Partial melting of stagnant oceanic lithosphere in the mantle transition zone and its geophysical implications

Zhang, Yanfei; Wang, Chao; Zhang, Jin; Zhu, Lüyun

doi:10.1016/j.lithos.2017.09.019

Cited by 11 publications

(15 citation statements)

References 68 publications

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“…It is unlikely that the basaltic oceanic crust (eclogite) and the sediments were the source of the buoyancy, because eclogite and continental crustal materials are denser than the ambient peridotite in the depth range of the deep upper mantle and MTZ 36,37 . In contrast, hydrous mantle peridotite is less dense than dry mantle peridotite, and the hydrous fluids and partial melts can also be less dense than the host hydrous peridotite in the MTZ 34 . Therefore, hydrated mantle peridotite beneath the basaltic oceanic crust in the subducted Pacific plate and/or peridotite in the MTZ above the slab are the sources of the compositional buoyancy that formed the hydrous mantle plume beneath Changbaishan (Fig.…”

Section: Discussionmentioning

confidence: 95%

“…However, the source of the buoyancy of the mantle plume, i.e. thermal 33 , compositional 11,18,34 , or both 7,35 , remains controversial, because the water contents of the source mantle have yet to be reliably estimated. We estimated the mantle potential temperature for the plume as 1310–1360 °C by OBS1 and 1330–1400 °C by the model of ref.…”

Section: Discussionmentioning

confidence: 99%

“…1b). The dehydration of the slab peridotite in the MTZ and/or CO 2 release from the carbonated basaltic slab could have occurred in the MTZ and played an important role in the rehydration or re-carbonation of the peridotite in the MTZ 9,34,35 . Electrical conductivity studies have suggested that the MTZ beneath Northeast China is hydrous 16 with as much as ~1 wt.% water 17 .…”

Section: Discussionmentioning

confidence: 99%

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Buoyant hydrous mantle plume from the mantle transition zone

Kuritani

Xia

Kimura

et al. 2019

Sci Rep

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Magmatism at some intraplate volcanoes and large igneous provinces (LIPs) in continental areas may originate from hydrous mantle upwelling (i.e. a plume) from the mantle transition zone (MTZ) at 410–660 km depths in the Earth’s deep interior. However, the ultimate origin of the magmatism, i.e. why mantle plumes could have been generated at the MTZ, remains unclear. Here, we study the buoyancy of a plume by investigating basalts from the Changbaishan volcano, beneath which a mantle plume from the hydrous MTZ is observed via seismology. Based on carefully determined water contents of the basalts, the potential temperature of the source mantle is estimated to be 1310–1400 °C, which is within the range of the normal upper mantle temperature. This observation suggests that the mantle plume did not have a significant excess heat, and that the plume upwelled because of buoyancy resulting from water supplied from the Pacific slab in the MTZ. Such a hydrous mantle plume can account for the formation of extremely hydrous LIP magmatism. The water was originally sourced from a stagnant slab and stored in the MTZ, and then upwelled irrespective of the presence or absence of a deep thermal plume.

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Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Buoyant hydrous mantle plume from the mantle transition zone

Kuritani

Xia

Kimura

et al. 2019

Sci Rep

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“…As water preferentially partitions into melts compared to solid peridotite residues (Aubaud et al, 2004;Novella et al, 2014), partial melts of hydrous material from the MTZ are expected to be water-rich (up to 16.5 wt% H 2 O), supported by observations from melting experiments (Freitas et al, 2017;Litasov & Ohtani, 2002;Zhang et al, 2017) and insight from thermodynamic modeling (Hirschmann et al, 2009;Novella et al, 2017). Whether these water-rich melts stay at depth-and therefore provide a viable explanation for the geophysical observations-is an open question, as they appear to be far too water-rich to be neutrally buoyant.…”

Section: Introductionmentioning

confidence: 81%

Structure and Density of H₂O‐Rich Mg₂SiO₄ Melts at High Pressure From Ab Initio Simulations

2020

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Water has a strong effect on silicate melt properties, yet its dissolution mechanism in depolymerized melts, typical for mantle composition, remains poorly understood. Here we report results of first-principles molecular dynamics simulations for hydrous Mg 2 SiO 4 melts with 6, 16, and 27 wt% H 2 O at pressure and temperature conditions relevant to the upper mantle and mantle transition zone. The results show that hydrogen bonds not only to the network-forming cation Si but also to Mg which-nevertheless-remains the most important network modifier. There is no evidence to support the hypothesis based on experimental data that water may cause an increase in melt polymerization for ultramafic magmas; the ratio of non-bridging oxygen per Si increases with the addition of the oxygen from H 2 O. The partial molar volume of water is independent on concentration in our simulations which allows us to examine the density of hydrous melt systematically. The critical water content-at which melts are neutrally buoyant compared to the surrounding mantle-is~4 wt% H 2 O for a pyrolite composition, much lower than the high water content (>10 wt%) observed in petrological experiments and estimated thermodynamically for low-degree partial melts formed in the vicinity of the mantle transition zone. Plain Language Summary Geophysical observations indicate abrupt changes in the material properties of the Earth's mantle right below and above the transition zone, at a depth between 410 and 660 km. The existence of low-velocity and high conductivity layers near this region is often taken as an indication for melting caused by the presence of water. However, the density of such hydrous melts is not well characterized over the relevant pressure-temperature range. Here we present new simulations on Mg 2 SiO 4 melts with a wide range of water concentrations to address this issue. The water content at which hydrous melts have the same density as the surrounding mantle is about 4 wt%, much lower than the high water content (>10 wt%) estimated for melts occurring in the Earth's mantle, suggesting they cannot experience long-term gravitational stability in the mantle transition zone and its vicinity. We further find that water does not cause a significant change in melt structure as proposed previously.

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“…The bulk composition of PC‐a falls well within the range of natural basalts, while the composition of PC‐b falls at the edge of exhumed rocks (Figure S1 and Text S1 in the supporting information). In harzburgite‐basalt reaction experiments, hydrous harzburgite was synthesized by mixing approximately 60 wt% olivine, 10 wt% enstatite, and 30 wt% antigorite, with an average H 2 O content of ~3.7 wt%, which is the same as we have used in a previous study (Zhang et al, 2017). Prior to each experiment, the starting material was kept in an oven and dried at 120°C for at least 24 hr before loading into the sample capsule, and then laser‐sealed to keep free of unwanted absorbed water and prevent the release of volatile components during the experiment.…”

Section: Methodsmentioning

confidence: 99%

Decarbonation of Stagnant Slab in the Mantle Transition Zone

2020

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Phase relations of carbonated basalts have been investigated at 13–20 GPa and 1200–1600°C, to model the decarbonation process of stagnant slab in the mantle transition zone (MTZ). Two synthetic mixes with CO2 contents of 2.5 wt% (PC‐a) and 5.0 wt% (PC‐b) were used as the starting materials. The estimated solidus was ~1350°C at the top of the MTZ (~13–15 GPa), which declined to ~1250°C for pressures of above ~15–16 GPa for both mixes. The average slab geotherms are lower than the obtained solidus, creating a carbonate‐bearing stagnant slab, followed by decarbonation of stagnant slab with increased residence time. Dehydration of stagnant oceanic lithosphere could induce decarbonation of the upper oceanic crust for temperatures below the solidus of carbonated basalts. The resulting carbonate melt is highly reactive with the ambient mantle, producing a carbonated domain in the MTZ or at the top of the 410‐km seismic discontinuity. A portion of carbonate melt could ascend to shallow depth because of low density and low viscosity and bring oceanic crust signatures into the source of some volcanoes after complex interactions with the surrounding mantle. On the example of Eastern Asia, decarbonation of stagnant slab is inferred to be a possible prerequisite for the formation of the big mantle wedge and triggered the intraplate volcanoes of Eastern Asia.

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Partial melting of stagnant oceanic lithosphere in the mantle transition zone and its geophysical implications

Cited by 11 publications

References 68 publications

Buoyant hydrous mantle plume from the mantle transition zone

Buoyant hydrous mantle plume from the mantle transition zone

Structure and Density of H₂O‐Rich Mg₂SiO₄ Melts at High Pressure From Ab Initio Simulations

Decarbonation of Stagnant Slab in the Mantle Transition Zone

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Partial melting of stagnant oceanic lithosphere in the mantle transition zone and its geophysical implications

Cited by 11 publications

References 68 publications

Buoyant hydrous mantle plume from the mantle transition zone

Buoyant hydrous mantle plume from the mantle transition zone

Structure and Density of H2O‐Rich Mg2SiO4 Melts at High Pressure From Ab Initio Simulations

Decarbonation of Stagnant Slab in the Mantle Transition Zone

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Structure and Density of H₂O‐Rich Mg₂SiO₄ Melts at High Pressure From Ab Initio Simulations