Experimental evidence supporting a global melt layer at the base of the Earth’s upper mantle

Freitas, D.; Manthilake, Geeth; Schiavi, Federica; Chantel, Julien; Bolfan-Casanova, Nathalie; Bouhifd, Mohamed Ali; Andrault, Denis

doi:10.1038/s41467-017-02275-9

Cited by 47 publications

(71 citation statements)

References 61 publications

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“…The water contents inferred here for the transition zone show large variability and are relatively modest (∼0.1 wt %) beneath geomagnetic observatories located in Europe, Africa, and Northern Australia but high (∼0.5-1 wt %) underneath stations in North America, Asia, and Southern Australia. These water contents are consistent with what has been experimentally determined (∼0.2 wt %) by Freitas et al (2017). Since there is no evidence from geodynamic models that the "410 km" discontinuity acts as a barrier to mantle flow (e.g Christensen, 2001), material that is advected into the bottom of the upper mantle with passive upwellings may provide an explanation for how subducted water is being continuously drained from the transition zone and reenters the upper mantle and becomes remixed there.…”

Section: 1002/2017jb014691supporting

confidence: 92%

“…In the water filter hypothesis by Bercovici and Karato (2003), this process is expected to occur globally rather than being restricted to localized water-rich upwellings. Experimental and seismic evidence in support of localized melt layers on top of the transition zone (around 410 km depth) has also accumulated in the form of observations of low shear wave velocity anomalies at various locations of which many appear to be associated with areas where subduction has recently or is currently taking place (Freitas et al, 2017). Experimental and seismic evidence in support of localized melt layers on top of the transition zone (around 410 km depth) has also accumulated in the form of observations of low shear wave velocity anomalies at various locations of which many appear to be associated with areas where subduction has recently or is currently taking place (Freitas et al, 2017).…”

Section: Transition Zone Temperature and Water Contentmentioning

confidence: 99%

“…Although an accurate characterization of the melt layer is beyond the scope of this work, our results nonetheless suggest that the water filter hypothesis is only likely to be operative on a local/regional scale. Experimental and seismic evidence in support of localized melt layers on top of the transition zone (around 410 km depth) has also accumulated in the form of observations of low shear wave velocity anomalies at various locations of which many appear to be associated with areas where subduction has recently or is currently taking place (Freitas et al, 2017). The locations include western, central, and eastern United States (Courtier & Revenaugh, 2006;Jasbinsek & Dueker, 2007;Song et al, 2004;Song & Helmberger, 2006), Siberian platform (Vinnik & Farra, 2007), Arabian Plate (Vinnik et al, 2003), off the coast of Japan (Bagley et al, 2009;Revenaugh & Sipkinf, 1994), Southwest Pacific (Courtier & Revenaugh, 2007), and Afar Triple Junction in East Africa (Thompson et al, 2015).…”

Section: 1002/2017jb014691mentioning

confidence: 99%

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Stochastic Inversion of Geomagnetic Observatory Data Including Rigorous Treatment of the Ocean Induction Effect With Implications for Transition Zone Water Content and Thermal Structure

et al. 2018

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In this paper we estimate and invert local electromagnetic (EM) sounding data for 1‐D conductivity profiles in the presence of nonuniform oceans and continents to most rigorously account for the ocean induction effect that is known to strongly influence coastal observatories. We consider a new set of high‐quality time series of geomagnetic observatory data, including hitherto unused data from island observatories installed over the last decade. The EM sounding data are inverted in the period range 3–85 days using stochastic optimization and model exploration techniques to provide estimates of model range and uncertainty. The inverted conductivity profiles are best constrained in the depth range 400–1,400 km and reveal significant lateral variations between 400 km and 1,000 km depth. To interpret the inverted conductivity anomalies in terms of water content and temperature, we combine laboratory‐measured electrical conductivity of mantle minerals with phase equilibrium computations. Based on this procedure, relatively low temperatures (1200–1350°C) are observed in the transition zone (TZ) underneath stations located in Southern Australia, Southern Europe, Northern Africa, and North America. In contrast, higher temperatures (1400–1500°C) are inferred beneath observatories on islands, Northeast Asia, and central Australia. TZ water content beneath European and African stations is ∼0.05–0.1 wt %, whereas higher water contents (∼0.5–1 wt %) are inferred underneath North America, Asia, and Southern Australia. Comparison of the inverted water contents with laboratory‐constrained water storage capacities suggests the presence of melt in or around the TZ underneath four geomagnetic observatories in North America and Northeast Asia.

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Section: 1002/2017jb014691supporting

confidence: 92%

Section: Transition Zone Temperature and Water Contentmentioning

confidence: 99%

Section: 1002/2017jb014691mentioning

confidence: 99%

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Stochastic Inversion of Geomagnetic Observatory Data Including Rigorous Treatment of the Ocean Induction Effect With Implications for Transition Zone Water Content and Thermal Structure

et al. 2018

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“…The mantle radial viscosity profile inferred from geoid anomalies, glacial isostasy adjustment data, and mineral physics predicts the existence of a weak asthenosphere (Figure 1d; Forte et al, 2010;Hager & Richards, 1989;Mitrovica & Forte, 2004;Peslier et al, 2010) whose viscosity ranges from 10 18 to 10 20 Pa•s. In particular, recent geophysical observations and mineral experiments demonstrate that a global melt layer due to enriched water contents may be located at depths of 350-410 km in the upwelling mantle, which may cause the decrease in viscosity in the asthenosphere (Freitas et al, 2017;Tauzin et al, 2010;Vinnik & Farra, 2007). In addition, another thin weak layer beneath the mantle transition zone is proposed in the mantle radial viscosity profile (Mitrovica & Forte, 2004) and has a large effect on subduction stagnation (Mao & Zhong, 2018), possibly caused by grain size reduction (Panasyuk & Hager, 1998) or the presence of water (Pearson et al, 2014;Tschauner et al, 2018).…”

Section: Methodsmentioning

confidence: 99%

Plume ‐Tree Structure Induced by Low‐Viscosity Layers in the Upper Mantle

Líu

Leng

2020

Geophysical Research Letters

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Previous seismological results and geodynamic modeling showed that mantle plumes have thin tails. However, the latest geophysical observations reveal the presence of broad and bifurcate plumes in the lower and upper mantle, providing a new challenge to further understand the evolution of plume morphology. Here, developing 3‐D numerical models, we demonstrate that a plume shaped like a tree, derived from the mantle transition zone, branches up to surface volcanoes due to the combined influence of weak layers in the asthenosphere and the mantle transition zone. Clusters of mantle plumes likely explain the simultaneous occurrence of multiple subparallel hot spot tracks in the Pacific and Atlantic Oceans. Meanwhile, the mantle plume wandering at a rate of ~1.5 cm/year in the upper mantle without a strong mantle wind provides a new mechanism for hot spot motions. Thus, our model represents a significant advance for linking plume studies in seismology, geochemistry, and plate reconstruction.

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“…The idea of a melt layer atop the MTZ is supported by electrical conductivity depth profiles computed from magnetotelluric and geomagnetic depth sounding in the southwestern United States (Toffelmier & Tyburczy, ). Recently, the wadsleyite‐to‐olivine transition has been experimentally reproduced (Freitas et al, ). Accordingly, a 0.7% melt fraction in peridotite is suitable to explain a v S anomaly of ~−4%.…”

Section: Discussionmentioning

confidence: 99%

A Sequence of up to 11 Seismic Discontinuities Down to the Midmantle Beneath Southeast Asia

Rümpker

2018

Geochem Geophys Geosyst

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The Earth's mantle exhibits a layered structure seismically characterized by sudden velocity changes or strong gradients. Several seismic boundaries have been identified in the mantle, and a large number of theoretical calculations and laboratory experiments have contributed to the debate on their origin. We analyze P‐to‐S converted phases generated at such interfaces to image the velocity structure within the sublithospheric mantle beneath Indonesia. Our study confirms the existence of various layer boundaries in the upper and lower mantle revealing up to 11 consecutive discontinuities down to ~1,700‐km depth. We detect Ps phases from the Lehmann and the X discontinuities originating at ~245 and ~294 km, respectively, followed by the top of a low‐velocity layer (LVL‐410) at ~368 km. The transition zone discontinuities are imaged at average depths of 408 and 665 km, respectively, which indicates the absence of significant temperature anomalies. In the midmantle we find vague indications for another interface at ~970‐km depth. At ~1,220 km a negative phase is observed followed by a sequence of converting structures of unknown origin at ~1,320, ~1,460, and ~1,500 km. We interpret these interfaces as compositional anomalies related to persisting fragments of subducted lithosphere. A further boundary is observed at ~1,700 km. Even though different causes exist to explain the observed seismic discontinuities including mineral phase transitions, partial melt, and chemical changes, most of them require additional mineral components. Thus, our findings provide clear evidence for significant compositional alteration of the mantle beneath Indonesia as a result of recurring subduction.

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Experimental evidence supporting a global melt layer at the base of the Earth’s upper mantle

Cited by 47 publications

References 61 publications

Stochastic Inversion of Geomagnetic Observatory Data Including Rigorous Treatment of the Ocean Induction Effect With Implications for Transition Zone Water Content and Thermal Structure

Stochastic Inversion of Geomagnetic Observatory Data Including Rigorous Treatment of the Ocean Induction Effect With Implications for Transition Zone Water Content and Thermal Structure

Plume ‐Tree Structure Induced by Low‐Viscosity Layers in the Upper Mantle

A Sequence of up to 11 Seismic Discontinuities Down to the Midmantle Beneath Southeast Asia

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