin, 1994), receiver functions (Liu et al., 2016; Tauzin et al., 2010, 2017; Vinnik & Farra, 2002, 2007), SS precursors (Wei & Shearer, 2017), body wave triplications (Gao et al., 2006; Han et al., 2021; Song et al., 2004), and seismic tomography (Obayashi et al., 2006). Marked by a sharp interface with the overlying mantle and a 2%–6% reduction in shear wave velocity, the LVL is generally recognized as a chemical, rather than thermal, anomaly.…”

Section: Introductionmentioning

confidence: 99%

“…A number of recent rock physics analyses suggest that the LVL is characterized by an average of 0.5-1 vol% partial melt embedded in a silicate matrix (Freitas et al, 2017;Hier-Majumder & Courtier, 2011;Hier-Majumder & Tauzin, 2017;Hier-Majumder et al, 2014;Xiao et al, 2020). While it is plausible that the LVL is a global phenomenon (Tauzin et al, 2010), the highest resolution of its internal structure is obtained from regional studies, such as in the western US (Eagar et al, 2010;Fee & Dueker, 2004;Hier-Majumder & Tauzin, 2017;Jasbinsek & Dueker, 2007;Jasbinsek et al, 2010;Schmandt & Humphreys, 2011;Song et al, 2004;Tauzin et al, 2013) and northeast Asia (Bagley et al, 2009;Han et al, 2021;Revenaugh & Sipkin, 1994;Liu et al, 2016). Especially useful in this respect are seismic results obtained from receiver function studies that, in addition to the reduction in shear wave velocities, provide information regarding the thickness of the MTZ (Chevrot et al, 1999;Lawrence & Shearer, 2006;Tauzin et al, 2008).…”

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confidence: 99%

“…As a small amount of these volatiles can apparently lower the solidus and viscosity of mantle rocks, they are intuitively implied to play an important role in the upper mantle dynamics. Our study focuses on the northeast Asian low-velocity layer (LVL), a layer of 61 E wave triplications (Gao et al, 2006;Han et al, 2021;Song et al, 2004), and seismic tomography (Obayashi et al, 2006). Marked by a sharp interface with the overlying mantle and a 2%-6% reduction in shear wave velocity, the LVL is generally recognized as a chemical, rather than thermal, anomaly.…”

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confidence: 99%

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