Hydrous melting and partitioning in and above the mantle transition zone: Insights from water-rich MgO–SiO2–H2O experiments

Myhill, Robert; Frost, Daniel J.; Novella, Davide

doi:10.1016/j.gca.2016.05.027

Cited by 17 publications

(17 citation statements)

References 54 publications

(64 reference statements)

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“…These results also show that the amount of water retained in slabs sinking deeper into the mantle could be highly variable. Such variability in water content could impact intermediate depth seismicity in the slab (Hacker et al, 2003b;Omori et al, 2004), release of water in the transition zone (Richard et al, 2007;Leahy and Bercovici, 2007;Myhill et al, 2017) and transport of water into the lower mantle (Hirschmann, 2006).…”

Section: Discussionmentioning

confidence: 99%

Decoupling of plate-asthenosphere motion caused by non-linear viscosity during slab folding in the transition zone

Billen

Arredondo

2018

Physics of the Earth and Planetary Interiors

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Although most present-day subduction zones are in trench retreat, plate reconstructions and geological observations show that individual margins experience episodes of advancing, retreating or stationary trench motion with timevariable subduction rates. However, most laboratory and numerical simulations predict steady plate velocities and sustained trench retreat unless the slab experiences folding in the transition zone. Using 2D dynamical models of subduction with a mobile trench and overriding plate, we find that rapid sinking of the slab during folding causes a reduction in asthenosphere viscosity through the non-linear rheology, which allows the overriding plate to move in the opposite direction of the asthenosphere. This decoupling of the direction of plate and asthenosphere flow allows for episodes of rapid trench advance after each slab folding event. By analyzing the interaction between slab deformation (sinking direction and speed), stress-induced changes in asthenosphere viscosity, asthenosphere flow and plate motions, we show that there are three modes of slab-flow-plate interaction: 1) coupled trench retreat during rapid vertical sinking, 2) coupled trench advance during prograde sinking of the slab, and 3) decoupled, rapid trench advance during folding with prograde motion of the shallow slab and retrograde motion of the deep slab. These results show that non-linear viscosity plays an important role in determining the force balance controlling trench motion and conversely that trench motion can be used as a constraint on the asthenosphere viscosity underlying the overriding plate. In addition, cooling by several hundreds of degrees during episodes of fast subduction could lead to a reduction in slab dehydration and fluid-induced melting in the mantle wedge. Such cold episodes would also likely lead to time-variability in the water content and related geochemical tracers in erupted lavas, as well as the amount of water being transported by slabs into the deep mantle.

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Section: Discussionmentioning

confidence: 99%

Decoupling of plate-asthenosphere motion caused by non-linear viscosity during slab folding in the transition zone

Billen

Arredondo

2018

Physics of the Earth and Planetary Interiors

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“…Silver and Stolper 1985;Medard and Grove, 2008;Hirschmann et al, 2009;Myhill et al, 2016 (Burnham 1975(Burnham , 1979(Burnham , 1994Stolper, 1982;Silver and Stolper, 1989;Zotov and Keppler, 1998), i.e.…”

Section: Model For Hydrous Melting Of Mg 2 Sio 4 and Mgsiomentioning

confidence: 99%

Melting phase relations in the systems Mg2SiO4–H2O and MgSiO3–H2O and the formation of hydrous melts in the upper mantle

Novella

Dolejš

Myhill

et al. 2017

Geochimica et Cosmochimica Acta

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms A temperature dependent equilibrium constant is necessary to reproduce the data, however, implying that molecular H 2 O becomes more important in the melt with decreasing temperature. The data for hydrous forsterite melting at 13 GPa are inconclusive due to uncertainties in the anhydrous melting temperature at these conditions. When applied to results on natural peridotite melt systems at similar conditions, the same model infers the presence mainly of molecular H 2 O, implying a significant difference in physiochemical behavior between simple and complex hydrous

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“…H 2 O, which is present as H + or OH − in minerals, plays an important role in geological processes in the Earth's interior, affecting the physical and chemical properties of its surroundings such as melting temperature, melt composition, and phase relations (e.g., Inoue 1994;Chang et al 2017;Hwang et al 2017;Myhill et al 2017). Water may be transported into the deep Earth via subducting slabs within hydrous phase.…”

Section: Introductionmentioning

confidence: 99%

Solubility behavior of δ-AlOOH and ε-FeOOH at high pressures

Nishi

Inoue

2019

American Mineralogist

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Low-pressure polymorphs of AlOOH and FeOOH are common natural oxyhydroxides at the Earth's surface, which may transport hydrogen to the deep mantle via subduction. At elevated pressures, the low-pressure polymorphs transform into δ-AlOOH and ε-FeOOH with CaCl2-type structure, which form a solid solution above 18 GPa. Nevertheless, few studies have examined the solid solution behavior of this binary system in detail. In this study, we ascertain the phase relations in the AlOOH–FeOOH binary system at 15–25 GPa and 700–1200 °C. X-ray diffraction (XRD) measurements of quenched samples show that δ-AlOOH and ε-FeOOH partly form solid solutions over wide pressure and temperature ranges. Our results demonstrate that a binary eutectic diagram is formed without dehydration or melting below 1200 °C at 20 GPa. We also observe that the maximum solubilities of Al and Fe in the solid solutions are more strongly influenced by temperature than pressure. Our results suggest that the CaCl2-type hydroxides subducted into the deep mantle form a solid solution over a wide composition range. As AlOOH and FeOOH are present in hydrous crust, these phases may be subducted into the deep interior, transporting a significant amount of hydrogen to deeper regions. Therefore, a better understanding of this binary system may help elucidate the model geodynamic processes associated with the deep water cycling in the Earth.

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Hydrous melting and partitioning in and above the mantle transition zone: Insights from water-rich MgO–SiO2–H2O experiments

Cited by 17 publications

References 54 publications

Decoupling of plate-asthenosphere motion caused by non-linear viscosity during slab folding in the transition zone

Decoupling of plate-asthenosphere motion caused by non-linear viscosity during slab folding in the transition zone

Melting phase relations in the systems Mg2SiO4–H2O and MgSiO3–H2O and the formation of hydrous melts in the upper mantle

Solubility behavior of δ-AlOOH and ε-FeOOH at high pressures

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